Responses of ecosystem carbon cycle to experimental warming: a meta‐analysis
TL;DR: It is demonstrated that the stimulation of plant-derived C influx basically offset the increase in warming-induced efflux and resulted in insignificant changes in litter and soil C content, indicating that climate warming may not trigger strong positive C-climate feedback from terrestrial ecosystems.
Abstract: Global warming potentially alters the terrestrial carbon (C) cycle, likely feeding back to further climate warming. However, how the ecosystem C cycle responds and feeds back to warming remains unclear. Here we used a meta-analysis approach to quantify the response ratios of 18 variables of the ecosystem C cycle to experimental warming and evaluated ecosystem C-cycle feedback to climate warming. Our results showed that warming stimulated gross ecosystem photosynthesis (GEP) by 15.7%, net primary production (NPP) by 4.4%, and plant C pools from above- and belowground parts by 6.8% and 7.0%, respectively. Experimental warming accelerated litter mass loss by 6.8%, soil respiration by 9.0%, and dissolved organic C leaching by 12.1%. In addition, the responses of some of those variables to experimental warming differed among the ecosystem types. Our results demonstrated that the stimulation of plant-derived C influx basically offset the increase in warming-induced efflux and resulted in insignificant changes in litter and soil C content, indicating that climate warming may not trigger strong positive C-climate feedback from terrestrial ecosystems. Moreover, the increase in plant C storage together with the slight but not statistically significant decrease of net ecosystem exchange (NEE) across ecosystems suggests that terrestrial ecosystems might be a weak C sink rather than a C source under global climate warming. Our results are also potentially useful for parameterizing and benchmarking land surface models in terms of C cycle responses to climate warming.
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Pacific Northwest National Laboratory1, Yale University2, National Center for Atmospheric Research3, Marine Biological Laboratory4, Colorado State University5, Wageningen University and Research Centre6, University of California, Irvine7, Kansas State University8, University of Oregon9, Michigan Technological University10, University of Sydney11, University of Minnesota12, Duke University13, University of Tennessee14, University of Copenhagen15, Spanish National Research Council16, University of New Hampshire17, Northeast Normal University18, University of California, Berkeley19, University of Oklahoma20, Hungarian Academy of Sciences21, Swedish University of Agricultural Sciences22, University of Manchester23, Tsinghua University24, National University of Singapore25, Chinese Academy of Sciences26, University of Hohenheim27, University of Georgia28, Hampshire College29, Boston University30, University of Alaska Anchorage31
TL;DR: In this article, the authors present a comprehensive analysis of warming-induced changes in soil carbon stocks by assembling data from 49 field experiments located across North America, Europe and Asia, and provide estimates of soil carbon sensitivity to warming that may help to constrain Earth system model projections.
Abstract: The majority of the Earth's terrestrial carbon is stored in the soil. If anthropogenic warming stimulates the loss of this carbon to the atmosphere, it could drive further planetary warming. Despite evidence that warming enhances carbon fluxes to and from the soil, the net global balance between these responses remains uncertain. Here we present a comprehensive analysis of warming-induced changes in soil carbon stocks by assembling data from 49 field experiments located across North America, Europe and Asia. We find that the effects of warming are contingent on the size of the initial soil carbon stock, with considerable losses occurring in high-latitude areas. By extrapolating this empirical relationship to the global scale, we provide estimates of soil carbon sensitivity to warming that may help to constrain Earth system model projections. Our empirical relationship suggests that global soil carbon stocks in the upper soil horizons will fall by 30 ± 30 petagrams of carbon to 203 ± 161 petagrams of carbon under one degree of warming, depending on the rate at which the effects of warming are realized. Under the conservative assumption that the response of soil carbon to warming occurs within a year, a business-as-usual climate scenario would drive the loss of 55 ± 50 petagrams of carbon from the upper soil horizons by 2050. This value is around 12-17 per cent of the expected anthropogenic emissions over this period. Despite the considerable uncertainty in our estimates, the direction of the global soil carbon response is consistent across all scenarios. This provides strong empirical support for the idea that rising temperatures will stimulate the net loss of soil carbon to the atmosphere, driving a positive land carbon-climate feedback that could accelerate climate change.
