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1.
Responses of terrestrial ecosystems to a world undergoing a change in atmospheric CO2 concentration presents a formidable challenge to terrestrial ecosystem scientists. Strong relationships among climate, atmosphere, soils and biota at many different temporal and spatial scales make the understanding and prediction of changes in net ecosystem production (NEP) at a global scale difficult. Global C cycle models have implicitly attempted to account for some of this complexity by adapting lower pool sizes and smaller flux rates representing large regions and long temporal averages than values appropriate for a small area. However, it is becoming increasingly evident that terrestrial ecosystems may be experiencing a strong transient forcing as a result of increasing levels of atmospheric CO2 that will require a finer temporal and spatial representation of terrestrial systems than the parameters for current global C cycle models allow. To adequately represent terrestrial systems in the global C cycle it is necessary to explicitly model the response of terrestrial systems to primary environmental factors. While considerable progress has been made experimentally and conceptually in aspects of photosynthetic responses, and gross and net primary production, the application of this understanding to NEP at individual sites is not well developed. This is an essential step in determining effects of plant physiological responses on the global C cycle. We use a forest stand succession model to explore the effects of several possible plant responses to elevated atmospheric CO2 concentration. These simulations show that ecosystem C storage can be increased by increases in individual tree growth rate, reduced transpiration, or increases in fine root production commensurate with experimental observations.  相似文献   

2.
The mechanisms that regulate the concentration of carbon dioxide in the atmosphere, the carbon cycle, is an integral part of the analysis of the greenhouse issue. The present understanding of the carbon cycle is inadequate to the purpose of assessing the relationship between future anthropogenic emissions and concentrations of atmospheric CO2. The most important problem is that natural science cannot presently explain the relationship between present and past anthropogenetic emissions and concentrations. Sinks for CO2 are inadequate to explain present and past dispositions of emissions. This deficiency in scientific understanding leads to uncertainty in the analysis of potential future emissions and atmospheric CO2 accumulation, and to uncertainty in the specification of other policy analysis instruments such as global warming potential coefficients.  相似文献   

3.
Interactions between N deposition and the fluxes between atmosphere and forest ecosystems of the greenhouse gases CO2, CH4 and N2O are examined. It is argued that forest productivity has increased due to increased N deposition since the industrial revolution in areas where N has been limiting to forest production. It is shown that most boreal and large parts of temperate forests growing on mineral soils are N limited still today. The increased above ground production due to improved N availability seems to result in an equal sized build-up of the C pool of at least boreal forest soils, in the first place in the humus layer. This is explained by an increased litter production of needles and roots and a decreased decomposition rate in an N rich environment. N deposition thus contributes to reduce the atmospheric levels of CO2. In areas where N is still limiting forest growth, a decreased N deposition, thus, logically, would result in decreased forest productivity and act as a source of increased CO2 levels to the atmosphere. Increased N deposition results in decreased CH4 oxidation of forest mineral soils and thus, acts to increase the greenhouse effect. However, this mechanism expressed as greenhouse contribution probably is small in relation to the reduction caused by increased CO2 fixation. From most forest mineral soils there seem to be small rates of N2O formation independently of deposition rates.  相似文献   

4.
Natural CO2 sinks in terrestrial and marine environments are important components of the global carbon cycle, yet the sign and magnitudes of key fluxes among them are unknown. The results of the Palmas Del Mar Workshop — Natural Sinks of CO2 presented in this special issue and its companion hardbound volume of Water, Air, & Soil Pollution, provide a synthesis of current research on the carbon cycle, CO2 sinks and associated processes and fluxes, and critical research needs to assess the potential role of forest and land-use management in carbon sequestration. The papers in this volume present data, observations, and model simulations that demonstrate: 1) the existence of natural CO2 sinks that could mitigate a significant amount of CO2 emissions from fossilfuel combustion; 2) probable, human-caused imbalances in C exchanges among vegetation, soils, and the atmosphere; 3) enhanced C storage in vegetation in response to excess atmospheric CO2; 4) strong interactions among carbon, nutrient and hydrological cycles; and 5) an excess of carbon production over consumption in several, large managed forests. Although it appears unlikely that the search for the “missing” C sink required to balance the C budget will end in the open ocean, new estimates of C storage in mangrove wood and peat, suggest that coastal ecosystems have the capacity to store significant amounts of carbon in vegetation and sediments. Convincing analyses are also presented indicating the technical and economical feasibility of managing existing lands to sequester additional carbon. Long-term field studies of CO2 fertilization effects and carbon cycling by plants and soils in geographically important systems, native forests, and coastal ecosystems will go a long way toward meeting the research needs identified at the workshop.  相似文献   

