Publications by year
Gatis N, Anderson K, Grand-Clement E, Luscombe D, Hartley I, Smith D, Brazier R (In Press). Evaluating MODIS vegetation products using digital images for quantifying local peatland CO2 gas fluxes. Remote Sensing in Ecology and Conservation
Lugli LF, Andersen KM, Aragao LEOC, Cordeiro AL, Cunha HFV, Fuchslueger L, Meir P, Mercado LM, Oblitas E, Quesada CA, et al (In Press). Multiple phosphorus acquisition strategies adopted by fine roots in low-fertility soils in Central Amazonia. Plant and Soil
Gatis N, Luscombe D, Grand-Clement E, Hartley I, Anderson K, Smith DM, Brazier RE (In Press). The effect of drainage ditches on vegetation diversity and CO2 fluxes in a Molinia caerulea dominated peatland. Ecohydrology
Cox AJF, Hartley IP, Meir P, Sitch S, Dusenge ME, Restrepo Z, González-Caro S, Villegas JC, Uddling J, Mercado LM, et al
(2023). Acclimation of photosynthetic capacity and foliar respiration in Andean tree species to temperature change. New Phytol
Acclimation of photosynthetic capacity and foliar respiration in Andean tree species to temperature change.
Climate warming is causing compositional changes in Andean tropical montane forests (TMFs). These shifts are hypothesised to result from differential responses to warming of cold- and warm-affiliated species, with the former experiencing mortality and the latter migrating upslope. The thermal acclimation potential of Andean TMFs remains unknown. Along a 2000 m Andean altitudinal gradient, we planted individuals of cold- and warm-affiliated species (under common soil and irrigation), exposing them to the hot and cold extremes of their thermal niches, respectively. We measured the response of net photosynthesis (Anet ), photosynthetic capacity and leaf dark respiration (Rdark ) to warming/cooling, 5 months after planting. In all species, Anet and photosynthetic capacity at 25°C were highest when growing at growth temperatures (Tg ) closest to their thermal means, declining with warming and cooling in cold-affiliated and warm-affiliated species, respectively. When expressed at Tg , photosynthetic capacity and Rdark remained unchanged in cold-affiliated species, but the latter decreased in warm-affiliated counterparts. Rdark at 25°C increased with temperature in all species, but remained unchanged when expressed at Tg. Both species groups acclimated to temperature, but only warm-affiliated species decreased Rdark to photosynthetic capacity ratio at Tg as temperature increased. This could confer them a competitive advantage under future warming. Abstract
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He Y, Zhou X, Jia Z, Zhou L, Chen H, Liu R, Du Z, Zhou G, Shao J, Ding J, et al
(2023). Apparent thermal acclimation of soil heterotrophic respiration mainly mediated by substrate availability. Glob Chang Biol
Apparent thermal acclimation of soil heterotrophic respiration mainly mediated by substrate availability.
Multiple lines of existing evidence suggest that increasing CO2 emission from soils in response to rising temperature could accelerate global warming. However, in experimental studies, the initial positive response of soil heterotrophic respiration (RH ) to warming often weakens over time (referred to apparent thermal acclimation). If the decreased RH is driven by thermal adaptation of soil microbial community, the potential for soil carbon (C) losses would be reduced substantially. In the meanwhile, the response could equally be caused by substrate depletion, and would then reflect the gradual loss of soil C. To address uncertainties regarding the causes of apparent thermal acclimation, we carried out sterilization and inoculation experiments using the soil samples from an alpine meadow with 6 years of warming and nitrogen (N) addition. We demonstrate that substrate depletion, rather than microbial adaptation, determined the response of RH to long-term warming. Furthermore, N addition appeared to alleviate the apparent acclimation of RH to warming. Our study provides strong empirical support for substrate availability being the cause of the apparent acclimation of soil microbial respiration to temperature. Thus, these mechanistic insights could facilitate efforts of biogeochemical modeling to accurately project soil C stocks in the future climate. Abstract
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Xia S, Song Z, Singh BP, Guo L, Bolan N, Wang W, Lin G, Fang Y, Wen X, Wang J, et al
(2023). Contrasting patterns and controls of soil carbon and nitrogen isotope compositions in coastal wetlands of China. Plant and Soil
Contrasting patterns and controls of soil carbon and nitrogen isotope compositions in coastal wetlands of China
Aims: Natural stable isotope compositions of carbon (δ13C) and nitrogen (δ15N) can reveal biogeochemical mechanisms that control ecosystem carbon (C) and nitrogen (N) processes. However, little is known about the latitudinal patterns and controlling mechanisms for soil δ13C and δ15N in coastal wetlands based on a large spatial scale. Methods: a total of 76 sites of coastal wetlands were sampled along a 5000 km transect across temperate-subtropical-tropical zones to explore biological and environmental controls on soil stable C and N isotopic compositions. Results: the results showed that soil δ13C (ranging from -27.5‰ to -18.3‰) and δ15N (from 2.66‰ to 9.97‰) varied over a broad geographic scale. The C4-plant (Spartina alterniflora) dominated sites have 2–6‰ higher δ13C values than those of other vegetation types, while mangrove soils have lower δ13C values compared to those of marshes; and soils with vegetated C4-plants and mangroves have 1–3‰ higher δ15N values relative to native grass marshes. There were no significant relationships between mean annual temperature (MAT) or precipitation (MAP) and δ13C, but positive correlations between MAT and δ15N, as well as MAP and δ15N. Conclusions: Vegetation composition and plant C inputs directly control the spatial variability of δ13C patterns. Simultaneously, climate and edaphic variables (e.g. soil water content, pH, and C availability) are the predominant factors influencing δ15N patterns. These findings provide new insights into soil organic matter turnover and response to climate and environmental changes and improve the prediction of C stability and burial in coastal wetlands. Abstract
Sun S, Song Z, Chen B, Wang Y, Ran X, Fang Y, Van Zwieten L, Hartley IP, Wang Y, Li Q, et al
(2023). Current and future potential soil organic carbon stocks of vegetated coastal ecosystems and their controls in the Bohai Rim Region, China. Catena
Current and future potential soil organic carbon stocks of vegetated coastal ecosystems and their controls in the Bohai Rim Region, China
Vegetated coastal ecosystems (VCEs) have much higher organic carbon sequestration rates and storage capacities than most other earth surface ecosystems, and thus play a vital role in blue carbon sequestration for climate change mitigation. However, soil organic carbon (SOC) stock assessment in VCEs at a large regional-scale remain problematic, and the controlling mechanisms for SOC remain poorly understood. Here, we estimated current and future SOC stocks of VCEs in the Bohai Rim Region, China at a spatial resolution of 10 m, using a data-driven method based on multi-source data; and investigated the key environmental and anthropogenic controls. The total SOC stocks and SOC density of VCEs in the Bohai Rim Region were estimated to be approximately 62.7 Tg carbon and about 68.8 Mg ha−1, respectively (in the upper 1 m of soil). We found that climate and soil salinity are the most critical environmental controls of SOC stocks within VCEs in the region. Increasing temperature and soil salinity would increase SOC decomposition and decrease plant productivity, resulting in a decrease in SOC stocks. Conversely, increasing precipitation would increase SOC stocks by reducing soil salinity. We projected that the potential losses of SOC stocks due to the combined effects of climate changes, sea-level rise, and anthropogenic disturbances would be ∼ 12.2 % between 2041 and 2060 under two Shared Socioeconomic Pathway (SSP) scenarios (SSP245 and SSP585), extending to 19.3 % between 2081 and 2100. The decreases in SOC stocks would occur mainly in the higher latitude and colder regions. The study demonstrated the potential significant reduction in SOC stocks in coastal ecosystems and provided an important framework for better understanding the blue carbon ecosystems. Abstract
Xia S, Song Z, Wang W, Fan Y, Guo L, Van Zwieten L, Hartley IP, Fang Y, Wang Y, Zhang Z, et al (2023). Patterns and determinants of plant‐derived lignin phenols in coastal wetlands: Implications for organic C accumulation. Functional Ecology, 37(4), 1067-1081.
Michel J, Hartley IP, Buckeridge KM, van Meegen C, Broyd RC, Reinelt L, Ccahuana Quispe AJ, Whitaker J
(2023). Preferential substrate use decreases priming effects in contrasting treeline soils. Biogeochemistry
Preferential substrate use decreases priming effects in contrasting treeline soils
Climate change currently manifests in upward and northward shifting treelines, which encompasses changes to the carbon (C) and nitrogen (N) composition of organic inputs to soils. Whether these changed inputs will increase or decrease microbial mineralisation of native soil organic matter remains unknown, making it difficult to estimate how treeline shifts will affect the C balance. Aiming to improve mechanistic understanding of C cycling in regions experiencing treeline shifts, we quantified priming effects in soils of high altitudes (Peruvian Andes) and high latitudes (subarctic Sweden), differentiating landcover types (boreal forest, tropical forest, tundra heath, Puna grassland) and soil horizons (organic, mineral). In a controlled laboratory incubation, soils were amended with substrates of different C:N, composed of an organic C source at a constant ratio of 30% substrate-C to microbial biomass C, combined with different levels of a nutrient solution neutral in pH. Substrate additions elicited both positive and negative priming effects in both ecosystems, independent from substrate C:N. Positive priming prevailed above the treeline in high altitudes and in mineral soils in high latitudes, where consequently climate change-induced treeline shifts and deeper rooting plants may enhance SOM-mineralisation and soil C emissions. However, such C loss may be compensated by negative priming, which dominated in the other soil types and was of larger magnitude than positive priming. In line with other studies, these results indicate a consistent mechanism linking decreased SOM-mineralisation (negative priming) to increased microbial substrate utilisation, suggesting preferential substrate use as a potential tool to support soil C storage. Graphical abstract: [Figure not available: see fulltext.]. Abstract
Yang X, Song Z, Guo L, Wang J, Ni Y, Li Z, Hao Q, Li Q, Wu L, Kuang W, et al (2023). Specific PhytOC fractions in rice straw and consequent implications for potential of phytolith carbon sequestration in global paddy fields. Science of the Total Environment, 856, 159229-159229.
Yang Y, Zhang X, Hartley IP, Dungait JAJ, Wen X, Li D, Guo Z, Quine TA
(2022). Contrasting rhizosphere soil nutrient economy of plants associated with arbuscular mycorrhizal and ectomycorrhizal fungi in karst forests (Apr, 10.1007/s11104-021-04950-9, 2021). PLANT AND SOIL
(1-2), 95-96. Author URL
Cunha HFV, Andersen KM, Lugli LF, Santana FD, Aleixo IF, Moraes AM, Garcia S, Di Ponzio R, Mendoza EO, Brum B, et al
(2022). Direct evidence for phosphorus limitation on Amazon forest productivity. Nature
Direct evidence for phosphorus limitation on Amazon forest productivity.
The productivity of rainforests growing on highly weathered tropical soils is expected to be limited by phosphorus availability1. Yet, controlled fertilization experiments have been unable to demonstrate a dominant role for phosphorus in controlling tropical forest net primary productivity. Recent syntheses have demonstrated that responses to nitrogen addition are as large as to phosphorus2, and adaptations to low phosphorus availability appear to enable net primary productivity to be maintained across major soil phosphorus gradients3. Thus, the extent to which phosphorus availability limits tropical forest productivity is highly uncertain. The majority of the Amazonia, however, is characterized by soils that are more depleted in phosphorus than those in which most tropical fertilization experiments have taken place2. Thus, we established a phosphorus, nitrogen and base cation addition experiment in an old growth Amazon rainforest, with a low soil phosphorus content that is representative of approximately 60% of the Amazon basin. Here we show that net primary productivity increased exclusively with phosphorus addition. After 2 years, strong responses were observed in fine root (+29%) and canopy productivity (+19%), but not stem growth. The direct evidence of phosphorus limitation of net primary productivity suggests that phosphorus availability may restrict Amazon forest responses to CO2 fertilization4, with major implications for future carbon sequestration and forest resilience to climate change. Abstract
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Li T, Zhang J, Wang X, Hartley IP, Zhang J, Zhang Y (2022). Fungal necromass contributes more to soil organic carbon and more sensitive to land use intensity than bacterial necromass. Applied Soil Ecology, 176, 104492-104492.
Zhou W, Wen S, Zhang Y, Gregory AS, Xu M, Shah SAA, Zhang W, Wu H, Hartley IP (2022). Long-term fertilization enhances soil carbon stability by increasing the ratio of passive carbon: evidence from four typical croplands. Plant and Soil, 478(1-2), 579-595.
