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1.
Experimentation with dynamics of soil carbon pools as affected by elevated CO2 can better define the ability of terrestrial ecosystems to sequester global carbon. In the present study, 6 N HCl hydrolysis and stable-carbon isotopic analysis (δ13C) were used to investigate labile and recalcitrant soil carbon pools and the translocation among these pools of sorghum residues isotopically labeled in the 1998-1999 Arizona Maricopa free air CO2 enrichment (FACE) experiment, in which elevated CO2 (FACE: 560 μmol mol−1) and ambient CO2 (Control: 360 μmol mol−1) interact with water-adequate (wet) and water-deficient (dry) treatments. We found that on average 53% of the final soil organic carbon (SOC) in the FACE plot was in the recalcitrant carbon pool and 47% in the labile pool, whereas in the Control plot 46% and 54% of carbon were in recalcitrant and labile pools, respectively, indicating that elevated CO2 transferred more SOC into the slow-decay carbon pool. Also, isotopic mixing models revealed that increased new sorghum residue input to the recalcitrant pool mainly accounts for this change, especially for the upper soil horizon (0-30 cm) where new carbon in recalcitrant soil pools of FACE wet and dry treatments was 1.7 and 2.8 times as large as that in respective Control recalcitrant pools. Similarly, old C in the recalcitrant pool under elevated CO2 was higher than that under ambient CO2, indicating that elevated CO2 reduces the decay of the old C in recalcitrant pool. Mean residence time (MRT) of bulk soil carbon at the depth of 0-30 cm was significantly longer in FACE plot than Control plot by the averages of 12 and 13 yr under the dry and wet conditions, respectively. The MRT was positively correlated to the ratio of carbon content in the recalcitrant pool to total SOC and negatively correlated to the ratio of carbon content in the labile pool to total SOC. Influence of water alone on the bulk SOC or the labile and recalcitrant pools was not significant. However, water stress interacting with CO2 enhanced the shift of the carbon from labile pool to recalcitrant pool. Our results imply that terrestrial agroecosystems may play a critical role in sequestrating atmospheric CO2 and mitigating harmful CO2 under future atmospheric conditions.  相似文献   

2.
Soil respiration is an important component of terrestrial carbon cycling and can be influenced by many factors that vary spatially. This research aims to determine the extent and causes of spatial variation of soil respiration, and to quantify the importance of scale on measuring and modeling soil respiration within and among common forests of Northern Wisconsin. The potential sources of variation were examined at three scales: [1] variation among the litter, root, and bulk soil respiration components within individual 0.1 m measurement collars, [2] variation between individual soil respiration measurements within a site (<1 m to 10 m), and [3] variation on the landscape caused by topographic influence (100 m to 1000 m). Soil respiration was measured over a two-year period at 12 plots that included four forest types. Root exclusion collars were installed at a subset of the sites, and periodic removal of the litter layer allowed litter and bulk soil contributions to be estimated by subtraction. Soil respiration was also measured at fixed locations in six northern hardwood sites and two aspen sites to examine the stability of variation between individual measurements. These study sites were added to an existing data set where soil respiration was measured in a random, rotating, systematic clustering which allowed the examination of spatial variability from scales of <1 m to 100+ m. The combined data set for this area was also used to examine the influence of topography on soil respiration at scales of over 1000 m by using a temperature and moisture driven soil respiration model and a 4 km2 digital elevation model (DEM) to model soil moisture. Results indicate that, although variation of soil respiration and soil moisture is greatest at scales of 100 m or more, variation from locations 1 m or less can be large (standard deviation during summer period of 1.58 and 1.28 μmol CO2 m−2 s−1, respectively). At the smallest of scales, the individual contributions of the bulk soil, the roots, and the litter mat changed greatly throughout the season and between forest types, although the data were highly variable within any given site. For scales of 1-10 m, variation between individual measurements could be explained by positive relationships between forest floor mass, root mass, carbon and nitrogen pools, or root nitrogen concentration. Lastly, topography strongly influenced soil moisture and soil properties, and created spatial patterns of soil respiration which changed greatly during a drought event. Integrating soil fluxes over a 4 km2 region using an elevation dependent soil respiration model resulted in a drought induced reduction of peak summer flux rates by 37.5%, versus a 31.3% when only plot level data was used. The trends at these important scales may help explain some inter-annual and spatial variability of the net ecosystem exchange of carbon.  相似文献   