5.
General concern about climate change has led to growing interest in the responses of terrestrial ecosystems to elevated concentrations of CO2 in the atmosphere. Experimentation during the last two to three decades using a large variety of approaches has provided sufficient information to conclude that enrichment of atmospheric CO2 may have severe impact on terrestrial ecosystems. This impact is mainly due to the changes in the organic C dynamics as a result of the effects of elevated CO2 on the primary source of organic C in soil, i.e., plant photosynthesis. As the majority of life in soil is heterotrophic and dependent on the input of plant-derived organic C, the activity and functioning of soil organisms will greatly be influenced by changes in the atmospheric CO2 concentration. In this review, we examine the current state of the art with respect to effects of elevated atmospheric CO2 on soil microbial communities, with a focus on microbial community structure. On the basis of the existing information, we conclude that the main effects of elevated atmospheric CO2 on soil microbiota occur via plant metabolism and root secretion, especially in C3 plants, thereby directly affecting the mycorrhizal, bacterial, and fungal communities in the close vicinity of the root. There is little or no direct effect on the microbial community of the bulk soil. In particular, we have explored the impact of these changes on rhizosphere interactions and ecosystem processes, including food web interactions.  相似文献   

6.
The accelerated greenhouse effect and the degradation of land resources by water and wind erosion are two major, yet interrelated global environmental challenges. Accelerated decomposition of soil organic carbon (SOC) in cultivated soils results in decline in SOC stocks over time and also contributes to increased levels of CO2 in the atmosphere. Off‐site transport of SOC in runoff waters during erosional events also contributes to SOC depletion, but there is a paucity of data in the literature documenting erosional SOC losses and the fate of eroded SOC. In this paper, we present a mass balance approach to compute CO2 evolved from mineralization of SOC during transport and deposition of eroded soils. Erosion‐induced CO2 emission rates ranging between 6 and 52 g C m−2 yr−1 were computed using data on SOC stocks and dynamics from a series of long‐term experiments conducted across a range of ecological regions. For the cropland of the world, we estimated an annual flux of 0.37 Pg CO2‐C to the atmosphere due to water erosion. This flux is significant and suggests that water erosion must be taken into consideration when constructing global and regional C budgets. Through its contribution to atmospheric CO2 increase, water erosion can have a positive feedback on the accelerated greenhouse effect. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