Michel J, Hartley IP, Buckeridge KM, Meegen CV, Broyd R, Reinelt L, Quispe AJC, Whitaker J (2022). Preferential substrate use decreases priming effects in contrasting treeline soils.
Nakhavali MA, Mercado LM, Hartley IP, Sitch S, Cunha FV, di Ponzio R, Lugli LF, Quesada CA, Andersen KM, Chadburn SE, et al
(2022). Representation of the phosphorus cycle in the Joint UK Land Environment Simulator (vn5.5_JULES-CNP). Geoscientific Model Development
Representation of the phosphorus cycle in the Joint UK Land Environment Simulator (vn5.5_JULES-CNP)
Abstract. Most land surface models (LSMs), i.e. the land components of Earth system models Abstract
(ESMs), include representation of nitrogen (N) limitation on ecosystem
productivity. However, only a few of these models have incorporated phosphorus
(P) cycling. In tropical ecosystems, this is likely to be important as N
tends to be abundant, whereas the availability of rock-derived elements, such as
P, can be very low. Thus, without a representation of P cycling, tropical
forest response in areas such as Amazonia to rising atmospheric CO2
conditions remain highly uncertain. In this study, we introduced P dynamics
and its interactions with the N and carbon (C) cycles into the Joint UK Land
Environment Simulator (JULES). The new model (JULES-CNP) includes the
representation of P stocks in vegetation and soil pools, as well as key
processes controlling fluxes between these pools. We develop and evaluate
JULES-CNP using in situ data collected at a low-fertility site in the
central Amazon, with a soil P content representative of 60 % of soils
across the Amazon basin, to parameterize, calibrate, and evaluate JULES-CNP.
Novel soil and plant P pool observations are used for parameterization and
calibration, and the model is evaluated against C fluxes and stocks and
those soil P pools not used for parameterization or calibration. We then
evaluate the model at additional P-limited test sites across the Amazon and in
Panama and Hawaii, showing a significant improvement over the C- and CN-only
versions of the model. The model is then applied under elevated
CO2 (600 ppm) at our study site in the central Amazon to quantify the impact
of P limitation on CO2 fertilization. We compare our results against the
current state-of-the-art CNP models using the same methodology that was used
in the AmazonFACE model intercomparison study. The model is able to
reproduce the observed plant and soil P pools and fluxes used for evaluation
under ambient CO2. We estimate P to limit net primary productivity
(NPP) by 24 % under current CO2 and by 46 % under elevated
CO2. Under elevated CO2, biomass in simulations accounting for CNP
increase by 10 % relative to contemporary CO2 conditions, although it
is 5 % lower compared to CN- and C-only simulations. Our results
highlight the potential for high P limitation and therefore lower CO2 fertilization capacity in the Amazon rainforest with low-fertility soils.
Parker TC, Chomel M, Clemmensen KE, Friggens NL, Hartley IP, Johnson D, Kater I, Krab EJ, Lindahl BD, Street LE, et al (2022). Resistance of subarctic soil fungal and invertebrate communities to disruption of below‐ground carbon supply. Journal of Ecology, 110(12), 2883-2897.
(2022). Respiratory thermal response of wood decay basidiomycetes.
Respiratory thermal response of wood decay basidiomycetes
Terrestrial ecosystems absorb over one-quarter of anthropogenic carbon dioxide (CO2) released into the atmosphere each year. Heterotrophic soil microbial respiration, associated with the decomposition of organic matter, contributes to approximately half of the CO2 released from the terrestrial biosphere to the atmosphere per year. However, with increasing global temperatures, there is the potential for soil microbial respiration to increase, resulting in a substantial release of CO2 into the atmosphere, therefore contributing extensively to the positive land C-climate feedback and accelerating climate change. In the short-term (days-years), heterotrophic soil microbial respiration is strongly and positively related to temperature. In the long-term (years-decades), however, the positive response of soil microbial respiration to warming declines, which could be caused by direct (acclimation, evolution and species sorting) or indirect (e.g. substrate availability, moisture) effects of warming. The primary focus on whole soil microbial community responses has made it difficult to identify potential mechanisms involved in controlling long-term warming responses, thus the response of respiration to warming in the long term remains controversial. To address this uncertainty, it is necessary to study individual species and gradually more diverse and complex decomposer communities. To this end, the respiratory thermal response of wood decay basidiomycetes, the dominant decomposers of wood, were investigated. Respiration rates of individual species and two- and three-species assemblages of basidiomycetes and semi-natural wood decay communities, decomposing beech wood (Fagus sylvatica), were measured during a 90-day cooling approach. In addition, a warming approach was applied to the two- and three-species assemblages and semi-natural wood decay communities. The direction of any thermal response (decreased temperature sensitivity of respiration (compensatory), increased temperature sensitivity of respiration (enhancing), and no change in the temperature sensitivity of respiration (no response)) was determined. To increase our understanding of the respiratory thermal responses, the growth response of the basidiomycete species to temperature was also measured. Abstract
Following cooling, individual species of basidiomycetes showed an overall enhancing response, with no compensatory responses identified. Two-species assemblages and the three-species assemblage showed no thermal responses overall to cooling, but with some evidence of compensatory and enhancing responses. Semi-natural wood decomposing communities showed no thermal response overall to cooling, with more enhancing than compensatory responses detected. With warming, two-species assemblages showed no thermal response overall, with more compensatory than enhancing responses detected, whereas the three-species assemblage that was dominated by one species towards the end of incubation demonstrated a compensatory response overall. The compensatory responses from the two- and three-species assemblages were likely caused by exceeding the optimum temperature for growth for some species or by the differences in the progression of the species interactions. Therefore, there was little evidence of compensatory responses that would decrease the temperature sensitivity of respiration. Semi-natural wood decay communities showed no thermal response overall to warming, but some enhancing responses were identified.
The findings showed that the temperature sensitivity of wood decomposition was increased when basidiomycetes were grown alone, however, this was reduced during competitive interspecific interactions between basidiomycetes and species in wood decomposing communities. With increasing global temperatures, individual species, growing alone during the early colonisation and decomposition of wood and in decay columns in stable wood communities, may increase their respiration, but simple communities of interacting basidiomycetes and more diverse wood decomposing communities in natural systems, will more often cause no change in the temperature sensitivity of respiration overall. However, the species present in communities will most likely determine the direction and strength of respiratory responses to temperature, and thus the overall temperature sensitivity of respiration of wood decay communities. With limited evidence for compensatory responses and more evidence of enhancing responses detected, it is, thus, considered unlikely that the temperature sensitivity of wood decomposition will decline as global temperatures rise. Therefore, there remains the potential for a positive feedback to climate change through increased wood decomposition with warming.
Mariappan S, Hartley IP, Cressey EL, Dungait JAJ, Quine TA
(2022). Soil burial reduces decomposition and offsets erosion-induced soil carbon losses in the Indian Himalaya. Glob Chang Biol
Soil burial reduces decomposition and offsets erosion-induced soil carbon losses in the Indian Himalaya.
The extent to which soil erosion is a net source or sink of carbon globally remains unresolved but has the potential to play a key role in determining the magnitude of CO2 emissions from land-use change in rapidly eroding landscapes. The effects of soil erosion on carbon storage in low-input agricultural systems, in acknowledged global soil erosion hotspots in developing countries, are especially poorly understood. Working in one such hotspot, the Indian Himalaya, we measured and modelled field-scale soil budgets, to quantify erosion-induced changes in soil carbon storage. In addition, we used long-term (1-year) incubations of separate and mixed soil horizons to better understand the mechanisms controlling erosion-induced changes in soil carbon cycling. We demonstrate that high rates of soil erosion did not promote a net carbon loss to the atmosphere at the field scale. Furthermore, our experiments showed that rates of decomposition in the organic matter-rich subsoil layers in depositional areas were lower per unit of soil carbon than from other landscape positions; however, these rates could be increased by mixing with topsoils. The results indicate that, the burial of soil carbon, and separation from fresh carbon inputs, led to reduced rates of decomposition offsetting potential carbon losses during soil erosion and transport within the cultivated fields. We conclude that the high rates of erosion experienced in these Himalayan soils do not, in isolation, drive substantial emissions of organic carbon, and there is the potential to promote carbon storage through sustainable agricultural practice. Abstract
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Xia S, Song Z, Van Zwieten L, Guo L, Yu C, Wang W, Li Q, Hartley IP, Yang Y, Liu H, et al (2022). Storage, patterns and influencing factors for soil organic carbon in coastal wetlands of China. Global Change Biology, 28(20), 6065-6085.
Friggens NL, Hartley IP, Parker TC, Subke J, Wookey PA (2022). Trees out‐forage understorey shrubs for nitrogen patches in a subarctic mountain birch forest. Oikos, 2023(4).
Qiu S, Peng J, Quine TA, Green SM, Liu H, Liu Y, Hartley IP, Meersmans J (2022). Unraveling Trade‐Offs Among Reforestation, Urbanization, and Food Security in the South China Karst Region: How can a Hinterland Province Achieve SDGs?. Earth's Future, 10(12).
Friggens NL, Hartley IP, Grant HK, Parker TC, Subke J-A, Wookey PA
(2022). Whole-crown 13C-pulse labelling in a sub-arctic woodland to target canopy-specific carbon fluxes. Trees
Whole-crown 13C-pulse labelling in a sub-arctic woodland to target canopy-specific carbon fluxes
. Key message
. Whole-crown 13C-pulse labelling can target tree canopy C fluxes in regions with dense understorey cover and investigate how increased photosynthetic C inputs may affect whole-ecosystem C fluxes.
. Climate change-driven increases in plant productivity have been observed at high northern latitudes. These trends are driven, in part, by the increasing abundance of tall shrub and tree species in arctic ecosystems, and the advance of treelines. Higher plant productivity may alter carbon (C) allocation and, hence, ecosystem C cycling and soil C sequestration. It is important to understand the contributions that the newly established canopy forming overstorey species makes to C cycling in these ecosystems. However, the presence of a dense understorey cover makes this challenging, with established partitioning approaches causing disturbance and potentially introducing measurement artefacts. Here, we develop an in situ whole-crown 13C-pulse labelling technique to isolate canopy C fluxes in areas of dense understorey cover. The crowns of five mountain birch (Betula pubescens ssp. czerepanovii) trees were provided with a 13CO2 pulse using portable field equipment, and leaf samples were collected from neighbouring con-specific trees and hetero-specific understorey shrubs on days 1–10 and 377 post-crown labelling. We found effective and long-term enrichment of foliage in labelled trees, but no evidence of the 13C-signal in con- or hetero-specific neighbouring trees or woody shrubs. This method is promising and provides a valuable tool to isolate the role of canopy tree species in ecosystems with dense understorey cover.
Liang B, Liu H, Quine TA, Chen X, Hallett PD, Cressey EL, Zhu X, Cao J, Yang S, Wu L, et al
(2021). Analysing and simulating spatial patterns of crop yield in Guizhou Province based on artificial neural networks. Progress in Physical Geography
Analysing and simulating spatial patterns of crop yield in Guizhou Province based on artificial neural networks
The area of karst terrain in China covers 3.63×106 km2, with more than 40% in the southwestern region over the Guizhou Plateau. Karst comprises exposed carbonate bedrock over approximately 1.30×106 km2 of this area, which suffers from soil degradation and poor crop yield. This paper aims to gain a better understanding of the environmental controls on crop yield in order to enable more sustainable use of natural resources for food production and development. More precisely, four kinds of artificial neural network were used to analyse and simulate the spatial patterns of crop yield for seven crop species grown in Guizhou Province, exploring the relationships with meteorological, soil, irrigation and fertilization factors. The results of spatial classification showed that most regions of high-level crop yield per area and total crop yield are located in the central-north area of Guizhou. Moreover, the three artificial neural networks used to simulate the spatial patterns of crop yield all demonstrated a good correlation coefficient between simulated and true yield. However, the Back Propagation network had the best performance based on both accuracy and runtime. Among the 13 influencing factors investigated, temperature (16.4%), radiation (15.3%), soil moisture (13.5%), fertilization of N (13.5%) and P (12.4%) had the largest contribution to crop yield spatial distribution. These results suggest that neural networks have potential application in identifying environmental controls on crop yield and in modelling spatial patterns of crop yield, which could enable local stakeholders to realize sustainable development and crop production goals. Abstract
García-Palacios P, Crowther TW, Dacal M, Hartley IP, Reinsch S, Rinnan R, Rousk J, van den Hoogen J, Ye JS, Bradford MA, et al
(2021). Author Correction: Evidence for large microbial-mediated losses of soil carbon under anthropogenic warming (Nature Reviews Earth & Environment, (2021), 2, 7, (507-517), 10.1038/s43017-021-00178-4). Nature Reviews Earth and Environment
Author Correction: Evidence for large microbial-mediated losses of soil carbon under anthropogenic warming (Nature Reviews Earth & Environment, (2021), 2, 7, (507-517), 10.1038/s43017-021-00178-4)
In the original published article, the graphs in Figure 2 were incorrectly based on soil carbon density per soil mass, not soil carbon stocks per area as the axis labels indicated. Figure 2 and the legend have been updated to now reflect the use of soil carbon stock per unit area data. These changes do not affect the findings of the Perspective. These errors have been corrected in the HTML and PDF versions of the manuscript. Abstract
Yang Y, Zhang X, Hartley IP, Dungait JAJ, Wen X, Li D, Guo Z, Quine TA (2021). Contrasting rhizosphere soil nutrient economy of plants associated with arbuscular mycorrhizal and ectomycorrhizal fungi in karst forests. Plant and Soil, 470(1-2), 81-93.