3.
Invasive earthworms can have significant impacts on C dynamics through their feeding, burrowing, and casting activities, including the protection of C in microaggregates and alteration of soil respiration. European earthworm invasion is known to affect soil micro- and mesofauna, but little is known about impacts of invasive earthworms on other soil macrofauna. Asian earthworms (Amynthas spp.) are increasingly being reported in the southern Appalachian Mountains in southeastern North America. This region is home to a diverse assemblage of native millipedes, many of which share niches with earthworm species. This situation indicates potential for earthworm-millipede competition in areas subject to Amynthas invasion.In a laboratory microcosm experiment, we used two 13C enriched food sources (red oak, Quercus rubra, and eastern hemlock, Tsuga canadensis) to assess food preferences of millipedes (Pseudopolydesmus erasus), to determine the effects of millipedes and earthworms (Amynthas corticis) on soil structure, and to ascertain the nature and extent of the interactions between earthworms and millipedes. Millipedes consumed both litter species and preferred red oak litter over eastern hemlock litter. Mortality and growth of millipedes were not affected by earthworm presence during the course of the experiment, but millipedes assimilated much less litter-derived C when earthworms were present.Fauna and litter treatments had significant effects on soil respiration. Millipedes alone reduced CO2 efflux from microcosms relative to no fauna controls, whereas earthworms alone and together with millipedes increased respiration, relative to the no fauna treatment. CO2 derived from fresh litter was repressed by the presence of macrofauna. The presence of red oak litter increased CO2 efflux considerably, compared to hemlock litter treatments.Millipedes, earthworms, and both together reduced particulate organic matter. Additionally, earthworms created significant shifts in soil aggregates from the 2000-250 and 250-53 μm fractions to the >2000 μm size class. Earthworm-induced soil aggregation was lessened in the 0-2 cm layer in the presence of millipedes. Earthworms translocated litter-derived C to soil throughout the microcosm.Our results suggest that invasion of ecosystems by A. corticis in the southern Appalachian Mountains is unlikely to be limited by litter species and these earthworms are likely to compete directly for food resources with native millipedes. Widespread invasion could cause a net loss of C due to increased respiration rates, but this may be offset by C protected in water-stable soil aggregates.  相似文献   

4.
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5.
Labile carbon is the fraction of soil organic carbon with most rapid turnover times and its oxidation drives the flux of CO2 between soils and atmosphere. Available chemical and physical fractionation methods for estimating soil labile organic carbon are indirect and lack a clear biological definition. We have modified the well-established Jenkinson and Powlson's fumigation-incubation technique to estimate soil labile organic carbon using a sequential fumigation-incubation procedure. We define soil labile organic carbon as the fraction of soil organic carbon degradable during microbial growth, assuming that labile organic carbon oxidizes according to a simple negative exponential model. We used five mineral soils and a forest Oa horizon to represent a wide range of organic carbon levels. Soil labile organic carbon varied from 0.8 mg/g in an Entisol to 17.3 mg/g in the Oa materials. Potential turnover time ranged from 24 days in an Alfisol to 102 days in an Ultisol. Soil labile organic carbon contributed from 4.8% in the Alfisol to 11.1% in the Ultisol to the total organic carbon. This new procedure is a relatively easy and simple method for obtaining indices for both the pool sizes and potential turnover rates of soil labile organic carbon and provides a new approach to studying soil organic carbon.  相似文献   

6.
In terrestrial ecosystems most carbon (C) occurs below-ground, making the activity of soil decomposer organisms critical to the global carbon cycle. Temperate grassland ecosystems, contain large, diverse and active soil meso- and macrofauna decomposer communities. Understanding the effects of climate change on their ecology offers a first step towards meaningful predictions of changes in soil organic carbon mineralisation.We examined the effects of soil warming on the abundance, diversity and ecology of temperate grassland soil fauna functional groups, ecosystem net CO2 flux and respiration and plant above- and below-ground productivity in a 2-year plant-soil mesocosm experiment. Low voltage heating cable mounted on a framework of stainless steel mesh provided a constant 3.5 °C difference between control and warmed mesocosm soils.Results showed that this temperature increment had little effect on soil respiration and above-ground plant biomass. There was, however, a significant effect on the soil fauna due to warmer conditions and increased root growth, with significant decreases in the numbers in the large oligochaete groups and Prostigmata mites and the re-distribution of enchytraeids to deeper soil layers. Functional groups exhibited individualistic responses to soil warming, with the total disappearance of epigeic species in the case of the ecosystem engineers and an increased diversity of fungivorous mites that, together, produced significant changes in the composition and trophic structure of the fauna community.The observed switch towards a fungal driven food web has important implications for the fate of soil organic carbon in temperate ecosystems subjected to sustained warming. Accordingly, soil biology needs to be properly incorporated in C models to make better predictions of the fate of SOC under warmer scenarios.  相似文献   