7.
Land and water interface zones   总被引：1，自引：0，他引：1  
This paper reports analyses of C pools and fluxes in land-water interface zones completed at the International Workshop: Terrestrial Biospheric Carbon Fluxes; Quantification of Sinks and Sources of CO2 (Bad Harzburg, Germany, March 1–5, 1993). The objective was to determine the role of these zones as global sinks of atmospheric CO2 as part of a larger effort to quantify global C sinks and sources in the past (ca. 1850), the present, and the foreseeable future (ca. 2050). Assuming the world population doubles by the year 2050, storage of atmospheric C in reservoirs will also double, as will river loads of atmospheric C and nutrients. It is estimated that C sinks in temperate and boreal wetlands have decreased by about 50%, from 0.2 to 0.1 Gt C yr?1 since 1850. The total decrease for wetlands may be considerably larger when tropical wetlands are taken into account, however, the area and C density of tropical wetlands are not well known at this time. Changes in cultivation practices and improved sampling of methaneogenesis have caused estimates of CH4 emissions from ricelands to drop substantially from 150 to 60 Tg yr?1. Even with doubled N and P loads, rivers are unlikely to fertilize more than about 20% of the new primary production in the coastal ocean. The source of C for this new production may not be the atmosphere, however, because the coastal ocean exchanges large quantities of DIC with the open ocean. Until the C fluxes from air-sea exchange of CO2 and DIC are better quantified, the C-sink potential of the coastal ocean will remain a major uncertainty in the global C cycle. Analysis of model simulations of oceanic C uptake reconfirmed that the open ocean appears to take up about 2.0 Gt C yr?1 from the atmosphere and that model estimates are in better accord now, ±0.5 Gt C yr?1, than ever before. Land use management must consider the unique C sinks in coastal and alluvial wetlands in order to minimize the future negative impacts of agriculture and urban development. Long-term monitoring will be essential to prove the success, or failure, of management practices to sustain wetlands in the future. Relative to the other systems examined at the workshop, the C-sink capacity of the ocean (excluding estuaries) is not likely to be measurably affected in the foreseeable future by the management scenarios considered at the workshop.  相似文献   

8.
Most studies implicitly consider soil carbon dioxide (CO2) efflux as the instantaneous soil respiration and thereby neglect possible changes in the amount of CO2 stored in the soil pore‐space. We measured the CO2 concentration profile of a well‐aerated soil continuously to evaluate the dynamics of the stored CO2 and to analyse the influence of environmental factors. For 25% of the observation period, changes in the amount of stored CO2 accounted for more than 15% of the soil‐CO2 efflux. The following factors were identified to interfere with steady‐state CO2 storage: (i) the fluctuating groundwater table altered the volume of the vadose zone, causing viscous airflow in air‐filled soil pores, (ii) atmospheric turbulence caused pressure‐pumping at the soil–atmosphere interface and (iii) intense rain greatly reduced the diffusivity of the uppermost soil layer. The friction velocity above the canopy was strongly correlated with fluctuations in the differential pressure between soil air and atmosphere, but no static pressure gradient could be detected because of the permeable nature of the soil. Unexpected short‐term declines in the soil CO2 concentration were observed during intense rainfall events. These declines were explained by the intensified CO2 saturation deficit of the infiltrating rainwater caused by the carbonate chemistry of the soil solution.  相似文献   

9.
Similar to higher plants, microbial autotrophs possess photosynthetic systems that enable them to fix CO2. To measure the activity of microbial autotrophs in assimilating atmospheric CO2, five paddy soils were incubated with 14C-labeled CO2 for 45 days to determine the amount of 14C-labeled organic C being synthesized. The results showed that a significant amount of 14C-labeled CO2 incorporated into microbial biomass was soil specific, accounting for 0.37%–1.18% of soil organic carbon (14C-labeled organic C range: 81.6–156.9 mg C kg?1 of the soil after 45 days). Consequently, high amounts of C-labeled organic C were synthesized (the synthesis rates ranged from 86 to 166 mg C m?2 d?1). The amount of atmospheric 14CO2 incorporated into microbial biomass (14C-labeled microbial biomass) was significantly correlated with organic C components (14C-labeled organic C) in the soil (r = 0.80, p < 0.0001). Our results indicate that the microbial assimilation of atmospheric CO2 is an important process for the sequestration and cycling of terrestrial C. Our results showed that microbial assimilation of atmospheric CO2 has been underestimated by researchers globally, and that it should be accounted for in global terrestrial carbon cycle models.  相似文献   