García-Palacios P, Crowther TW, Dacal M, Hartley IP, Reinsch S, Rinnan R, Rousk J, van den Hoogen J, Ye J-S, Bradford MA, et al (2021). Evidence for large microbial-mediated losses of soil carbon under anthropogenic warming. Nature Reviews Earth & Environment, 2(7), 507-517.
Martins NP, Fuchslueger L, Fleischer K, Andersen KM, Assis RL, Baccaro FB, Camargo PB, Cordeiro AL, Grandis A, Hartley IP, et al
(2021). Fine roots stimulate nutrient release during early stages of leaf litter decomposition in a Central Amazon rainforest. Plant and Soil
Fine roots stimulate nutrient release during early stages of leaf litter decomposition in a Central Amazon rainforest
. Large parts of the Amazon rainforest grow on weathered soils depleted in phosphorus and rock-derived cations. We tested the hypothesis that in this ecosystem, fine roots stimulate decomposition and nutrient release from leaf litter biochemically by releasing enzymes, and by exuding labile carbon stimulating microbial decomposers.
. We monitored leaf litter decomposition in a Central Amazon tropical rainforest, where fine roots were either present or excluded, over 188 days and added labile carbon substrates (glucose and citric acid) in a fully factorial design. We tracked litter mass loss, remaining carbon, nitrogen, phosphorus and cation concentrations, extracellular enzyme activity and microbial carbon and nutrient concentrations.
. Fine root presence did not affect litter mass loss but significantly increased the loss of phosphorus and cations from leaf litter. In the presence of fine roots, acid phosphatase activity was 43.2% higher, while neither microbial stoichiometry, nor extracellular enzyme activities targeting carbon- and nitrogen-containing compounds changed. Glucose additions increased phosphorus loss from litter when fine roots were present, and enhanced phosphatase activity in root exclusions. Citric acid additions reduced litter mass loss, microbial biomass nitrogen and phosphorus, regardless of fine root presence or exclusion.
. We conclude that plant roots release significant amounts of acid phosphatases into the litter layer and mobilize phosphorus without affecting litter mass loss. Our results further indicate that added labile carbon inputs (i.e. glucose) can stimulate acid phosphatase production by microbial decomposers, highlighting the potential importance of plant-microbial feedbacks in tropical forest ecosystems.
Schaap KJ, Fuchslueger L, Hoosbeek MR, Hofhansl F, Martins NP, Valverde-Barrantes OJ, Hartley IP, Lugli LF, Quesada CA
(2021). Litter inputs and phosphatase activity affect the temporal variability of organic phosphorus in a tropical forest soil in the Central Amazon. PLANT AND SOIL
(1-2), 423-441. Author URL
Schaap KJ, Fuchslueger L, Hoosbeek MR, Hofhansl F, Martins NP, Valverde-Barrantes OJ, Hartley IP, Lugli LF, Quesada CA (2021). Litter inputs and phosphatase activity control the temporal variability of organic phosphorus in a tropical forest soil in the Central Amazon.
Zhou W, Wen S, Zhang Y, Gregory AS, Xu M, Shah SAA, Zhang W, Wu H, Hartley IP (2021). Long-term Fertilization Enhances Soil Carbon Stability by Increase the Ratio of Passive Carbon: Evidence from Four Typical Croplands.
Tian J, Zong N, Hartley IP, He N, Zhang J, Powlson D, Zhou J, Kuzyakov Y, Zhang F, Yu G, et al
(2021). Microbial metabolic response to winter warming stabilizes soil carbon. Glob Chang Biol
Microbial metabolic response to winter warming stabilizes soil carbon.
Current consensus on global climate change predicts warming trends with more pronounced temperature changes in winter than summer in the Northern Hemisphere at high latitudes. Moderate increases in soil temperature are generally related to faster rates of soil organic carbon (SOC) decomposition in Northern ecosystems, but there is evidence that SOC stocks have remained remarkably stable or even increased on the Tibetan Plateau under these conditions. This intriguing observation points to altered soil microbial mediation of carbon-cycling feedbacks in this region that might be related to seasonal warming. This study investigated the unexplained SOC stabilization observed on the Tibetan Plateau by quantifying microbial responses to experimental seasonal warming in a typical alpine meadow. Ecosystem respiration was reduced by 17%-38% under winter warming compared with year-round warming or no warming and coincided with decreased abundances of fungi and functional genes that control labile and stable organic carbon decomposition. Compared with year-round warming, winter warming slowed macroaggregate turnover rates by 1.6 times, increased fine intra-aggregate particulate organic matter content by 75%, and increased carbon stabilized in microaggregates within stable macroaggregates by 56%. Larger bacterial "necromass" (amino sugars) concentrations in soil under winter warming coincided with a 12% increase in carboxyl-C. These results indicate the enhanced physical preservation of SOC under winter warming and emphasize the role of soil microorganisms in aggregate life cycles. In summary, the divergent responses of SOC persistence in soils exposed to winter warming compared to year-round warming are explained by the slowing of microbial decomposition but increasing physical protection of microbially derived organic compounds. Consequently, the soil microbial response to winter warming on the Tibetan Plateau may cause negative feedbacks to global climate change and should be considered in Earth system models. Abstract
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Taylor CR, Janes-Bassett V, Phoenix GK, Keane B, Hartley IP, Davies JAC
(2021). Organic phosphorus cycling may control grassland responses to nitrogen deposition: a long-term field manipulation and modelling study. Biogeosciences
Organic phosphorus cycling may control grassland responses to nitrogen deposition: a long-term field manipulation and modelling study
Ecosystems limited in phosphorous (P) are widespread, yet there is limited understanding of how these ecosystems may respond to anthropogenic deposition of nitrogen (N) and the interconnected effects on the biogeochemical cycling of carbon (C), N, and P. Here, we investigate the consequences of enhanced N addition for the C-N-P pools of two P-limited grasslands, one acidic and one limestone, occurring on contrasting soils, and we explore their responses to a long-term nutrient-manipulation experiment. We do this by combining data with an integrated C-N-P cycling model (N14CP). We explore the role of P-access mechanisms by allowing these to vary in the modelling framework and comparing model plant-soil C-N-P outputs to empirical data. Combinations of organic P access and inorganic P availability most closely representing empirical data were used to simulate the grasslands and quantify their temporal response to nutrient manipulation. The model suggested that access to organic P is a key determinant of grassland nutrient limitation and responses to experimental N and P manipulation. A high rate of organic P access allowed the acidic grassland to overcome N-induced P limitation, increasing biomass C input to soil and promoting soil organic carbon (SOC) sequestration in response to N addition. Conversely, poor accessibility of organic P for the limestone grassland meant N provision exacerbated P limitation and reduced biomass input to the soil, reducing soil carbon storage. Plant acquisition of organic P may therefore play an important role in reducing P limitation and determining responses to anthropogenic changes in nutrient availability. We conclude that grasslands differing in their access to organic P may respond to N deposition in contrasting ways, and where access is limited, soil organic carbon stocks could decline. Abstract
Lugli LF, Rosa JS, Andersen KM, Di Ponzio R, Almeida RV, Pires M, Cordeiro AL, Cunha HFV, Martins NP, Assis RL, et al
(2021). Rapid responses of root traits and productivity to phosphorus and cation additions in a tropical lowland forest in Amazonia. New Phytol
Rapid responses of root traits and productivity to phosphorus and cation additions in a tropical lowland forest in Amazonia.
Soil nutrient availability can strongly affect root traits. In tropical forests, phosphorus (P) is often considered the main limiting nutrient for plants. However, support for the P paradigm is limited, and N and cations might also control tropical forests functioning. We used a large-scale experiment to determine how the factorial addition of nitrogen (N), P and cations affected root productivity and traits related to nutrient acquisition strategies (morphological traits, phosphatase activity, arbuscular mycorrhizal colonisation and nutrient contents) in a primary rainforest growing on low-fertility soils in Central Amazonia after 1 yr of fertilisation. Multiple root traits and productivity were affected. Phosphorus additions increased annual root productivity and root diameter, but decreased root phosphatase activity. Cation additions increased root productivity at certain times of year, also increasing root diameter and mycorrhizal colonisation. P and cation additions increased their element concentrations in root tissues. No responses were detected with N addition. Here we showed that rock-derived nutrients determined root functioning in low-fertility Amazonian soils, demonstrating not only the hypothesised importance of P, but also highlighting the role of cations. The changes in fine root traits and productivity indicated that even slow-growing tropical rainforests can respond rapidly to changes in resource availability. Abstract
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Nakhavali MA, Mercado L, Hartley IP, Sitch S, Cunha FV, Ponzio RD, Lugli LF, Quesada CA, Andersen KM, Chadburn SE, et al
(2021). Representation of phosphorus cycle in Joint UK Land Environment Simulator (vn5.5_JULES-CNP). Geoscientific Model Development Discussions
Representation of phosphorus cycle in Joint UK Land Environment Simulator (vn5.5_JULES-CNP)
Most Land Surface Models (LSMs), the land components of Earth system models (ESMs), include representation of N limitation on ecosystem productivity. However only few of these models have incorporated phosphorus (P) cycling. In tropical ecosystems, this is likely to be particularly important as N tends to be abundant but the availability of rock-derived elements, such as P, can be very low. Thus, without a representation of P cycling, tropical forest response in areas such as Amazonia to rising atmospheric CO2 conditions remains highly uncertain. In this study, we introduced P dynamics and its interactions with the N and carbon (C) cycles into the Joint UK Land Environment Simulator (JULES). The new model (JULES-CNP) includes the representation of P stocks in vegetation and soil pools, as well as key processes controlling fluxes between these pools. We evaluate JULES-CNP at the Amazon nutrient fertilization experiment (AFEX), a low fertility site, representative of about 60 % of Amazon soils. We apply the model under ambient CO2 and elevated CO2. The model is able to reproduce the observed plant and soil P pools and fluxes under ambient CO2. We estimate P to limit net primary productivity (NPP) by 24 % under current CO2 and by 46 % under elevated CO2. Under elevated CO2, biomass in simulations accounting for CNP increase by 10 % relative to at contemporary CO2, although it is 5 % lower compared with CN and C-only simulations. Our results highlight the potential for high P limitation and therefore lower CO2 fertilization capacity in the Amazon forest with low fertility soils. Abstract
Parker TC, Thurston AM, Raundrup K, Subke J-A, Wookey PA, Hartley IP
(2021). Shrub expansion in the Arctic may induce large-scale carbon losses due to changes in plant-soil interactions. PLANT AND SOIL
(1-2), 643-651. Author URL
Xia S, Wang W, Song Z, Kuzyakov Y, Guo L, Van Zwieten L, Li Q, Hartley IP, Yang Y, Wang Y, et al
(2021). Spartina alterniflora invasion controls organic carbon stocks in coastal marsh and mangrove soils across tropics and subtropics. Glob Chang Biol
Spartina alterniflora invasion controls organic carbon stocks in coastal marsh and mangrove soils across tropics and subtropics.