7.
Gap formation is suggested as an alternative forest management approach to avoid extreme changes in the N cycle of forest ecosystems caused by traditional management practises. The present study aimed to investigate the effect of gap formation on N availability in beech litter and mineral soil on sites, which experienced only little soil disturbance during tree harvest. N pools, litter decomposition, and N mineralization rates in mineral soil were studied in two gaps (17 and 30 m in diameter) in a 75-year-old managed European beech (Fagus sylvatica L.) forest in Denmark and related to soil temperature (5 cm depth) and soil moisture (15 cm depth). Investigations were carried out during the first 2 years after gap formation in measurement plots located along the north-south transect running through the centre of each gap and into the surrounding forest.An effect of gap size was found only for soil temperatures and litter mass loss: soil temperatures were significantly increased in the northern part of the large gap during the first year after gap formation, and litter mass loss was significantly higher in the smaller gap. All other parameters investigated revealed no effect of gap size. Nitrification, net mineralization, and soil N concentrations tended to be increased in the gaps. Cumulative rates of net mineralization were two fold higher in the gaps during the growing season (June-October), but a statistically significant increase was found only for soil NH4-N concentrations during this period. Forest floor parameters (C:N ratios, mass loss, N release) were not significantly modified during the first year after gap formation, neither were the total C content nor the C:N ratio in mineral soil at 0-10 cm depth.  相似文献   

8.
Soil animals are known to stimulate soil microbial activity and thereby to accelerate decomposition of soil organic matter. In this paper, we investigate potential limitations of soil animal effects on soil carbon flow by analysing how animal effects relate to the density of four major faunal groups. Specifically, we analyse the extent to which faunal effects are subject to biotic regulation or to mutual inhibition between groups under different levels of resource supply.In an extensive laboratory experiment, 96 microcosms established in three consecutive blocks were inoculated with nematodes, enchytraeids, microarthropods, and lumbricids. Each faunal group was inoculated in three densities, including combinations of groups. Introduced animal densities were within the natural range of densities in fallow soil. Bare agricultural soil and soil covered with maize litter were used as substrates. The microcosms were kept under constant conditions at 12 °C and 50% water holding capacity for 8 weeks. Soil CO2 evolution was measured daily by means of gas chromatography.Animal effects were on an average relatively stronger in bare soil (+95% CO2; R2=0.76) than in soil with litter (+14% CO2; R2=0.40), where organic matter decomposition was seven times more intense. Higher animal densities generally led to accelerated decomposition up to three times that of the controls. However, beyond a specific density, decomposition rates stopped increasing or even declined, depending on the faunal group. In addition, animal effects were limited by mutual inhibition between groups in bare soil where effects were strong, while stimulatory interactions were prominent in the litter treatments where effects were generally weak.We interpret the limitation of soil faunal effects on soil carbon flow in terms of incomplete habitat exploitation and biotic regulation. Under conditions of substrate homogeneity, such as in the bare soil treatments, animal effects were stronger, but they were limited by overexploitation. Under conditions of substrate heterogeneity, such as in the litter treatments, animal effects were limited by incomplete habitat utilisation. We assume that complementary habitat colonisation by different faunal groups in the litter treatments gave rise to positive diversity effects, but that these effects did not compensate for reduced overall habitat utilisation. We infer that a knowledge of faunal resource utilisation and of mutual inhibition of faunal groups can be exploited for ecological soil management towards stabilisation of soil organic matter.  相似文献   