10.
Soil processes and global change   总被引：43，自引：0，他引：43  
 Contributors to the Intergovernmental Panel on Climate Change (IPCC) generally agree that increases in the atmospheric concentration of greenhouse trace gases (i.e., CO2, CH4, N2O, O3) since preindustrial times, about the year 1750, have led to changes in the earth's climate. During the past 250 years the atmospheric concentrations of CO2, CH4, and N2O have increased by 30, 145, and 15%, respectively. A doubling of preindustrial CO2 concentrations by the end of the twenty-first century is expected to raise global mean surface temperature by about 2  °C and increase the frequency of severe weather events. These increases are attributed mainly to fossil fuel use, land-use change, and agriculture. Soils and climate changes are related by bidirectional interactions. Soil processes directly affect climatic changes through the production and consumption of CO2, CH4, and N2O and, indirectly, through the production and consumption of NH3, NOx, and CO. Although CO2 is primarily produced through fossil fuel combustion, land-use changes, conversion of forest and grasslands to agriculture, have contributed significantly to atmospheric increase of CO2. Changes in land use and management can also result in the net uptake, sequestration, of atmospheric CO2. CH4 and N2O are produced (30% and 70%, respectively) in the soil, and soil processes will likely regulate future changes in the atmospheric concentration of these gases. The soil-atmosphere exchange of CO2, CH4, and N2O are interrelated, and changes in one cycle can impart changes in the N cycle and resulting soil-atmosphere exchange of N2O. Conversely, N addition increases C sequestration. On the other hand, soil processes are influenced by climatic change through imposed changes in soil temperature, soil water, and nutrient competition. Increasing concentrations of atmospheric CO2 alters plant response to environmental parameters and frequently results in increased efficiency in use of N and water. In annual crops increased CO2 generally leads to increased crop productivity. In natural systems, the long-term impact of increased CO2 on ecosystem sustainability is not known. These changes may also result in altered CO2, CH4, and N2O exchange with the soil. Because of large temporal and spatial variability in the soil-atmosphere exchange of trace gases, the measurement of the absolute amount and prediction of the changes of these fluxes, as they are impacted by global change on regional and global scales, is still difficult. In recent years, however, much progress has been made in decreasing the uncertainty of field scale flux measurements, and efforts are being directed to large scale field and modeling programs. This paper briefly relates soil process and issues akin to the soil-atmosphere exchange of CO2, CH4, and N2O. The impact of climate change, particularly increasing atmospheric CO2 concentrations, on soil processes is also briefly discussed. Received: 1 December 1997  相似文献   

11.
A 3-D global ocean model used previously to determine natural oceanic uptake of anthropogenic CO2 is used here to evaluate another proposed strategy for mitigation of rising atmospheric CO2. As a reference, this study bases itself on previous efforts with the same model to evaluate the potential of Fe fertilization as a means to enhance oceanic CO2 uptake. From that base, we test the feasibility of slowing the rise in atmospheric CO2 by enhancing growth of seaweed, a proposal resurrected from previous efforts considering it as a means to grow marine biomass as fuel for energy production. To determine its maximum potential, logistical and financial constraints are ignored. An enhanced growth of 1 GT C yr?1 is prescribed to be evenly distributed over a large ocean area such as the equatorial band from 18°S to 18°N and the northern and southern subtropics from 18° to 49° latitude. Results from these simulations clearly demonstrate that the CO2 invasion from the atmosphere is substantially less than C removed from the surface via enhanced growth. When enhanced growth is supported only by naturally available nutrients, the enhancement to the air to sea CO2 flux averages 0.2 GT C yr?1 for the first 100 yr. When nutrients are supplied artificially to support the enhanced growth, the mean enhanced air to sea flux is more (for the first 100 yr it averages 0.72 GT C yr?1 when all enhanced growth is harvested but only 0.44 GT C yr?1 without harvesting); however, generating enhanced marine growth at 1 GT C yr?1 requires an unreasonably large supply of nutrient—close to the world's current rate of fertilizer production for P and substantially more than that for N. Less nutrient is needed if the enhanced algal growth is not harvested and thus respired, but respiration increases demand for oxygen so that significant anoxia develops. We conclude that growth of macroalgae is an inefficient mechanism for sequestering anthropogenic CO2 and that the use of macroalgae as an additional fuel source will actually result in a net transfer of CO2 from ocean to atmosphere; however, there would be a reduction in the atmospheric CO2 increase rate if macroalgae were used as a partial replacement for fossil fuel.  相似文献   