Coastal wetlands are among the most productive ecosystems and store large amounts of organic carbon (C)-the so termed "blue carbon." However, wetlands in the tropics and subtropics have been invaded by smooth cordgrass (Spartina alterniflora) affecting storage of blue C. To understand how S. alterniflora affects soil organic carbon (SOC) stocks, sources, stability, and their spatial distribution, we sampled soils along a 2500 km coastal transect encompassing tropical to subtropical climate zones. This included 216 samplings within three coastal wetland types: a marsh (Phragmites australis) and two mangroves (Kandelia candel and Avicennia marina). Using δ13 C, C:nitrogen (N) ratios, and lignin biomarker composition, we traced changes in the sources, stability, and storage of SOC in response to S. alterniflora invasion. The contribution of S. alterniflora-derived C up to 40 cm accounts for 5.6%, 23%, and 12% in the P. australis, K. candel, and A. marina communities, respectively, with a corresponding change in SOC storage of +3.5, -14, and -3.9 t C ha-1. SOC storage did not follow the trend in aboveground biomass from the native to invasive species, or with vegetation types and invasion duration (7-15 years). SOC storage decreased with increasing mean annual precipitation (1000-1900 mm) and temperature (15.3-23.4℃). Edaphic variables in P. australis marshes remained stable after S. alterniflora invasion, and hence, their effects on SOC content were absent. In mangrove wetlands, however, electrical conductivity, total N and phosphorus, pH, and active silicon were the main factors controlling SOC stocks. Mangrove wetlands were most strongly impacted by S. alterniflora invasion and efforts are needed to focus on restoring native vegetation. By understanding the mechanisms and consequences of invasion by S. alterniflora, changes in blue C sequestration can be predicted to optimize storage can be developed. Abstract
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Hartley IP, Hill TC, Chadburn SE, Hugelius G
(2021). Temperature effects on carbon storage are controlled by soil stabilisation capacities. Nature Communications
Temperature effects on carbon storage are controlled by soil stabilisation capacities
Physical and chemical stabilisation mechanisms are now known to play a critical role in controlling carbon (C) storage in mineral soils, leading to suggestions that climate warming-induced C losses may be lower than previously predicted. By analysing > 9,000 soil profiles, here we show that, overall, C storage declines strongly with mean annual temperature. However, the reduction in C storage with temperature was more than three times greater in coarse-textured soils, with limited capacities for stabilising organic matter, than in fine-textured soils with greater stabilisation capacities. This pattern was observed independently in cool and warm regions, and after accounting for potentially confounding factors (plant productivity, precipitation, aridity, cation exchange capacity, and pH). The results could not, however, be represented by an established Earth system model (ESM). We conclude that warming will promote substantial soil C losses, but ESMs may not be predicting these losses accurately or which stocks are most vulnerable. Abstract
Estop‐Aragonés C, Olefeldt D, Abbott BW, Chanton JP, Czimczik CI, Dean JF, Egan JE, Gandois L, Garnett MH, Hartley IP, et al (2020). Assessing the Potential for Mobilization of Old Soil Carbon After Permafrost Thaw: a Synthesis of. <sup>14</sup>. C Measurements from the Northern Permafrost Region. Global Biogeochemical Cycles, 34(9).
Williams M, Zhang Y, Estop-Aragonés C, Fisher JP, Xenakis G, Charman DJ, Hartley IP, Murton JB, Phoenix GK (2020). Boreal permafrost thaw amplified by fire disturbance and precipitation increases. Environmental Research Letters, 15(11), 114050-114050.
Taylor CR, Janes-Bassett V, Phoenix G, Keane B, Hartley IP, Davies JAC (2020). Carbon storage in phosphorus limited grasslands may decline in response to elevated nitrogen deposition: a long-term field manipulation and modelling study. , 2020, 1-37.
Gatis N, Luscombe DJ, Benaud P, Ashe J, Grand-Clement E, Anderson K, Hartley IP, Brazier RE (2020). Drain blocking has limited short-term effects on greenhouse gas fluxes in a Molinia caerulea dominated shallow peatland. Ecological Engineering, 158, 106079-106079.
Zhang Y, Xu C, Wang J, Yang T, Ke Y, Wu H, Zuo X, Luo W, Smith M, Borer E, et al (2020). Extreme drought alters the vertical distribution but not the total amount of grassland root biomass.
Cordeiro AL, Norby RJ, Andersen KM, Valverde‐Barrantes O, Fuchslueger L, Oblitas E, Hartley IP, Iversen CM, Gonçalves NB, Takeshi B, et al (2020). Fine‐root dynamics vary with soil depth and precipitation in a low‐nutrient tropical forest in the Central Amazonia. Plant-Environment Interactions, 1(1), 3-16.
Gatis N, Luscombe D, Benaud P, Ashe J, Grand-Clement E, Anderson K, Hartley I, Brazier R (2020). Gatis et al (2020) DATASET for Drain blocking has limited short-term effects on greenhouse gas fluxes in a Molinia caerulea dominated shallow peatland Ecological Engineering.
Wang Y, Dungait JAJ, Xing K, Green SM, Hartley I, Tu C, Quine TA, Tian J, Kuzyakov Y
(2020). Persistence of soil microbial function at the rock-soil interface in degraded karst topsoils. LAND DEGRADATION & DEVELOPMENT
(2), 251-265. Author URL
(2020). Quantifying the temperature independent controls of nocturnal plant respiration.
Quantifying the temperature independent controls of nocturnal plant respiration
Autotrophic respiration is a critical determinant of plant, ecosystem and global carbon exchange, constituting a major control on the evolution of the contemporary carbon cycle with the potential to modulate the magnitude of future climate change. Due to an incomplete understanding of plant respiration and its underlying mechanisms, the process remains an important yet poorly quantified component of the global carbon cycle and currently dominates uncertainties in carbon cycle modelling. Plant respiration is currently represented by a fixed exponential temperature function in vegetation and earth system models. This rather simplistic description is inadequate to describe the co-regulation of respiration by endogenous mechanisms over longer timescales, such as the control exerted by substrate supply, product demand and the circadian clock. This study compiles the first comprehensive dataset of nocturnal leaf respiration to explore and quantify the temperature-independent control of leaf respiratory metabolism at night. A down-regulation in nocturnal respiration was observed to occur under constant temperature conditions which decreased the basal rate of respiration by ~40% of the initial rate at the onset of darkness, indicating the base rate of respiration cannot be considered constant as generally assumed in all modern field studies and models. An empirically derived term representing the non-temperature dependent component of leaf respiration at night was applied to the land surface component of an earth system model to describe nocturnal variation in endogenous metabolism in addition to the temperature dependency of respiration. Accounting for the non-temperature dependency of nocturnal respiration reduced annual rates of modelled plant respiration by up to 10% and increased annual net primary productivity by up to 16% across all tropical and temperate forest sites, suggesting that previous models have overestimated global respiration and underestimated net primary productivity, particularly in the tropics. The significant impact of the novel term presents important implications for land-atmosphere studies and estimates of global terrestrial carbon balance and storage. This study provides the foundation from which to advance research on endogenous rhythms in plant metabolism to develop a more comprehensive understanding and description of plant respiration for modelling frameworks, ultimately to increase the realism of vegetation models for greater confidence in simulations of the current and future terrestrial and global carbon cycle. Abstract
Van Langenhove L, Janssens IA, Verryckt L, Brechet L, Hartley IP, Stahl C, Courtois E, Urbina I, Grau O, Sardans J, et al (2020). Rapid root assimilation of added phosphorus in a lowland tropical rainforest of French Guiana. Soil Biology and Biochemistry, 140, 107646-107646.
Parker TC, Clemmensen KE, Friggens NL, Hartley IP, Johnson D, Lindahl BD, Olofsson J, Siewert MB, Street LE, Subke J-A, et al
(2020). Rhizosphere allocation by canopy-forming species dominates soil CO2 efflux in a subarctic landscape. New Phytol
Rhizosphere allocation by canopy-forming species dominates soil CO2 efflux in a subarctic landscape.
In arctic ecosystems, climate change has increased plant productivity. As arctic carbon (C) stocks predominantly are located belowground, the effects of greater plant productivity on soil C storage will significantly determine the net sink/source potential of these ecosystems, but vegetation controls on soil CO2 efflux remain poorly resolved. In order to identify the role of canopy-forming species in belowground C dynamics, we conducted a girdling experiment with plots distributed across 1 km2 of treeline birch (Betula pubescens) forest and willow (Salix lapponum) patches in northern Sweden and quantified the contribution of canopy vegetation to soil CO2 fluxes and belowground productivity. Girdling birches reduced total soil CO2 efflux in the peak growing season by 53%, which is double the expected amount, given that trees contribute only half of the total leaf area in the forest. Root and mycorrhizal mycelial production also decreased substantially. At peak season, willow shrubs contributed 38% to soil CO2 efflux in their patches. Our findings indicate that C, recently fixed by trees and tall shrubs, makes a substantial contribution to soil respiration. It is critically important that these processes are taken into consideration in the context of a greening arctic because productivity and ecosystem C sequestration are not synonymous. Abstract
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Xia S, Song Z, Van Zwieten L, Guo L, Yu C, Hartley IP, Wang H
(2020). Silicon accumulation controls carbon cycle in wetlands through modifying nutrients stoichiometry and lignin synthesis of Phragmites australis. Environmental and Experimental Botany
Silicon accumulation controls carbon cycle in wetlands through modifying nutrients stoichiometry and lignin synthesis of Phragmites australis
Silicon (Si) is one of the most abundant elements in the Earth's crust but its role in governing the biogeochemical cycling of other elements remains poor understood. There is a paucity of information on the role of Si in wetland plants, and how this may alter wetland C production and storage. Therefore, this study investigated Si distribution, nutrient stoichiometry and lignin abundance in Phragmites australis from a wetland system in China to better understand the biogeochemical cycling and C storage. Our data show that Si content (ranging between 0.202% to 6.614%) of Phragmites australis is negatively correlated with C concentration (38.150%–47.220%). Furthermore, Si content was negatively antagonistically related to the concentration of lignin-derived phenols in the stem (66.763–120.670 mg g-1 C) and sheath (65.400–114.118 mg g-1 C), but only a weak relationship was observed in the leaf tissue (36.439–55.905 mg g-1 C), which is relevant to the photosynthesis or stabilization function of the plant tissues. These results support the notion that biogenic Si (BSi) can substitute lignin as a structural component, due to their similar eco-physiological functions, reduces costs associated with lignin biosynthesis. The accumulation of BSi increased total biomass C storage and nutrient accumulation due to greater productivity of Phragmites australis. On the other hand, BSi regulated litter composition and quality (e.g. nutrient stoichiometry and lignin) that provide a possibility for the factors affecting litter decomposition. Thus competing processes (i.e. biomass quantity vs quality) can be influenced by Si cycling in wetlands. Abstract
Keane JB, Hoosbeek MR, Taylor CR, Miglietta F, Phoenix GK, Hartley IP
(2020). Soil C, N and P cycling enzyme responses to nutrient limitation under elevated CO2. BIOGEOCHEMISTRY
(2-3), 221-235. Author URL
(2019). A study of plant-soil-microbe interactions across contrasting treelines in the Peruvian Andes and sub-arctic Sweden.
A study of plant-soil-microbe interactions across contrasting treelines in the Peruvian Andes and sub-arctic Sweden
This dissertation addresses the question of how plant species shifts would impact carbon cycling in ecosystems, which are likely to soon and strongly be affected by climate change. Examples of such ecosystems are the high latitudes and the high altitudes, where the treeline ecotone can be an early indicator of changes in plant community composition. Biotic changes aboveground also modify belowground processes, particularly carbon (C) and nutrient cycling between plant roots and the assembled microbes. Plant-soil-microbe interactions were therefore studied across treelines in the Peruvian Andes and sub-arctic Sweden. Abstract
The first objective was to determine and compare the present soil C and nitrogen (N) stocks and vegetation characteristics through systematic study of a high altitudinal tropical and a sub-arctic treeline. This revealed higher soil C-stocks in the boreal region with potentially also higher microbial activity in summer. For both countries, organic soils were higher in C and N contents compared to the mineral soils. Soils were sampled from both soil horizons across respective treelines and taken to the laboratory to deepen the question of functionality. Microbial mineralisation of soil organic matter (SOM) was quantified in a microcosm soil incubation with addition of
substrates of different C:N ratios. Treatment C:N had negligible effect on SOM-mineralisation, which was reduced following substrate addition in the majority of incubations (negative priming). Mechanistically, this questions the N-mining hypothesis and suggests preferential substrate use. For the final data chapter, efforts were made to bring together all three compartments of soils, plants and microbes in vivo and study how their interactions mediate carbon and nutrient cycling between them. Negative rhizosphere priming was measured in most soils during the course of
the late growing season. This consistent result provides new insights to potential mechanisms of the finely tuned synchronisation of plant-soil-microbe interactions.
In the final discussion, these results were set into context to anticipate what could be done to further our understanding of ecosystem functioning at appropriate scales. Unravelling the interactions of plants, soils and microbes in more detail could help resolve the mechanisms of nutrient cycling and energy flows in different ecosystems and estimate the impact of climate change on the global carbon cycle with less uncertainty.