9.
Elevated atmospheric CO2 tends to stimulate plant productivity, which could either stimulate or suppress the processing of soil carbon, thereby feeding back to atmospheric CO2 concentrations. We employed an acid-hydrolysis-incubation method and a net nitrogen-mineralization assay to assess stability of soil carbon pools and short-term nitrogen dynamics in a Florida scrub-oak ecosystem after six years of exposure to elevated CO2. We found that soil carbon concentration in the slow pool was 27% lower in elevated than ambient CO2 plots at 0-10 cm depth. The difference in carbon mass was equivalent to roughly one-third of the increase in plant biomass that occurred in the same experiment. These results concur with previous reports from this ecosystem that elevated CO2 stimulates microbial degradation of relatively stable soil organic carbon pools. Accordingly, elevated CO2 increased net N mineralization in the 10-30 cm depth, which may increase N availability, thereby allowing for continued stimulation of plant productivity by elevated CO2. Our findings suggest that soil texture and climate may explain the differential response of soil carbon among various long-term, field-based CO2 studies. Increased mineralization of stable soil organic carbon by a CO2-induced priming effect may diminish the terrestrial carbon sink globally.  相似文献   

10.
Woody plant invasion of grasslands is prevalent worldwide. In the Rio Grande Plains of Texas, subtropical thorn woodlands dominated by C3 trees/shrubs have been replacing C4 grasslands over the past 150 yr, resulting in increased soil organic carbon (SOC) storage and concomitant increases in soil total nitrogen (STN). To elucidate mechanisms of change in SOC and STN, we separated soil organic matter into specific size/density fractions and determined the concentration of C and N in these fractions. Soils were collected from remnant grasslands (Time 0) and woody plant stands (ages 10-130 yr). Rates of whole-soil C and N accrual in the upper 15 cm of the soil profile averaged 10-30 g C m−2 yr−1 and 1-3 g N m−2 yr−1, respectively, over the past 130 yr of woodland development. These rates of accumulation have increased soil C and N stocks in older wooded areas by 100-500% relative to remnant grasslands. Probable causes of these increased pool sizes include higher rates of organic matter production in wooded areas, greater inherent biochemical resistance of woody litter to decomposition, and protection of organic matter by stabilization within soil macro- and microaggregates. The mass proportions of the free light fraction (<1.0 g cm−3) and macroaggregate fraction (>250 μm) increased linearly with time following woody plant invasion of grassland. Conversely, the mass proportions of free microaggregate (53-250 μm) and free silt+clay (<53 μm) fractions decreased linearly with time after woody invasion, likely reflecting stabilization of these fractions within macroaggregate structures. Carbon and N concentrations increased in all soil fractions with time following woody invasion. Approximately half of the C and N accumulated in free particulate organic matter (POM) fractions, while the remainder accrued in stable macro- and microaggregate structures. Soil C/N ratios indicated that the organic C associated with POM and macroaggregates was of more recent origin (less decomposed) than C associated with the microaggregate and silt+clay fractions. Because grassland-to-woodland conversion has been geographically extensive in grassland ecosystems worldwide during the past century, changes in soil C and N storage and dynamics documented here could have significance for global cycles of those elements.  相似文献   

11.
Atypical soil carbon distribution across a tropical steepland forest catena   总被引：1，自引：0，他引：1  
Soil organic carbon (SOC) in a humid subtropical forest in Puerto Rico is higher at ridge locations compared to valleys, and therefore opposite to what is commonly observed in other forested hillslope catenas. To better understand the spatial distribution of SOC in this system, plots previously characterized by topographic position, vegetation type and stand age were related to soil depth and SOC. Additional factors were also investigated, including topographically-related differences in litter dynamics and soil chemistry. To investigate the influence of litter dynamics, the Century soil organic model was parameterized to simulate the effect of substituting valley species for ridge species. Soil chemical controls on C concentrations were investigated with multiple linear regression models using iron, aluminum and clay variables. Deeper soils were associated with indicators of higher landscape stability (older tabonuco stands established on ridges and slopes), while shallower soils persisted in more disturbed areas (younger non-tabonuco stands in valleys and on slopes). Soil depth alone accounted for 77% of the observed difference in the mean 0 to 60 cm SOC between ridge soils (deeper) and valley soils (shallower). The remaining differences in SOC were due to additional factors that lowered C concentrations at valley locations in the 0 to 10 cm pool. Model simulations showed a slight decrease in SOC when lower litter C:N was substituted for higher litter C:N, but the effects of different woody inputs on SOC were unclear. Multiple linear regression models with ammonium oxalate extractable iron and aluminum, dithionite–citrate-extractable iron and aluminum, and clay contents explained as much as 74% of the variation in C concentrations, and indicated that organo-mineral complexation may be more limited in poorly developed valley soils. Thus, topography both directly and indirectly affects SOC pools through a variety of inter-related processes that are often not quantified or captured in terrestrial carbon models.  相似文献   