787 citations
Peking University1, Chinese Academy of Sciences2, University of Exeter3, Centre national de la recherche scientifique4, Lund University5, Max Planck Society6, National Center for Atmospheric Research7, Beijing Normal University8, University of Sheffield9, Fudan University10, University of Oklahoma11, Boston University12, University of Maryland, College Park13
TL;DR: Carbon-nitrogen interactions significantly influence the simulated response of carbon cycle to temperature and atmospheric CO2 concentration, suggesting that nutrients limitations should be included in the next generation of terrestrial biosphere models.
Abstract: The purpose of this study was to evaluate 10 process-based terrestrial biosphere models that were used for the IPCC fifth Assessment Report. The simulated gross primary productivity (GPP) is compared with flux-tower-based estimates by Jung et al. [Journal of Geophysical Research 116 (2011) G00J07] (JU11). The net primary productivity (NPP) apparent sensitivity to climate variability and atmospheric CO2 trends is diagnosed from each model output, using statistical functions. The temperature sensitivity is compared against ecosystem field warming experiments results. The CO2 sensitivity of NPP is compared to the results from four Free-Air CO2 Enrichment (FACE) experiments. The simulated global net biome productivity (NBP) is compared with the residual land sink (RLS) of the global carbon budget from Friedlingstein et al. [Nature Geoscience 3 (2010) 811] (FR10). We found that models produce a higher GPP (133 � 15 Pg C yr � 1 ) than JU11 (118 � 6P g Cy r � 1 ). In response to rising atmospheric CO2 concentration, modeled
619 citations
Cites background from "Responses of ecosystem carbon cycle..."
...In addition, at the regional scale, the correlation of interannual NBP among different models is higher in the tropical regions than that in nontropical regions (Fig....
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TL;DR: In a 26-year soil warming experiment in a mid-latitude hardwood forest, changes in soil carbon cycling are documented to investigate the potential consequences for the climate system and support projections of a long-term, self-reinforcing carbon feedback from mid- latitude forests to theClimate system as the world warms.
Abstract: In a 26-year soil warming experiment in a mid-latitude hardwood forest, we documented changes in soil carbon cycling to investigate the potential consequences for the climate system. We found that soil warming results in a four-phase pattern of soil organic matter decay and carbon dioxide fluxes to the atmosphere, with phases of substantial soil carbon loss alternating with phases of no detectable loss. Several factors combine to affect the timing, magnitude, and thermal acclimation of soil carbon loss. These include depletion of microbially accessible carbon pools, reductions in microbial biomass, a shift in microbial carbon use efficiency, and changes in microbial community composition. Our results support projections of a long-term, self-reinforcing carbon feedback from mid-latitude forests to the climate system as the world warms.
483 citations
TL;DR: In this paper, the uncertainties and modelling challenges involved in projecting soil responses to global warming are considered, and a review of the modelling challenges and uncertainties involved in predicting soil responses is presented.
Abstract: Climate change may accelerate decomposition of soil carbon leading to a reinforcing cycle of further warming and soil carbon loss. This Review considers the uncertainties and modelling challenges involved in projecting soil responses to warming.
458 citations
TL;DR: In this article, a comprehensive set of evidence of how hydrolase and oxidase activities respond to N fertilization in various ecosystems was provided. But the relationship between response ratios (RRs) of EEA and SOC, soil N (TN), and soil microbial biomass carbon (MBC) were explored when they were reported simultaneously.