Gatis N, Benaud P, Ashe J, Luscombe D, Grand-Clement E, Hartley I, Anderson K, Brazier R
(2019). ASSESSING THE IMPACT OF PEAT EROSION ON GROWING SEASON CO2 FLUXES BY COMPARING EROSIONAL PEAT PANS AND SURROUNDING VEGETATED HAGGS. Wetlands Ecology and Management
ASSESSING THE IMPACT OF PEAT EROSION ON GROWING SEASON CO2 FLUXES BY COMPARING EROSIONAL PEAT PANS AND SURROUNDING VEGETATED HAGGS
Peatlands are recognised as an important but vulnerable ecological resource. Understanding the effects of existing damage, in this case erosion, enables more informed land management decisions to be made. Over the growing seasons of 2013 and 2014 photosynthesis and ecosystem respiration were measured using closed chamber techniques within vegetated haggs and erosional peat pans in Dartmoor National Park, southwest England. Below-ground total and heterotrophic respiration were measured and autotrophic respiration estimated from the vegetated haggs. Abstract
The mean water table was significantly higher in the peat pans than in the vegetated haggs; because of this, and the switching from submerged to dry peat, there were differences in vegetation composition, photosynthesis and ecosystem respiration. In the peat pans photosynthetic CO2 uptake and ecosystem respiration were greater than in the vegetated haggs and strongly dependent on the depth to water table (r2>0.78, p
Gatis NL, Benaud P, Ashe J, Luscombe D, Grand-Clement E, Hartley I, Anderson K, Brazier R (2019). Assessing the impact of peat erosion on growing season CO2 fluxes by comparing erosional peat pans and surrounding vegetated haggs (dataset).
Figueiredo Lugli L
(2019). Dynamics and biological interactions of phosphorus cycling in central Amazonian forests.
Dynamics and biological interactions of phosphorus cycling in central Amazonian forests
Soil nutrient availability is considered to constrain the productivity of terrestrial ecosystems, with phosphorus (P) considered to be the most limiting nutrient in tropical forests. Due the great importance of Amazon forests in carbon (C) cycling and the fact that the majority of Amazon forests grow in low-fertility soils, understanding how nutrient limitation may affect net primary productivity (NPP) in these ecosystems is crucial to predict C storage in response to future climate. The direct effects of nutrient limitation on above and belowground forest functioning can only be tested through experimentation and up to now, the few large scale fertilisation experiments installed in lowland tropical forests indicate that multiple nutrients may limit different aspects of tropical forests, with inconsistent evidence for P limitation. Since much less is known about the potential effects of nutrient limitation on belowground forest functioning, this research aimed to analyse the main belowground mechanisms involved in P cycling, and how roots and soil microorganisms adapt to different conditions of soil fertility in central Amazon forests. I investigated how root morphological traits, mycorrhizal colonisation as well as enzyme exudation both from roots and soil microbes were expressed in natural low-fertility soils and how these traits responded to the short-term addition of P, nitrogen (N) and cations, as part of the first large-scale soil nutrient manipulation experiment in a central Amazon lowland forest near Manaus, Brazil. I show that in natural low-fertility soils, roots display a range of adaptations to increase P-uptake efficiency and investments in root morphological and physiological adaptations as well as association with fungi symbionts are complementary towards maintaining forest productivity in a central Amazon forest. With nutrient addition, I found support for the hypothesis of P-limitation, since trees were able to rapidly adapt their root morphological traits, reduce investments in enzyme exudation and increase association with mycorrhizal fungi. Such responses were also affected by cation addition, reinforcing the idea that multiple nutrients may control the expression of root traits. The soil microbial community was also affected by the short-term addition of nutrients, with a reduction in enzyme production with the addition of phosphorus, indicating a rapid alleviation of phosphorus limitation, but this reduction was eliminated when cations were also added. My results suggest that plants and soil microorganisms can rapidly respond to changes in soil nutrient Abstract
availability by changing their investments in nutrient uptake mechanisms, ultimately impacting plant productivity. These responses are crucial if we are to better understand how these forests function and how they may respond to global change.
Gatis N, Grand-Clement E, Luscombe DJ, Hartley IP, Anderson K, Brazier RE
(2019). Growing season CO2 fluxes from a drained peatland dominated by Molinia caerulea. MIRES AND PEAT
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Tian J, Dungait JAJ, Lu X, Yang Y, Hartley IP, Zhang W, Mo J, Yu G, Zhou J, Kuzyakov Y, et al
(2019). Long-term nitrogen addition modifies microbial composition and functions for slow carbon cycling and increased sequestration in tropical forest soil. Glob Chang Biol
Long-term nitrogen addition modifies microbial composition and functions for slow carbon cycling and increased sequestration in tropical forest soil.
Nitrogen (N) deposition is a component of global change that has considerable impact on belowground carbon (C) dynamics. Plant growth stimulation and alterations of fungal community composition and functions are the main mechanisms driving soil C gains following N deposition in N-limited temperate forests. In N-rich tropical forests, however, N deposition generally has minor effects on plant growth; consequently, C storage in soil may strongly depend on the microbial processes that drive litter and soil organic matter decomposition. Here, we investigated how microbial functions in old-growth tropical forest soil responded to 13 years of N addition at four rates: 0 (Control), 50 (Low-N), 100 (Medium-N), and 150 (High-N) kg N ha-1 year-1. Soil organic carbon (SOC) content increased under High-N, corresponding to a 33% decrease in CO2 efflux, and reductions in relative abundances of bacteria as well as genes responsible for cellulose and chitin degradation. A 113% increase in N2 O emission was positively correlated with soil acidification and an increase in the relative abundances of denitrification genes (narG and norB). Soil acidification induced by N addition decreased available P concentrations, and was associated with reductions in the relative abundance of phytase. The decreased relative abundance of bacteria and key functional gene groups for C degradation were related to slower SOC decomposition, indicating the key mechanisms driving SOC accumulation in the tropical forest soil subjected to High-N addition. However, changes in microbial functional groups associated with N and P cycling led to coincidentally large increases in N2 O emissions, and exacerbated soil P deficiency. These two factors partially offset the perceived beneficial effects of N addition on SOC storage in tropical forest soils. These findings suggest a potential to incorporate microbial community and functions into Earth system models considering their effects on greenhouse gas emission, biogeochemical processes, and biodiversity of tropical ecosystems. Abstract
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Wu H, Lu L, Zhang Y, Xu C, Yang H, Zhou W, Wang W, Zhao L, He N, Smith MD, et al
(2019). Sediment addition and legume cultivation result in sustainable, long-term increases in ecosystem functions of sandy grasslands. LAND DEGRADATION & DEVELOPMENT
(14), 1667-1676. Author URL
Green SM, Dungait JAJ, Tu C, Buss HL, Sanderson N, Hawkes SJ, Xing K, Yue F, Hussey VL, Peng J, et al
(2019). Soil functions and ecosystem services research in the Chinese karst Critical Zone. Chemical Geology
Soil functions and ecosystem services research in the Chinese karst Critical Zone
Covering extensive parts of China, karst is a critically important landscape that has experienced rapid and intensive land use change and associated ecosystem degradation within only the last 50 years. In the natural state, key ecosystem services delivered by these landscapes include regulation of the hydrological cycle, nutrient cycling and supply, carbon storage in soils and biomass, biodiversity and food production. Intensification of agriculture since the late-20th century has led to a rapid deterioration in Critical Zone (CZ) state, evidenced by reduced crop production and rapid loss of soil. In many areas, an ecological ‘tipping point’ appears to have been passed as basement rock is exposed and ‘rocky desertification’ dominates. This paper reviews contemporary research of soil processes and ecosystems service delivery in Chinese karst ecosystems, with an emphasis on soil degradation and the potential for ecosystem recovery through sustainable management. It is clear that currently there is limited understanding of the geological, hydrological and ecological processes that control soil functions in these landscapes, which is critical for developing management strategies to optimise ecosystem service delivery. This knowledge gap presents a classic CZ scientific challenge because an integrated multi-disciplinary approach is essential to quantify the responses of soils in the Chinese karst CZ to extreme anthropogenic perturbation, to develop a mechanistic understanding of their resilience to environmental stressors, and thereby to inform strategies to recover and maintain sustainable soil function. Abstract
Hartley IP, Singh BK (2018). Chapter 8 Impact of Global Changes on Soil C Storage—Possible Mechanisms and Modeling Approaches. In (Ed) Soil Carbon Storage, 245-279.
Lopez-Sangil L, Hartley IP, Rovira P, Casals P, Sayer EJ
(2018). Drying and rewetting conditions differentially affect the mineralization of fresh plant litter and extant soil organic matter. Soil Biology and Biochemistry
Drying and rewetting conditions differentially affect the mineralization of fresh plant litter and extant soil organic matter
Drought is becoming more common globally and has the potential to alter patterns of soil carbon (C) storage in terrestrial ecosystems. After an extended dry period, a pulse of soil CO2 release is commonly observed upon rewetting (the so-called ‘Birch effect’), the magnitude of which depends on soil rewetting frequency. But the source and implications of this CO2 efflux are unclear. We used a mesocosm field experiment to subject agricultural topsoil to two distinct drying and rewetting frequencies, measuring Birch effects (as 3-day cumulative CO2 efflux upon rewetting) and the overall CO2 efflux over the entire drying-rewetting cycle. We used 14C-labelled wheat straw to determine the contribution of fresh (recently incorporated) plant litter or extant soil organic matter (SOM) to these fluxes, and assessed the extent to which the amount of soil microbial biomass + K2SO4-extractable organic C (fumigated-extracted C, FEC) before rewetting determined the magnitude of Birch effect CO2 pulses. Our results showed a gradual increase in SOM-derived organic solutes within the FEC fraction, and a decrease in soil microbial biomass, under more extreme drying and rewetting conditions. But, contrary to our hypothesis, pre-wetting levels of FEC were not related to the magnitude of the Birch effects. In the longer term, rewetting frequency and temperature influenced the overall (31-day cumulative) amount of CO2–C released from SOM upon rewetting, but the overall 14CO2–C respired from fresh straw was only influenced by the rewetting frequency, with no effect of seasonal temperature differences of ∼15 °C. We conclude that the mineralization of fresh plant litter in soils is more sensitive to water limitations than extant SOM in soils under drying-rewetting conditions. Moreover, we found little evidence to support the hypothesis that the availability of microbial and soluble organic C before rewetting determined the magnitude of the Birch effects, and suggest that future work should investigate whether these short-term CO2 pulses are predominantly derived from substrate-supply mechanisms resulting from the disruption of the soil organo-mineral matrix. Abstract
Hartley IP, Singh BK
(2018). Impact of global changes on soil C storage-possible mechanisms and modeling approaches. In (Ed) Soil Carbon Storage: Modulators, Mechanisms and Modeling
Impact of global changes on soil C storage-possible mechanisms and modeling approaches
Estop-Aragonés C, Cooper MDA, Fisher JP, Thierry A, Garnett MH, Charman DJ, Murton JB, Phoenix GK, Treharne R, Sanderson NK, et al
(2018). Limited release of previously-frozen C and increased new peat formation after thaw in permafrost peatlands. Soil Biology and Biochemistry
Limited release of previously-frozen C and increased new peat formation after thaw in permafrost peatlands
Permafrost stores globally significant amounts of carbon (C) which may start to decompose and be released to the atmosphere in form of carbon dioxide (CO2) and methane (CH4) as global warming promotes extensive thaw. This permafrost carbon feedback to climate is currently considered to be the most important carbon-cycle feedback missing from climate models. Predicting the magnitude of the feedback requires a better understanding of how differences in environmental conditions post-thaw, particularly hydrological conditions, control the rate at which C is released to the atmosphere. In the sporadic and discontinuous permafrost regions of north-west Canada, we measured the rates and sources of C released from relatively undisturbed ecosystems, and compared these with forests experiencing thaw following wildfire (well-drained, oxic conditions) and collapsing peat plateau sites (water-logged, anoxic conditions). Using radiocarbon analyses, we detected substantial contributions of deep soil layers and/or previously-frozen sources in our well-drained sites. In contrast, no loss of previously-frozen C as CO2 was detected on average from collapsed peat plateaus regardless of time since thaw and despite the much larger stores of available C that were exposed. Furthermore, greater rates of new peat formation resulted in these soils becoming stronger C sinks and this greater rate of uptake appeared to compensate for a large proportion of the increase in CH4 emissions from the collapse wetlands. We conclude that in the ecosystems we studied, changes in soil moisture and oxygen availability may be even more important than previously predicted in determining the effect of permafrost thaw on ecosystem C balance and, thus, it is essential to monitor, and simulate accurately, regional changes in surface wetness. Abstract
Quine T, Guo D, Green SM, Tu C, Hartley I, Zhang X, Dungait J, Wen X, Song Z, Liu H, et al
(2017). Ecosystem service delivery in Karst landscapes: anthropogenic perturbation and recovery. Acta Geochimica
Ecosystem service delivery in Karst landscapes: anthropogenic perturbation and recovery
Covering extensive parts of China, Karst landscapes are exceptional because rapid and intensive land use change has caused severe ecosystem degradation within only the last 50 years. The twentieth century intensification in food production through agriculture has led to a rapid deterioration of soil quality, evidenced in reduced crop production and rapid loss of soil. In many areas, a tipping point appears to have been passed as basement rock is exposed and ‘rocky desertification’ dominates. Through the establishment of the “Soil processes and ecological services in the karst critical zone of SW China” (SPECTRA) Critical Zone Observatory (CZO) we will endevaour to understand the fundmental processes involved in soil production and erosion, and investigate the integrated geophysical-geochemical-ecological responses of the CZ to perturbations. The CZ spans a gradient from undisturbed natural vegetation through human perturbed landscapes. We seek to understand the importance of heterogeneity in surface and below-ground morphology and flow pathways in determining the spatial distribution of key stocks (soil, C, vegetation, etc.) and their control on ecosystem service delivery. We will assess the extent to which the highly heterogeneous critical zone resources can be restored to enable sustainable delivery of ecosystem services. This paper presents the CZO design and initial assessment of soil and soil organic carbon stocks and evidence for their stability based on caesium-137 (137Cs) data. Abstract
Cooper MDA, Estop-Aragones C, Fisher JP, Thierry A, Garnett MH, Charman DJ, Murton JB, Phoenix GK, Treharne R, Kokelj SV, et al (2017). Limited contribution of permafrost carbon to
methane release from thawing peatlands. Nature Climate Change, 7, 507-511.