12.
Forest soils contain the largest carbon stock of all terrestrial biomes and are probably the most important source of carbon dioxide (CO2) to atmosphere. Soil CO2 fluxes from 54 to 72-year-old monospecific stands in Rwanda were quantified from March 2006 to December 2007. The influences of soil temperature, soil water content, soil carbon (C) and nitrogen (N) stocks, soil pH, and stand characteristics on soil CO2 flux were investigated. The mean annual soil CO2 flux was highest under Eucalyptus saligna (3.92 μmol m−2 s−1) and lowest under Entandrophragma excelsum (3.13 μmol m−2 s−1). The seasonal variation in soil CO2 flux from all stands followed the same trend and was highest in rainy seasons and lowest in dry seasons. Soil CO2 flux was mainly correlated to soil water content (R2 = 0.36-0.77), stand age (R2 = 0.45), soil C stock (R2 = 0.33), basal area (R2 = 0.21), and soil temperature (R2 = 0.06-0.17). The results contribute to the understanding of factors that influence soil CO2 flux in monocultural plantations grown under the same microclimatic and soil conditions. The results can be used to construct models that predict soil CO2 emissions in the tropics.  相似文献   

13.
The aim of this field experiment was to quantify the contribution of soil fauna to plant litter decomposition in three forest sites differing in C/N ratio under natural conditions in Xishuangbanna, southwestern China. We conducted a survey of soil fauna communities, the forest floor litter and investigated mass loss of mixed tree species leaf litter for two years in a tropical secondary forest, an evergreen broad-leaf forest and a tropical rain forest. Exclusion treatments of different sized soil fauna from the leaf litter by using varying mesh size litter bags (2 mm and 0.15 mm) were also performed. Mass loss and C and N concentrations in litter bag leaf materials were determined at monthly intervals. We found that: (1) the three forests differed in floor litter biomass and nutrient contents but not in soil fauna richness and abundance; (2) litter mass loss and decomposition rate were slower when soil macrofauna and most of mesofauna were excluded; and (3) greatest soil fauna contribution to plant litter decomposition occurred in the rain forest, where leaf litter C/N ratio was also highest (41.5% contribution: 54.8 C/N ratio), in comparison to 8.69% in the broad-leaf forest and 19.52% in the secondary forest, both with low leaf litter C/N ratios (<32). Our results suggested that, soil fauna played a more pronounced role in the decomposition of mixed leaf litter in tropical rain forest, and significantly bigger effects from fauna were ascribed to the enhancement of N concentration and decrease of C concentration of the initially high C/N ratio litter in this forest site.  相似文献   

14.
A radiocarbon approach was used to investigate the roles of temperature and soil fauna activity in the turnover of ‘old’ non-labile carbon in a peatland ecosystem. We investigated the impacts of enchytraeids on carbon turnover in two different soil layers, with different incorporation of the ‘bomb’ peak, when incubated at two different temperatures. Results showed that, in agreement with previous studies, warmer temperatures promoted reproduction rates of enchytraeids, with the top layer supporting higher animal densities and biomass. With independence of the animal treatment, soil respiration in the top 5 cm was four times higher than in the deeper layer suggesting that decomposition was greater in the upper layer, with the response being greater at the highest temperature treatment. Furthermore, independent of temperature, the presence of enchytraeids in the top layer significantly enhanced the release of non-labile C as DOC. Similarly, at the bottom layer, ‘older’ C sources were mobilised in response to warming and a greater amount of pre-bomb carbon was released into the soil solution at 20 °C when the worms were present. A strong positive link between the ages of the C assimilated by the animals and released through mineralization suggests an important role of soil biology in the mobilisation of the older C pools in soils and should be taken into account in developing global C models to predict the response of soil C dynamics to climate change.  相似文献   