Abstract: Nitrogen (N) fertilization affects the rate of soil organic carbon (SOC) decomposition by regulating extracellular enzyme activities (EEA). Extracellular enzymes have not been represented in global biogeochemical models. Understanding the relationships among EEA and SOC, soil N (TN), and soil microbial biomass carbon (MBC) under N fertilization would enable modeling of the influence of EEA on SOC decomposition. Based on 65 published studies, we synthesized the activities of α-1,4-glucosidase (AG), β-1,4-glucosidase (BG), β- d -cellobiosidase (CBH), β-1,4-xylosidase (BX), β-1,4-N-acetyl-glucosaminidase (NAG), leucine amino peptidase (LAP), urease (UREA), acid phosphatase (AP), phenol oxidase (PHO), and peroxidase (PEO) in response to N fertilization. The proxy variables for hydrolytic C acquisition enzymes (C-acq), N acquisition (N-acq), and oxidative decomposition (OX) were calculated as the sum of AG, BG, CBH and BX; AG and LAP; PHO and PEO, respectively. The relationships between response ratios (RRs) of EEA and SOC, TN, or MBC were explored when they were reported simultaneously. Results showed that N fertilization significantly increased CBH, C-acq, AP, BX, BG, AG, and UREA activities by 6.4, 9.1, 10.6, 11.0, 11.2, 12.0, and 18.6%, but decreased PEO, OX and PHO by 6.1, 7.9 and 11.1%, respectively. N fertilization enhanced SOC and TN by 7.6% and 15.3%, respectively, but inhibited MBC by 9.5%. Significant positive correlations were found only between the RRs of C-acq and MBC, suggesting that changes in combined hydrolase activities might act as a proxy for MBC under N fertilization. In contrast with other variables, the RRs of AP, MBC, and TN showed unidirectional trends under different edaphic, environmental, and physiological conditions. Our results provide the first comprehensive set of evidence of how hydrolase and oxidase activities respond to N fertilization in various ecosystems. Future large-scale model projections could incorporate the observed relationship between hydrolases and microbial biomass as a proxy for C acquisition under global N enrichment scenarios in different ecosystems.
430 citations
References
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TL;DR: This work has suggested that several environmental constraints obscure the intrinsic temperature sensitivity of substrate decomposition, causing lower observed ‘apparent’ temperature sensitivity, and these constraints may, themselves, be sensitive to climate.
Abstract: Significantly more carbon is stored in the world's soils--including peatlands, wetlands and permafrost--than is present in the atmosphere. Disagreement exists, however, regarding the effects of climate change on global soil carbon stocks. If carbon stored belowground is transferred to the atmosphere by a warming-induced acceleration of its decomposition, a positive feedback to climate change would occur. Conversely, if increases of plant-derived carbon inputs to soils exceed increases in decomposition, the feedback would be negative. Despite much research, a consensus has not yet emerged on the temperature sensitivity of soil carbon decomposition. Unravelling the feedback effect is particularly difficult, because the diverse soil organic compounds exhibit a wide range of kinetic properties, which determine the intrinsic temperature sensitivity of their decomposition. Moreover, several environmental constraints obscure the intrinsic temperature sensitivity of substrate decomposition, causing lower observed 'apparent' temperature sensitivity, and these constraints may, themselves, be sensitive to climate.
5,367 citations
"Responses of ecosystem carbon cycle..." refers background in this paper
...However, it is still uncertain as to whether or not plant C accumulation leads to a positive or negative feedback to climate warming (Cao and Wood- ward 1998, Cox et al. 2000, Melillo et al. 2002, Davidson and Janssens 2006, Smith and Fang 2010)....
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TL;DR: A consistent temperature-related shift is revealed in species ranging from molluscs to mammals and from grasses to trees, suggesting that a significant impact of global warming is already discernible in animal and plant populations.