De Baets S, Van de Weg MJ, Lewis R, Steinberg N, Meersmans J, Quine TA, Shaver GR, Hartley IP
(2016). Investigating the controls on soil organic matter decomposition in tussock tundra soil and permafrost after fire. Soil Biology and Biochemistry
Investigating the controls on soil organic matter decomposition in tussock tundra soil and permafrost after fire
Rapid warming in Arctic ecosystems is resulting in increased frequency of disturbances such as fires, changes in the distribution and productivity of different plant communities, increasing thaw depths in permafrost soils and greater nutrient availability, especially nitrogen. Individually and collectively, these factors have the potential to strongly affect soil C decomposition rates, with implications for the globally significant stores of carbon in this region. However, considerable uncertainty remains regarding how C decomposition rates are controlled in Arctic soils. In this study we investigated how temperature, nitrogen availability and labile C addition affected rates of CO2 production in short (10-day for labile C) and long-term (1.5 year for temperature and N) incubations of samples collected from burned and unburned sites in the Anaktuvuk river burn on the North Slope of Alaska from different depths (organic horizon, mineral horizon and upper permafrost). The fire in this region resulted in the loss of several cms of the organic horizon and also increased active layer depth allowing the impacts of four years of thaw on deeper soil layers to be investigated. Respiration rates did not decline substantially during the long-term incubation, although decomposition rates per unit organic matter were greater in the organic horizon. In the mineral and upper permafrost soil horizons, CO2 production was more temperature sensitive, while N addition inhibited respiration in the mineral and upper permafrost layers, especially at low temperatures. In the short-term incubations, labile C additions promoted the decomposition of soil organic matter in the mineral and upper permafrost samples, but not in the organic samples, with this effect being lost following N addition in the deeper layers. These results highlight that (i) there are substantial amounts of labile organic matter in these soils (ii), the organic matter stored in mineral and upper permafrost in the tussock tundra is less readily decomposable than in the organic horizon, but that (iii) its decomposition is more sensitive to changes in temperature and that (iv) microbial activity in deeper soil layers is limited by labile C availability rather than N. Collectively, these results indicate that in addition to the loss of C by combustion of organic matter, increasing fire frequency also has the potential to indirectly promote the release of soil C to the atmosphere in the years following the disturbance. Abstract
Schädel C, Bader MK-F, Schuur EAG, Biasi C, Bracho R, Čapek P, De Baets S, Diáková K, Ernakovich J, Estop-Aragones C, et al (2016). Potential carbon emissions dominated by carbon dioxide from thawed permafrost soils. Nature Climate Change, 6(10), 950-953.
Green SM, Dungait J, Zhang X, Barrows T, Buss HL, Liu T, Hartley I, Song Z, Wen X, Liu H, et al (2016). SOIL PROCESSES AND ECOLOGICAL SERVICES IN THE KARST CRITICAL ZONE OF SW CHINA.
Auffret MD, Karhu K, Khachane A, Dungait JAJ, Fraser F, Hopkins DW, Wookey PA, Singh BK, Freitag TE, Hartley IP, et al
(2016). The Role of Microbial Community Composition in Controlling Soil Respiration Responses to Temperature. PLoS One
The Role of Microbial Community Composition in Controlling Soil Respiration Responses to Temperature.
Rising global temperatures may increase the rates of soil organic matter decomposition by heterotrophic microorganisms, potentially accelerating climate change further by releasing additional carbon dioxide (CO2) to the atmosphere. However, the possibility that microbial community responses to prolonged warming may modify the temperature sensitivity of soil respiration creates large uncertainty in the strength of this positive feedback. Both compensatory responses (decreasing temperature sensitivity of soil respiration in the long-term) and enhancing responses (increasing temperature sensitivity) have been reported, but the mechanisms underlying these responses are poorly understood. In this study, microbial biomass, community structure and the activities of dehydrogenase and β-glucosidase enzymes were determined for 18 soils that had previously demonstrated either no response or varying magnitude of enhancing or compensatory responses of temperature sensitivity of heterotrophic microbial respiration to prolonged cooling. The soil cooling approach, in contrast to warming experiments, discriminates between microbial community responses and the consequences of substrate depletion, by minimising changes in substrate availability. The initial microbial community composition, determined by molecular analysis of soils showing contrasting respiration responses to cooling, provided evidence that the magnitude of enhancing responses was partly related to microbial community composition. There was also evidence that higher relative abundance of saprophytic Basidiomycota may explain the compensatory response observed in one soil, but neither microbial biomass nor enzymatic capacity were significantly affected by cooling. Our findings emphasise the key importance of soil microbial community responses for feedbacks to global change, but also highlight important areas where our understanding remains limited. Abstract
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Fisher JP, Estop-Aragonés C, Thierry A, Charman DJ, Wolfe SA, Hartley IP, Murton JB, Williams M, Phoenix GK
(2016). The influence of vegetation and soil characteristics on active-layer thickness of permafrost soils in boreal forest. Glob Chang Biol
The influence of vegetation and soil characteristics on active-layer thickness of permafrost soils in boreal forest.
Carbon release from thawing permafrost soils could significantly exacerbate global warming as the active-layer deepens, exposing more carbon to decay. Plant community and soil properties provide a major control on this by influencing the maximum depth of thaw each summer (active-layer thickness; ALT), but a quantitative understanding of the relative importance of plant and soil characteristics, and their interactions in determine ALTs, is currently lacking. To address this, we undertook an extensive survey of multiple vegetation and edaphic characteristics and ALTs across multiple plots in four field sites within boreal forest in the discontinuous permafrost zone (NWT, Canada). Our sites included mature black spruce, burned black spruce and paper birch, allowing us to determine vegetation and edaphic drivers that emerge as the most important and broadly applicable across these key vegetation and disturbance gradients, as well as providing insight into site-specific differences. Across sites, the most important vegetation characteristics limiting thaw (shallower ALTs) were tree leaf area index (LAI), moss layer thickness and understory LAI in that order. Thicker soil organic layers also reduced ALTs, though were less influential than moss thickness. Surface moisture (0-6 cm) promoted increased ALTs, whereas deeper soil moisture (11-16 cm) acted to modify the impact of the vegetation, in particular increasing the importance of understory or tree canopy shading in reducing thaw. These direct and indirect effects of moisture indicate that future changes in precipitation and evapotranspiration may have large influences on ALTs. Our work also suggests that forest fires cause greater ALTs by simultaneously decreasing multiple ecosystem characteristics which otherwise protect permafrost. Given that vegetation and edaphic characteristics have such clear and large influences on ALTs, our data provide a key benchmark against which to evaluate process models used to predict future impacts of climate warming on permafrost degradation and subsequent feedback to climate. Abstract
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Hartley IP, Hill TC, Wade TJ, Clement RJ, Moncrieff JB, Prieto-Blanco A, Disney MI, Huntley B, Williams M, Howden NJK, et al
(2015). Quantifying landscape-level methane fluxes in subarctic Finland using a multiscale approach. Global Change Biology
Quantifying landscape-level methane fluxes in subarctic Finland using a multiscale approach
Quantifying landscape-scale methane (CH4) fluxes from boreal and arctic regions, and determining how they are controlled, is critical for predicting the magnitude of any CH4 emission feedback to climate change. Furthermore, there remains uncertainty regarding the relative importance of small areas of strong methanogenic activity, vs. larger areas with net CH4 uptake, in controlling landscape-level fluxes. We measured CH4 fluxes from multiple microtopographical subunits (sedge-dominated lawns, interhummocks and hummocks) within an aapa mire in subarctic Finland, as well as in drier ecosystems present in the wider landscape, lichen heath and mountain birch forest. An intercomparison was carried out between fluxes measured using static chambers, up-scaled using a high-resolution landcover map derived from aerial photography and eddy covariance. Strong agreement was observed between the two methodologies, with emission rates greatest in lawns. CH4 fluxes from lawns were strongly related to seasonal fluctuations in temperature, but their floating nature meant that water-table depth was not a key factor in controlling CH4 release. In contrast, chamber measurements identified net CH4 uptake in birch forest soils. An intercomparison between the aerial photography and satellite remote sensing demonstrated that quantifying the distribution of the key CH4 emitting and consuming plant communities was possible from satellite, allowing fluxes to be scaled up to a 100 km2 area. For the full growing season (May to October), ~ 1.1-1.4 g CH4 m-2 was released across the 100 km2 area. This was based on up-scaled lawn emissions of 1.2-1.5 g CH4 m-2, vs. an up-scaled uptake of 0.07-0.15 g CH4 m-2 by the wider landscape. Given the strong temperature sensitivity of the dominant lawn fluxes, and the fact that lawns are unlikely to dry out, climate warming may substantially increase CH4 emissions in northern Finland, and in aapa mire regions in general. Abstract
Laudicina VA, Benhua S, Dennis PG, Badalucco L, Rushton SP, Newsham KK, O’Donnell AG, Hartley IP, Hopkins DW
(2015). Responses to increases in temperature of heterotrophic micro-organisms in soils from the maritime Antarctic. Polar Biology
Responses to increases in temperature of heterotrophic micro-organisms in soils from the maritime Antarctic
Understanding relationships between environmental changes and soil microbial respiration is critical for predicting changes in soil organic carbon (SOC) fluxes and content. The maritime Antarctic is experiencing one of the fastest rates of warming in the world and is therefore a key location to examine the effect of temperature on SOC mineralization by the respiration of soil micro-organisms. However, depletion of the labile substrates at higher temperatures relative to the total SOC and greater temperature sensitivity of recalcitrant components of the SOC confound simple interpretations of the effects of warming. We have addressed these issues by testing the hypothesis that respiration by heterotrophic soil micro-organisms is not down-regulated with increasing temperature by comparing the increase in biomass-specific respiration rate with temperature to the increase in respiration rate per unit SOC. We used five soils from the maritime Antarctic ranging in latitude and SOC content and measured the soil respiratory responses to temperatures ranging from 2 to 50 °C in laboratory incubations lasting up to 31 days. In all cases, soil respiration increased with temperature up to 50 °C, even though this exceeds the temperatures normally be experienced, indicating that the community contained sufficient physiological diversity to be able to respire over large temperature ranges. Both the biomass-specific respiration rate and the overall rate of SOC mineralization increased with temperature, which we interpret as respiration by soil micro-organisms not down-regulating relative to temperature. Abstract
Hartley IP (2014). Soil carbon: Resisting climate change. Nature Climate Change, 4(9), 760-761.
Karhu K, Auffret MD, Dungait JAJ, Hopkins DW, Prosser JI, Singh BK, Subke J-A, Wookey PA, Agren GI, Sebastià M-T, et al
(2014). Temperature sensitivity of soil respiration rates enhanced by microbial community response. Nature
Temperature sensitivity of soil respiration rates enhanced by microbial community response.