12.
Both acid deposition and changes in the global atmosphere and climate affect terrestrial and aquatic ecosystems. In the atmosphere sulphate aerosols tend to increase haze, altering the global radiation balance. Increased nitrogen deposition to N-limited systems such as boreal forests results in increased growth and increased sequestration of atmospheric CO2, slowing the increase in CO2 levels in the atmosphere. Future reduction in S and N emissions may result in a trade-off -- better with respect to some effects of acid deposition and greenhouse warming, but worse with respect to others. Global warming may cause the incidence and severity of drought to increase. Mineralisation of N and oxidation of organic S compounds release pulses of SO4, acid and Al to surface waters. Effects in lakes may include reduced deep water refugia for cold stenotherms, lower nutrient concentrations, and greater penetration of harmful UV radiation. Longer water renewal times cause declines in SO4 and NO3, due to increased in situ removal, but increases in base cations. The net result is increased internal alkalinity production. In areas characterised by cold winters, global warming may result in a major shift in hydrologic cycle, with snowmelt episodes occurring during the winter rather than the typical pattern of accumulation in the winter and melting in the spring. Increased storm frequency predicted for the future will cause increased frequency and severity of sea salt episodes in coastal regions. Predicting the interactions of regional and global environmental factors in the coming decades poses new challenges to scientists, managers and policy-makers.  相似文献   

13.
An analysis is undertaken to examine the potential impacts of a global climate change on patterns of potential terrestrial C storage and resulting fluxes between terrestrial and atmospheric pools. A bioclimatic model relating the current distribution of vegetation to global climate patterns is used to examine the potential impacts of a global climate change on the global distribution of vegetation. Climate change scenarios are based on the predictions of two general circulation model equilibrium simulations for a 2XCO2 atmosphere. Current estimates of C reserves in the vegetation types and associated soils are then used to calculate changes in potential terrestrial C storage under the two climate change scenarios. Results suggest a potential negative feedback to increasing atmospheric concentrations of CO2, with the potential for terrestrial C storage increasing under both scenarios. These results represent an equilibrium analysis, assuming the vegetation and soils have tracked the spatial changes in climate patterns. An approach for providing an estimate of the transient response between the two equilibria (i.e., current and 2XCO2 climates) is presented. The spatial transitions in vegetation predicted by the equilibrium analyses are classified as to the processes controlling the transition (eg., succession, dieback, species immigration). Estimates of the transfer rates related to these processes are then used to estimate the temporal dynamics of the vegetation/soils change and the associated C pools. Results suggest that although the equilibrium analyses show an increased potential for C storage under the climate change, in the transient case the terrestrial surface acts as a source of CO2 over the first 50 to 100 yrs following climate change.  相似文献   

14.
 Determination of the C balance is of considerable importance when forecasting climate and environmental changes. Soil respiration and biological productivity of ecosystems (net primary production; NPP) are the basic components of the terrestrial C cycle. In this study, a previously made assessment of the annual CO2 flux from Russian soils was improved upon. CO2 emissions from Russian soils during the growing period were shown to represent, on average, 53–82% of the annual CO2 flux from Russian soils. The total annual CO2 flux from Russian soils was estimated at 4.50 Gt C (C source). The NPP of Russian ecosystems was estimated at 4.81 Gt C year–1 (C sink). Our calculations showed values of CO2 emissions and the C sink to be very close. This shows that, in general, terrestrial ecosystems are under steady state. Received: 1 December 1997  相似文献   