Abstract: Over the past 100 years, the global average temperature has increased by approximately 0.6 °C and is projected to continue to rise at a rapid rate1. Although species have responded to climatic changes throughout their evolutionary history2, a primary concern for wild species and their ecosystems is this rapid rate of change3. We gathered information on species and global warming from 143 studies for our meta-analyses. These analyses reveal a consistent temperature-related shift, or ‘fingerprint’, in species ranging from molluscs to mammals and from grasses to trees. Indeed, more than 80% of the species that show changes are shifting in the direction expected on the basis of known physiological constraints of species. Consequently, the balance of evidence from these studies strongly suggests that a significant impact of global warming is already discernible in animal and plant populations. The synergism of rapid temperature rise and other stresses, in particular habitat destruction, could easily disrupt the connectedness among species and lead to a reformulation of species communities, reflecting differential changes in species, and to numerous extirpations and possibly extinctions.
4,532 citations
"Responses of ecosystem carbon cycle..." refers background in this paper
...The results indicate that the responses of plant C pool from aboveground part to experimental warming were more sensitive at higher latitudes at which the annual temperature is lower (Root et al. 2003), but the pattern was not applicable to belowground C dynamics....
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Book•
01 Sep 1979
3,864 citations
"Responses of ecosystem carbon cycle..." refers background in this paper
...It is well known that decomposition processes are governed by physical environments, substrate quality and quantity, and composition and activities of the decomposers (Swift et al. 1979)....
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TL;DR: Results from a fully coupled, three-dimensional carbon–climate model are presented, indicating that carbon-cycle feedbacks could significantly accelerate climate change over the twenty-first century.
Abstract: The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to significant changes in climate. About half of the current emissions are being absorbed by the ocean and by land ecosystems, but this absorption is sensitive to climate as well as to atmospheric carbon dioxide concentrations, creating a feedback loop. General circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and CO2 concentrations from simple carbon-cycle models that do not include climate change. Here we present results from a fully coupled, three-dimensional carbon–climate model, indicating that carbon-cycle feedbacks could significantly accelerate climate change over the twenty-first century. We find that under a 'business as usual' scenario, the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr-1 is balanced by the terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in uncoupled carbon models, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.
3,816 citations
"Responses of ecosystem carbon cycle..." refers background in this paper
...However, it is still uncertain as to whether or not plant C accumulation leads to a positive or negative feedback to climate warming (Cao and Wood- ward 1998, Cox et al. 2000, Melillo et al. 2002, Davidson and Janssens 2006, Smith and Fang 2010)....
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...Most global models have predicted a C loss from SOM and/or a decrease in NPP, resulting in a positive feedback to climate warming (Cao and Woodward 1998, Cox et al. 2000, Friedlingstein et al. 2006)....
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TL;DR: An empirical equation is presented which yields an unbiased estimator of respiration rates over a wide range of temperatures and provides representative estimates of the seasonal cycle of net ecosystem productivity and its effects on atmospheric CO 2.
Abstract: From previously published measurements of soil respiration rate (R) and temperature (T) the goodness of fit of various R vs T relationships was evaluated. Exponential (Q 10 ) and conventional Arrhenius relationships between T and R cannot provide an unbiased estimate of respiration rate. Nor is a simple linear relationship appropriate. The relationship between R and T can, however, be accurately represented by an Arrhenius type equation where the effective activation energy for respiration varies inversely with temperature. An empirical equation is presented which yields an unbiased estimator of respiration rates over a wide range of temperatures. When combined with seasonal estimates of Gross Primary Productivity (GPP) the empirical relationship derived provides representative estimates of the seasonal cycle of net ecosystem productivity and its effects on atmospheric CO 2 (...)
3,615 citations
"Responses of ecosystem carbon cycle..." refers methods in this paper
...…studies by various approaches such as meta-analysis (Rustad et al. 2001, Wu et al. 2011), synthetic analyses along MAT (or latitude) gradient (Lloyd and Taylor 1994), mesocosm experiments (Lin et al. 1999), and laboratory incubation (Flanagan and Veum 1974) suggest that experimental warming…...
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