Soils store about four times as much carbon as plant biomass, and soil microbial respiration releases about 60 petagrams of carbon per year to the atmosphere as carbon dioxide. Short-term experiments have shown that soil microbial respiration increases exponentially with temperature. This information has been incorporated into soil carbon and Earth-system models, which suggest that warming-induced increases in carbon dioxide release from soils represent an important positive feedback loop that could influence twenty-first-century climate change. The magnitude of this feedback remains uncertain, however, not least because the response of soil microbial communities to changing temperatures has the potential to either decrease or increase warming-induced carbon losses substantially. Here we collect soils from different ecosystems along a climate gradient from the Arctic to the Amazon and investigate how microbial community-level responses control the temperature sensitivity of soil respiration. We find that the microbial community-level response more often enhances than reduces the mid- to long-term (90 days) temperature sensitivity of respiration. Furthermore, the strongest enhancing responses were observed in soils with high carbon-to-nitrogen ratios and in soils from cold climatic regions. After 90 days, microbial community responses increased the temperature sensitivity of respiration in high-latitude soils by a factor of 1.4 compared to the instantaneous temperature response. This suggests that the substantial carbon stores in Arctic and boreal soils could be more vulnerable to climate warming than currently predicted. Abstract
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Hartley I, Garnett MH, Sommerkorn M, Hopkins DW, Fletcher BJ, Sloan VL, Phoenix GK, Wookey PA (2013). A potential loss of carbon associated with greater
plant growth in the European Arctic. Nature Climate Change, 2, 875-879.
Fraser FC, Hallett PD, Wookey PA, Hartley IP, Hopkins DW
(2013). How do enzymes catalysing soil nitrogen transformations respond to changing temperatures?. Biology and Fertility of Soils
How do enzymes catalysing soil nitrogen transformations respond to changing temperatures?
Biological processes in soils are regulated in part by soil temperature, and there is currently considerable interest in obtaining robust information on the temperature sensitivity of carbon cycling process. However, very little comparable information exists on the temperature regulation of specific nitrogen cycling processes. This paper addresses this problem by measuring the temperature sensitivity of nitrogen cycling enzymes in soil. A grassland soil was incubated over a range of temperatures (-2 to 21 °C) reflecting 99 % of the soil temperature range during the previous 50 years at the site. After 7 and 14 days of incubation, potential activities of protease, amidase and urease were determined. Activities of protease and urease were positively related to temperature (activation energy; Ea = 49. 7 and 73. 4 kJ mol-1, respectively, and Q10 = 2. 97 and 2. 78, respectively). By contrast, amidase activity was relatively insensitive to temperature, but the activity was significantly increased after the addition of glucose. This indicated that there was a stoichiometric imbalance with amidase activity only being triggered when there was a supply of exogenous carbon. Thus, carbon supply was a greater constraint to amidase activity than temperature was in this particular soil. © 2012 Springer-Verlag. Abstract
Hartley IP, Garnett MH, Sommerkorn M, Hopkins DW, Wookey PA
(2013). The age of CO<inf>2</inf> released from soils in contrasting ecosystems during the arctic winter. Soil Biology and Biochemistry
The age of CO2 released from soils in contrasting ecosystems during the arctic winter
In arctic ecosystems, winter soil respiration can contribute substantially to annual CO2 release, yet the source of this C is not clear. We analysed the 14C content of C released from plant-free plots in mountain birch forest and tundra-heath. Winter-respired CO2 was found to be a similar age (tundra) or older (forest) than C released during the previous autumn. Overall, our study demonstrates that the decomposition of older C can continue during the winter, in these two contrasting arctic ecosystems. copy; 2013 Elsevier Ltd. Abstract
Burke EJ, Hartley I, Jones CD (2012). Uncertainties in the global temperature change caused by carbon
release from permafrost thawing. The Cryosphere, 6, 1063-1076.
Burke EJ, Hartley IP, Jones CD (2012). Uncertainties in the global temperature change caused by carbon release from permafrost thawing. , 6(2), 1367-1404.
Garnett MH, Hartley IP
(2010). A passive sampling method for radiocarbon analysis of atmospheric CO<inf>2</inf> using molecular sieve. Atmospheric Environment
A passive sampling method for radiocarbon analysis of atmospheric CO2 using molecular sieve
Radiocarbon (14C) analysis of atmospheric CO2 can provide information on CO2 sources and is potentially valuable for validating inventories of fossil fuel-derived CO2 emissions to the atmosphere. We tested zeolite molecular sieve cartridges, in both field and laboratory experiments, for passively collecting atmospheric CO2. Cartridges were exposed to the free atmosphere in two configurations which controlled CO2 trapping rate, allowing collection of sufficient CO2 in between 1.5 and 10 months at current levels. 14C results for passive samples were within measurement uncertainty of samples collected using a pump-based system, showing that the method collected samples with 14C contents representative of the atmosphere. δ13C analysis confirmed that the cartridges collected representative CO2 samples, however, fractionation during passive trapping means that δ13C values need to be adjusted by an amount which we have quantified. Trapping rate was proportional to atmospheric CO2 concentration, and was not affected by exposure time unless this exceeded a threshold. Passive sampling using molecular sieve cartridges provides an easy and reliable method to collect atmospheric CO2 for 14C analysis. © 2009 Elsevier Ltd. All rights reserved. Abstract
Hartley IP, Hopkins DW, Sommerkorn M, Wookey PA
(2010). The response of organic matter mineralisation to nutrient and substrate additions in sub-arctic soils. Soil Biology and Biochemistry
The response of organic matter mineralisation to nutrient and substrate additions in sub-arctic soils
Global warming in the Arctic may alter decomposition rates in Arctic soils and therefore nutrient availability. In addition, changes in the length of the growing season may increase plant productivity and the rate of labile C input below ground. We carried out an experiment in which inorganic nutrients (NH4NO3 and NaPO4) and organic substrates (glucose and glycine) were added to soils sampled from across the mountain birch forest-tundra heath ecotone in northern Sweden (organic and mineral soils from the forest, and organic soil only from the heath). Carbon dioxide production was then monitored continuously over the following 19 days. Neither inorganic N nor P additions substantially affected soil respiration rates when added separately. However, combined N and P additions stimulated microbial activity, with the response being greatest in the birch forest mineral soil (57% increase in CO2 production compared with 26% in the heath soil and 8% in the birch forest organic soil). Therefore, mineralisation rates in these soils may be stimulated if the overall nutrient availability to microbes increases in response to global change, but N deposition alone is unlikely to enhance decomposition. Adding either, or both, glucose and glycine increased microbial respiration. Isotopic separation indicated that the mineralisation of native soil organic matter (SOM) was stimulated by glucose addition in the heath soil and the forest mineral soil, but not in the forest organic soil. These positive 'priming' effects were lost following N addition in forest mineral soil, and following both N and P additions in the heath soil. In order to meet enhanced microbial nutrient demand, increased inputs of labile C from plants could stimulate the mineralisation of SOM, with the soil C stocks in the tundra-heath potentially most vulnerable. © 2009 Elsevier Ltd. All rights reserved. Abstract
Garnett MH, Hartley IP, Hopkins DW, Sommerkorn M, Wookey PA
(2009). A passive sampling method for radiocarbon analysis of soil respiration using molecular sieve. Soil Biology and Biochemistry
A passive sampling method for radiocarbon analysis of soil respiration using molecular sieve
Radiocarbon analysis of soil CO2 can provide information on the age, source and turnover rate of soil organic C. We developed a new method for passively trapping respired CO2 on molecular sieve, allowing it to be returned to the laboratory and recovered for C isotope analysis. We tested the method on a soil at a grassland site, and using a synthetic soil created to provide a contrasting isotopic signature. As with other passive sampling techniques, a small amount of fractionation of the 13C isotope occurs during sampling, which we have quantified, otherwise the results show that the molecular sieve traps a sufficiently large and representative sample of CO2 for C isotope analysis. Since 14C results are routinely corrected for mass-dependent fractionation, our results show that passive sampling of soil respiration using molecular sieve offers a reliable method to collect soil-respired CO2 for 14C analysis. © 2009 Elsevier Ltd. All rights reserved. Abstract
Wookey PA, Aerts R, Bardgett RD, Baptist F, Bråthen K, Cornelissen JHC, Gough L, Hartley IP, Hopkins DW, Lavorel S, et al
(2009). Ecosystem feedbacks and cascade processes: Understanding their role in the responses of Arctic and alpine ecosystems to environmental change. Global Change Biology
Ecosystem feedbacks and cascade processes: Understanding their role in the responses of Arctic and alpine ecosystems to environmental change
Global environmental change, related to climate change and the deposition of airborne N-containing contaminants, has already resulted in shifts in plant community composition among plant functional types in Arctic and temperate alpine regions. In this paper, we review how key ecosystem processes will be altered by these transformations, the complex biological cascades and feedbacks that might result, and some of the potential broader consequences for the earth system. Firstly, we consider how patterns of growth and allocation, and nutrient uptake, will be altered by the shifts in plant dominance. The ways in which these changes may disproportionately affect the consumer communities, and rates of decomposition, are then discussed. We show that the occurrence of a broad spectrum of plant growth forms in these regions (from cryptogams to deciduous and evergreen dwarf shrubs, graminoids and forbs), together with hypothesized low functional redundancy, will mean that shifts in plant dominance result in a complex series of biotic cascades, couplings and feedbacks which are supplemental to the direct responses of ecosystem components to the primary global change drivers. The nature of these complex interactions is highlighted using the example of the climate-driven increase in shrub cover in low-Arctic tundra, and the contrasting transformations in plant functional composition in mid-latitude alpine systems. Finally, the potential effects of the transformations on ecosystem properties and processes that link with the earth system are reviewed. We conclude that the effects of global change on these ecosystems, and potential climate-change feedbacks, cannot be predicted from simple empirical relationships between processes and driving variables. Rather, the effects of changes in species distributions and dominances on key ecosystem processes and properties must also be considered, based upon best estimates of the trajectories of key transformations, their magnitude and rates of change. © Journal compilation © 2009 Blackwell Publishing. Abstract
Hartley IP, Hopkins DW, Garnett MH, Sommerkorn M, Wookey PA
(2009). No evidence for compensatory thermal adaptation of soil microbial respiration in the study of Bradford et al. (2008). Ecol Lett
No evidence for compensatory thermal adaptation of soil microbial respiration in the study of Bradford et al. (2008).
Bradford et al. (2008) conclude that thermal adaptation will reduce the response of soil microbial respiration to rising global temperatures. However, we question both the methods used to calculate mass-specific respiration rates and the interpretation of the results. No clear evidence of thermal adaptation reducing soil microbial activity was produced. Abstract
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(2008). Arctic soils face the big thaw. Planet Earth
Arctic soils face the big thaw
Soils from Arctic Sweden have been collected to investigate how this type of soil respond to warming. Arctic soils are interesting as they contain lots of carbon and are expected to warm rapidly. Unusually, researchers cooled down the soil. This action reduces microscopic organisms' activity but the acclimatization also increases respiration rates. This is probably due to soil microbes adapting to colder temperatures by reducing activity. This research suggests that carbon release from the world's coldest soils could contribute disproportionately to a soil-driven acceleration of climate change and that temperature controls carbon loss from Arctic soils. Abstract
Zaragoza-Castells J, Sánchez-Gómez D, Hartley IP, Matesanz S, Valladares F, Lloyd J, Atkin OK
(2008). Climate-dependent variations in leaf respiration in a dry-land, low productivity Mediterranean forest: the importance of acclimation in both high-light and shaded habitats. Functional Ecology
Climate-dependent variations in leaf respiration in a dry-land, low productivity Mediterranean forest: the importance of acclimation in both high-light and shaded habitats
1. Climate-driven changes in leaf respiration (R) in darkness have the potential to determine whether low productivity ecosystems exhibit positive or negative carbon balances. 2. We investigated whether sustained exposure to full sunlight, shade and seasonal drought alters the temperature response of leaf R of field-grown Quercus ilex subsp. ballota in a dry-land continental Mediterranean ecosystem. The plants studied, experience large diurnal and seasonal variations in temperature. 3. Whilst growth irradiance impacted on photosynthesis, it had little effect on the short-term temperature dependence of leaf R. Moreover, although basal rates of leaf R (i.e. rates of R at a common measuring temperature) were higher in sun-exposed than shade-exposed leaves, growth irradiance had little impact on the degree of acclimation to seasonal changes in temperature and/or moisture. Basal rates of leaf R were higher in winter than summer in both sun-exposed and shaded plants. Estimated Q 10 values (i.e. proportional increase in R per 10 °C rise in temperature) for leaf R were greater in winter than summer; however, no seasonal variation was found in the apparent activation energy (E0) of leaf R. These observations were used to construct a simple Arrhenius model that fully accounted for both daily and seasonal variations in the temperature dependence of R in both sun-exposed and shaded plants. Crucial to the model was accounting for the seasonal and irradiance-dependent shifts in the basal rate of leaf R. 4. Although the balance between daily R and photosynthesis increased markedly in summer (particularly under full sun), the increase in this ratio was markedly less than would have been the case if leaf R had not acclimated to the high average day time temperatures in summer. 5. It is concluded that seasonal acclimation of leaf R plays a crucial role in determining the viability of tree growth in dry-land, low productivity forest ecosystems. © 2007 the Authors. Abstract
Hartley IP, Hopkins DW, Garnett MH, Sommerkorn M, Wookey PA
(2008). Soil microbial respiration in arctic soil does not acclimate to temperature. Ecol Lett
Soil microbial respiration in arctic soil does not acclimate to temperature.