15.
Earthworms are important processors of soil organic matter (SOM) and nutrient turnover in terrestrial ecosystems. In agroecosystems, they are often seen as beneficial organisms to crop growth and are actively promoted by farmers and extension agents, yet their contribution to agroecosystem services is uncertain and depends largely on management. The Quesungual slash-and-mulch agroforestry system (QSMAS) of western Honduras has been proposed as a viable alternative to traditional slash-and-burn (SB) practices and has been shown to increase earthworm populations, yet the effect of earthworms on soil fertility and SOM in QSMAS is poorly understood. This study examined the role of Pontoscolex corethrurus in QSMAS by comparing their influence on aggregate-associated SOM and fertilizer dynamics with their effects under SB and secondary forest in a replicated field trial. Both the fertilized QSMAS and SB treatments had plots receiving additions of inorganic 15N and P, as well as plots with no inorganic N additions. Earthworm populations were manipulated in field microcosms at the beginning of the rainy season within each management treatment via additions of P. corethrurus or complete removal of existing earthworm populations. Microcosms were destructively sampled at harvest of Zea mays and soils were wet-sieved (using 53, 250 and 2000 μm mesh sizes) to isolate different aggregate size fractions, which were analyzed for total C, N and 15N. The effects of management system were smaller than expected, likely due to disturbance associated with the microcosm installation. Contrary to our hypothesis that earthworms would stabilize organic matter in soil aggregates, P. corethrurus decreased total soil C by 3% in the surface layer (0-15 cm), predominantly through a decrease in the C concentration of macroaggregates (>250 μm) and a corresponding depletion of C in coarse particulate organic matter occluded within macroaggregates. Earthworms also decreased bulk density by over 4%, but had no effect on aggregate size distribution. Within the two fertilized treatments, the QSMAS appeared to retain slightly more fertilizer derived N in smaller aggregate fractions (<250 μm) than did SB, while earthworms greatly reduced the recovery of fertilizer N (34% decrease) in both systems. Although management system did not appear to influence the impact of P. corethrurus on SOM or nutrient dynamics, we suggest the lack of differences may be due to artificially low inputs of fresh residue C to microcosms within all management treatments. Our findings highlight the potential for P. corethrurus to have deleterious impacts on soil C and fertilizer N dynamics, and emphasize the need to fully consider the activities of soil fauna when evaluating agroecosystem management options.  相似文献   

16.
Seasonal changes in multi-scale spatial variation in soil chemical properties, which may be controlled simultaneously by biotic and abiotic factors, have not been studied in tropical dry forests. We evaluated the spatial variation of physico-chemical soil properties, plant litter and terrain attributes at multiple scales in a tropical dry evergreen forest using multivariate geostatistics. Soil samples were collected at different depths using nested interval sampling during 1- and 10-m intervals in both the wet and dry seasons. We measured pH, exchangeable cations (Ex-K+ and Ex-Ca2+), acidity (Ex-H+ and Ex-Al3+), particle size (clay and sand contents), and forest floor mass (Oi and Oa). Pronounced spatial variation in pH was observed in surface soil (0-5 cm) but not in deeper soil (5-55 cm). Multi-scale spatial structures with short (20 m) and long (86 m) ranges were observed in the auto- and cross-variograms of soil, litter and slope gradient. Pronounced multi-scale structures were observed simultaneously in pH and Ex-Ca2+ both in the wet and dry seasons. Only a short-range structure was observed in Ex-K+ and Oa, whereas a long-range structure was pronounced in sand contents and slope gradients. Although the variograms had similar shapes between wet and dry seasons for almost all variables, the short-range structure of the cross-variogram between Oa with pH and base cations was more pronouncedly developed in the wet season than in the dry season. Scale-dependent correlation coefficients suggest that a small-scale spatial variation in pH was connected to heterogeneous litter accumulation via base-cation input, whereas long-range spatial variation was simultaneously linked to particle size and slope gradient. This multivariate geostatistical approach applied within a stand detected biotic and abiotic factors controlling spatial variation in soil properties at both short and long distances.  相似文献   

17.
Rice (Oryza sativa) was grown in sunlit, semi-closed growth chambers (4×3×2 m, L×W×H) at 650 μl l−1 CO2 (elevated CO2) to determine: (1) rice root-derived carbon (C) input into the soil under elevated CO2 in one growing season, and (2) the effect of the newly input C on decomposition of the more recalcitrant native soil organic C. The initial δ13C value of the experimental soil was −25.8‰, which was 6‰ less depleted in 13C than the plants grown under elevated CO2. Significant changes in δ13C of the soil organic C were detected after one growing season. The amount of new soil C input was estimated to be 0.9 t ha−1 (or 2.1%) at 30 kg N ha−1 and 1.8 t ha−1 (4.1%) at 90 kg N ha−1. Changes in soil δ13C suggested that the surface 5 cm of soil received more C input from plants than soils below. Laboratory incubation (25 °C) of soils from different horizons indicated that increased availability of the labile plant-derived C in the soil reduced decomposition of the native soil organic C. Provided the retardant effect of the new C on old soil organic C holds in the field in the longer-term, paddy soils will likely sequester more C from the atmosphere if more plant C enters the soil under elevated atmospheric CO2.  相似文献   