15.
Soil carbon dioxide (CO2) efflux is an important component of the carbon (C) cycle but the biological and physical processes involved in soil CO2 production and transport are not fully understood. To improve our knowledge, we present a new approach to measure simultaneously soil CO2 concentrations and efflux, and their respective isotopic signatures (δ13C‐CO2). To quantify soil air 13CO2 and 12CO2 concentrations, we adapted a method based on CO2 diffusion from soil pores into tubes with a highly gas‐permeable membrane wall. These tubes were placed horizontally at different depths in the soil. Air was sampled automatically from the tubes and injected through a diluting system into a tuneable diode laser absorption spectrometer. The CO2 and δ13C‐CO2 vertical profiles were thus obtained at hourly intervals. Our tests demonstrated the absence of fractionation in the membrane tubes for δ13C‐CO2. Subsequently, we set up field experiments for two forest soils, which showed that natural soil CO2 concentrations and δ13C‐CO2 were not affected significantly by the measurement system. While δ13C‐CO2 in air‐filled pores below 5 cm was constant over 3 days, we observed large diurnal variations in δ13C‐CO2 efflux. However, the average difference between the two measurements was close to ?4.4‰, which supports steady‐state diffusion over this 3‐day period. This new method seems to be a very effective way to measure the δ13C‐CO2 profile of the soil atmosphere, and demonstrates that the fractionation that occurs during diffusion is the main transport process that affects the δ13C‐CO2 of the soil CO2 efflux on a daily timescale while advection may account for within‐day variations.  相似文献   

16.
Agroecosystems contain about 12% of the terrestrial soil C and play an important role in the global C cycle. We describe a project to evaluate the degree to which management practices can affect soil C in agroecosystems. The objectives of the project are to determine if agricultural systems can be managed to conserve and sequester C and thereby reduce the accumulation of CO2 in the atmosphere, and to provide reference datasets and methodologies for agricultural assessments.  相似文献   

17.
Knowledge of seasonal trends and controls of soil CO2 emissions to the atmosphere is important for simulating atmospheric CO2 concentrations and for understanding and predicting the global carbon cycle. This is particularly the case for high arctic soils subject to extreme fluctuating environmental conditions. Based on field measurements of soil CO2 efflux, temperature, water content, pore gas composition in soil and frozen cores as well as detailed temperature experiments performed in the laboratory, we evaluated seasonal controls of CO2 effluxes from a well-drained tundra heath site in NE-Greenland. During the growing season, near-surface temperatures correlated well with observed CO2 effluxes (r2>0.9). However, during intensive thawing of near-surface layers we observed up to 1.5-fold higher effluxes than expected due to temperature alone. These high rates were consistent with high CO2 concentrations in frozen soil (>10% CO2) and suggested a spring burst event during soil thawing and a corresponding trapping of produced CO2 during winter. Laboratory experiments revealed that microbial soil respiration continued down to a least −18 °C and that up to 80% of the produced CO2 was trapped in soil at temperatures between 0 and −9 °C. The trapping of CO2 in frozen soil was positively correlated with soil moisture (r2=0.85) and led to an abrupt change of the temperature sensitivity (Q10) observed for soil CO2 release at 0 °C with Q10 values below 0 °C being up to 100-fold higher than above 0 °C. The results of sub-zero CO2 production allowed us to predict the microbial soil respiration throughout the year and to evaluate to what extent burst events during thawing can be explained by the release of CO2 being produced and trapped during winter. Taking only the upper 20 cm of the soil into account, winter soil respiration accounted for about 40% of the annual soil respiration. At least 14% of the winter CO2 production was trapped during the winter 2000-2001 and observed to be released upon thawing. Thus, the site-specific winter soil respiration is an important part of the annual C cycle and CO2 trapping should be accounted for in future field and modelling studies of soil respiration dynamics in arctic ecosystems. In conclusion, we have discovered a soil moisture dependent uncoupling of CO2 production and release in frozen soils with important implications for future field studies of Arctic C cycling.  相似文献   