Warming-induced release of CO2 from the large carbon (C) stores in arctic soils could accelerate climate change. However, declines in the response of soil respiration to warming in long-term experiments suggest that microbial activity acclimates to temperature, greatly reducing the potential for enhanced C losses. As reduced respiration rates with time could be equally caused by substrate depletion, evidence for thermal acclimation remains controversial. To overcome this problem, we carried out a cooling experiment with soils from arctic Sweden. If acclimation causes the reduction in soil respiration observed after experimental warming, then it should subsequently lead to an increase in respiration rates after cooling. We demonstrate that thermal acclimation did not occur following cooling. Rather, during the 90 days after cooling, a further reduction in the soil respiration rate was observed, which was only reversed by extended re-exposure to warmer temperatures. We conclude that over the time scale of a few weeks to months, warming-induced changes in the microbial community in arctic soils will amplify the instantaneous increase in the rates of CO2 production and thus enhance C losses potentially accelerating the rate of 21st century climate change. Abstract
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Hawkes CV, Hartley IP, Ineson P, Fitter AH
(2008). Soil temperature affects carbon allocation within arbuscular mycorrhizal networks and carbon transport from plant to fungus. Global Change Biology
Soil temperature affects carbon allocation within arbuscular mycorrhizal networks and carbon transport from plant to fungus
How soil carbon balance will be affected by plant-mycorrhizal interactions under future climate scenarios remains a significant unknown in our ability to forecast ecosystem carbon storage and fluxes. We examined the effects of soil temperature (14, 20, 26 °C) on the structure and extent of a multispecies community of arbuscular mycorrhizal (AM) fungi associated with Plantago lanceolata. To isolate fungi from roots, we used a mesh-divided pot system with separate hyphal compartments near and away from the plant. A 13C pulse label was then used to trace the flow of recently fixed photosynthate from plants into belowground pools and respiration. Temperature significantly altered the structure and allocation of the AM hyphal network, with a switch from more vesicles (storage) in cooled soils to more extensive extraradical hyphal networks (growth) in warmed soils. As soil temperature increased, we also observed an increase in the speed at which plant photosynthate was transferred to and respired by roots and AM fungi coupled with an increase in the amount of carbon respired per unit hyphal length. These differences were largely independent of plant size and rates of photosynthesis. In a warmer world, we would therefore expect more carbon losses to the atmosphere from AM fungal respiration, which are unlikely to be balanced by increased growth of AM fungal hyphae. © 2008 the Authors Journal compilation © 2008 Blackwell Publishing Ltd. Abstract
Hartley IP, Ineson P
(2008). Substrate quality and the temperature sensitivity of soil organic matter decomposition. Soil Biology and Biochemistry
Substrate quality and the temperature sensitivity of soil organic matter decomposition
Determining the relative temperature sensitivities of the decomposition of the different soil organic matter (SOM) pools is critical for predicting the long-term impacts of climate change on soil carbon (C) storage. Although kinetic theory suggests that the temperature sensitivity of SOM decomposition should increase with substrate recalcitrance, there remains little empirical evidence to support this hypothesis. In the study presented here, sub-samples from a single bulk soil sample were frozen and sequentially defrosted to produce samples of the same soil that had been incubated for different lengths of time, up to a maximum of 124 days. These samples were then placed into an incubation system which allowed CO2 production to be monitored constantly and the response of soil respiration to short-term temperature manipulations to be investigated. The temperature sensitivity of soil CO2 production increased significantly with incubation time suggesting that, as the most labile SOM pool was depleted the temperature sensitivity of SOM decomposition increased. This study is therefore one of the first to provide empirical support for kinetic theory. Further, using a modelling approach, we demonstrate that it is the temperature sensitivity of the decomposition of the more recalcitrant SOM pools that will determine long-term soil-C losses. Therefore, the magnitude of the positive feedback to global warming may have been underestimated in previous modelling studies. © 2008 Elsevier Ltd. All rights reserved. Abstract
Hartley IP, Heinemeyer A, Ineson P
(2007). Effects of three years of soil warming and shading on the rate of soil respiration: Substrate availability and not thermal acclimation mediates observed response. Global Change Biology
Effects of three years of soil warming and shading on the rate of soil respiration: Substrate availability and not thermal acclimation mediates observed response
In a number of recent field studies, the positive response of soil respiration to warming has been shown to decline over time. The two main differing hypotheses proposed to explain these results are: (1) soil microbial respiration acclimates to the increased temperature, and (2) substrate availability within the soil decreases with warming so reducing the rate of soil respiration. To investigate the relative merits of these two hypotheses, soil samples (both intact cores and sieved samples) from a 3-year grassland soil-warming and shading experiment were incubated for 4 weeks at three different temperatures under constant laboratory conditions. We tested the hypothesis that sieving the soils would reduce differences in substrate availability between warmed and control plot samples and would therefore result in similar respiration rates if microbial activity had not acclimated to soil warming. In addition, to further test the effect of substrate availability, we compared the respiration rates of soils taken from shaded and unshaded plots. Both soil warming and shading significantly reduced respiration rates in the intact cores, especially under higher incubation temperatures. However, sieving the soil greatly reduced these differences suggesting that substrate availability, and not microbial acclimation to the higher temperatures, played the dominant role in determining the response of heterotrophic soil respiration to warming. The effect of shading appeared to be mediated by reduced plant productivity affecting substrate availability within the soil and hence microbial activity. Given the lack of evidence for thermal acclimation of microbial respiration, there remains the potential for prolonged carbon losses from soils in response to warming. © 2007 Blackwell Publishing Ltd. Abstract
Heinemeyer A, Hartley IP, Evans SP, Carreira De La Fuente JA, Ineson P
(2007). Forest soil CO<inf>2</inf> flux: Uncovering the contribution and environmental responses of ectomycorrhizas. Global Change Biology
Forest soil CO2 flux: Uncovering the contribution and environmental responses of ectomycorrhizas
Forests play a critical role in the global carbon cycle, being considered an important and continuing carbon sink. However, the response of carbon sequestration in forests to global climate change remains a major uncertainty, with a particularly poor understanding of the origins and environmental responses of soil CO2 efflux. For example, despite their large biomass, the contribution of ectomycorrhizal (EM) fungi to forest soil CO2 efflux and responses to changes in environmental drivers has, to date, not been quantified in the field. Their activity is often simplistically included in the 'autotrophic' root respiration term. We set up a multiplexed continuous soil respiration measurement system in a young Lodgepole pine forest, using a mycorrhizal mesh collar design, to monitor the three main soil CO2 efflux components: root, extraradical mycorrhizal hyphal, and soil heterotrophic respiration. Mycorrhizal hyphal respiration increased during the first month after collar insertion and thereafter remained remarkably stable. During autumn the soil CO2 flux components could be divided into ∼60% soil heterotrophic, ∼25% EM hyphal, and ∼15% root fluxes. Thus the extraradical EM mycelium can contribute substantially more to soil CO2 flux than do roots. While EM hyphal respiration responded strongly to reductions in soil moisture and appeared to be highly dependent on assimilate supply, it did not responded directly to changes in soil temperature. It was mainly the soil heterotrophic flux component that caused the commonly observed exponential relationship with temperature. Our results strongly suggest that accurate modelling of soil respiration, particularly in forest ecosystems, needs to explicitly consider the mycorrhizal mycelium and its dynamic response to specific environmental factors. Moreover, we propose that in forest ecosystems the mycorrhizal CO2 flux component represents an overflow 'CO2 tap' through which surplus plant carbon may be returned directly to the atmosphere, thus limiting expected carbon sequestration from trees under elevated CO2. © 2007 Blackwell Publishing Ltd. Abstract
Hartley IP, Heinemeyer A, Evans SP, Ineson P
(2007). The effect of soil warming on bulk soil vs. rhizosphere respiration. Global Change Biology
The effect of soil warming on bulk soil vs. rhizosphere respiration
There has been considerable debate on whether root/rhizosphere respiration or bulk soil respiration is more sensitive to long-term temperature changes. We investigated the response of belowground respiration to soil warming by 3 °C above ambient in bare soil plots and plots planted with wheat and maize. Initially, belowground respiration responded more to the soil warming in bare soil plots than in planted plots. However, as the growing season progressed, a greater soil-warming response developed in the planted plots as the contribution of root/rhizosphere respiration to belowground respiration declined. A negative correlation was observed between the contribution of root/ rhizosphere respiration to total belowground respiration and the magnitude of the soil-warming response indicating that bulk soil respiration is more temperature sensitive than root/rhizosphere respiration. The dependence of root/rhizosphere respiration on substrate provision from photosynthesis is the most probable explanation for the observed lower temperature sensitivity of root/rhizosphere respiration. At harvest in late September, final crop biomass did not differ between the two soil temperature treatments in either the maize or wheat plots. Postharvest, flux measurements during the winter months indicated that the response of belowground respiration to the soil-warming treatment increased in magnitude (response equated to a Q10 value of 5.7 compared with ∼2.3 during the growing season). However, it appeared that this response was partly caused by a strong indirect effect of soil warming. When measurements were made at a common temperature, belowground respiration remained higher in the warmed subplots suggesting soil warming had maintained a more active microbial community through the winter months. It is proposed that any changes in winter temperatures, resulting from global warming, could alter the sink strength of terrestrial ecosystems considerably. © 2007 Blackwell Publishing Ltd. Abstract
Hartley IP, Armstrong AF, Murthy R, Barron-Gafford G, Ineson P, Atkin OK
(2006). The dependence of respiration on photosynthetic substrate supply and temperature: Integrating leaf, soil and ecosystem measurements. Global Change Biology
The dependence of respiration on photosynthetic substrate supply and temperature: Integrating leaf, soil and ecosystem measurements
Interactions between photosynthetic substrate supply and temperature in determining the rate of three respiration components (leaf, belowground and ecosystem respiration) were investigated within three environmentally controlled, Populus deltoides forest bays at Biosphere 2, Arizona. Over 2 months, the atmospheric CO2 concentration and air temperature were manipulated to test the following hypotheses: (1) the responses of the three respiration components to changes in the rate of photosynthesis would differ both in speed and magnitude; (2) the temperature sensitivity of leaf and belowground respiration would increase in response to a rise in substrate availability; and, (3) at the ecosystem level, the ratio of respiration to photosynthesis would be conserved despite week-to-week changes in temperature. All three respiration rates responded to the CO2 concentration-induced changes in photosynthesis. However, the proportional change in the rate of leaf respiration was more than twice that of belowground respiration and, when photosynthesis was reduced, was also more rapid. The results suggest that aboveground respiration plays a key role in the overall response of ecosystem respiration to short-term changes in canopy photosynthesis. The short-term temperature sensitivity of leaf respiration, measured within a single night, was found to be affected more by developmental conditions than photosynthetic substrate availability, as the Q10 was lower in leaves that developed at high CO2, irrespective of substrate availability. However, the temperature sensitivity of belowground respiration, calculated between periods of differing air temperature, appeared to be positively correlated with photosynthetic substrate availability. At the ecosystem level, respiration and photosynthesis were positively correlated but the relationship was affected by temperature; for a given rate of daytime photosynthesis, the rate of respiration the following night was greater at 25 than 20°C. This result suggests that net ecosystem exchange did not acclimate to temperature changes lasting up to 3 weeks. Overall, the results of this study demonstrate that the three respiration terms differ in their dependence on photosynthesis and that, short- and medium-term changes in temperature may affect net carbon storage in terrestrial ecosystems. © 2006 Blackwell Publishing Ltd. Abstract