18.
The long-term storage of soil organic matter (SOM) in forest soils is still poorly understood. In this study, particle size fractionation in combination with accelerator mass spectroscopy (AMS) and solid state 13C nuclear magnetic resonance (NMR) spectroscopy was applied to investigate organic carbon (OC) stabilisation in Cambisol and Luvisol profiles under spruce (Picea abies) and beech (Fagus sylvatica L.) forests. In most samples, OC was preferentially associated with <2 μm fractions. Throughout soil profiles the contribution of OC in the clay fraction to the total OC increased from 27%-53% in A horizons to 44-86% in E, B and EB horizons. The 200-2000 μm fractions from all sites and all depths showed a percentage of modern C (pmC)>100. They were enriched in 14C owing to high inputs of recent material from leaves and roots. Clearly less active material was associated with <2 and 2-20 μm fractions. This demonstrated that the particle size fractionation procedure applied to our study was capable to isolate a young OC fraction in all samples. The pmC values were strongly decreasing with depth but the decrease was much more pronounced in the fine fractions. The <2 and 2-20 μm fractions of B, E and EB horizons revealed radiocarbon ages between 512 and 4745 years before present which indicated that the SOM in those horizons was little affected by the recent vegetation. The major components of labile and stable SOM pools in topsoils and subsoils were always O/N-alkyl C (28-53%) and alkyl C (14-48%) compounds. NMR spectra of bulk soils and particle size fractions indicated that high alkyl C and O/N-alkyl C proportions throughout the soil profile are typical of Cambisols and Luvisols which were not subjected to regular burning. A relation between radiocarbon age and chemical composition throughout soil profiles was not observed. This suggests that the long-term stabilisation of SOM is mainly controlled by the existence of various mechanisms of protection offered by the soil matrix and soil minerals but not by the chemical structure of SOM itself.  相似文献   

19.
Parallel incubation at different temperatures combined with 13CO2 efflux has been used to distinguish the temperature sensitivity of labile soil carbon (young soil carbon derived from newly-introduced vegetation) from that of resistant soil carbon (old, native vegetation-derived soil carbon). But we believe that this approach to assessing relative temperature sensitivities is confounded by differential rates of depletion of labile and resistant soil carbon at different temperatures. Here we employ a simple decomposition model to demonstrate potential pitfalls in interpreting 13CO2 efflux data that inevitably, and potentially erroneously, lead to the conclusion that decomposition of resistant soil carbon pools is more temperature sensitive than labile pools. We conclude by offering a new approach for interpreting these data that eliminates this potential bias.  相似文献   

20.
This work investigated the effects of land cover and land-use change (LUC) on the ability of a soil to store carbon (C) and reduce carbon dioxide (CO2) emissions, in a Mediterranean area. Using a paired-site approach, we estimated the effect of land-cover change on the C stock from 1972 to 2008 in a natural reserve (Grotta di Santa Ninfa) in western Sicily. We selected 15 paired sites representative of five LUCs. We studied the effect of land use on soil organic C (SOC) content in bulk soil and in different particle-size fractions (2000-1000 μm, 1000-500 μm, 500-250 μm, 250-63 μm, 63-25 μm, and < 25 μm). Laboratory incubation of the soil samples was conducted to measure CO2 evolution in bulk soil collected at two different depths from each paired site. We found that the conversion of natural vegetation to orchards (vineyards and olive groves) resulted in SOC decreases ranging from 27% to 50%. The conversion from vineyards to arable land led to a 9% decrease in SOC, whereas the opposite caused a 105% gain. When arable land was replaced by Eucalyptus afforestation, a 40% increase in SOC was observed. SOC decline occurred mainly in coarser soil fractions, whereas the finest fractions were not influenced by land use. We calculated an overall SOC reduction of 63% in the study area, corresponding to a 58 Mg ha− 1 SOC loss in less than 30 years. Our results indicate that land-use conversion, vegetation type, and management practices that control the biogeochemical and physical properties of soil could help reduce CO2 emissions and sequester SOC.  相似文献   

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