18.
Forest systems cover more than 4.1×109 ha of the Earth's land area. The future response and feedbacks of forest systems to atmospheric pollutants and projected climate change may be significant. Boreal, temperate and tropical forest systems play a prominent role in carbon (C), nitrogen (N) and sulfur (S) biogeochemical cycles at regional and global scales. The timing and magnitude of future changes in forest systems will depend on environmental factors such as a changing global climate, an accumulation of CO2 in the atmosphere, and increase global mineralization of nutrients such as N and S. The interactive effects of all these factors on the world's forest regions are complex and not intuitively obvious and are likely to differ among geographic regions. Although the potential effects of some atmospheric pollutants on forest systems have been observed or simulated, large uncertainty exists in our ability to project future forest distribution, composition and productivity under transient or nontransient global climate change scenarios. The potential to manage and adapt forests to future global environmental conditions varies widely among nations. Mitigation practices, such as liming or fertilization to ameliorate excess NOx or SOx or forest management to sequester CO2 are now being applied in selected nations worldwide.The U.S. Government's right to a non-exclusive, royalty free licence in and to any copyright is acknowledged.  相似文献   

19.
综述：土壤甲烷生成及其营养的研究进展   总被引：3，自引：0，他引：3  
Global warming,as a result of an increase in the mean temperature of the planet,might lead to catastrophic events for humanity.This temperature increase is mainly the result of an increase in the atmospheric greenhouse gases(GHG)concentration.Water vapor,carbon dioxide(CO2),methane(CH4)and nitrous oxide(N2O)are the most important GHG,and human activities,such as industry,livestock and agriculture,contribute to the production of these gases.Methane,at an atmospheric concentration of 1.7μmol mol-1currently,is responsible for 16%of the global warming due to its relatively high global warming potential.Soils play an important role in the CH4cycle as methanotrophy(oxidation of CH4)and methanogenesis(production of CH4)take place in them.Understanding methanogenesis and methanotrophy is essential to establish new agriculture techniques and industrial processes that contribute to a better balance of GHG.The current knowledge of methanogenesis and methanotrophy in soils,anaerobic CH4 oxidation and methanotrophy in extreme environments is also discussed.  相似文献   

20.
The net annual exchange of carbon between the atmosphere and terrestrial ecosystems is of prime importance in determining the concentration of CO2 ([CO2]) in the atmosphere and consequently future climate. Carbon loss occurs primarily through soil respiration; it is known that respiration is sensitive to the global changes in [CO2] and temperature, suggesting that the net carbon balance may change in the future. However, field manipulations of temperature and [CO2] alter many important environmental factors so it is unclear how much of the observed alterations in soil respiration is due to changes of microbial function itself instead of changes to the physical and chemical environment. Here we focus on resolving the importance of changes in the microbial community in response to warming and elevated [CO2] on carbon mineralisation, something not possible in field measurements. We took plant material and soil inocula from a long running experiment where native grassland had been exposed to both warming and elevated CO2 and constructed a reciprocal transplant experiment. We found that the rate of decomposition (heterotrophic respiration) was strongly determined by the origin of the microbial community. The combined warming + elevated CO2 treatment produced a soil community that gave respiration rates 30% higher when provided with shoot litter and 70% for root litter than elevated CO2 treatment alone, with the treatment source of the litter being unimportant. Warming, especially in the presence of elevated CO2, increased the size of the apparent labile carbon pool when either C3 or C4 litter was added. Thus, the metabolic activity of the soil community was affected by the combination of warming and elevated CO2 such that it had an increased ability to mineralise added organic matter, regardless of its source. Therefore, soil C efflux may be substantially increased in a warmer, high CO2 world. Current ecosystem models mostly drive heterotrophic respiration from plant litter quality, soil moisture and temperature but our findings suggest equal attention will need to be paid to capturing microbial processes if we are to accurately project the future C balance of terrestrial ecosystems and quantify the feedback effect on atmospheric concentrations of CO2.  相似文献   

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