Storage and sequestration potential of topsoil organic carbon in China's paddy soils

Carbon (C) storage and sequestration in agricultural soils is considered to be an important issue in the study of terrestrial C cycling and global climatic change. The baseline C stock and the C sequestration potential are among the criteria for a region or a state to adopt strategies or policies in response to commitment to the Kyoto Protocol. Paddy soils represent a large portion of global cropland. However, little information on the potential of C sequestration and storage is available for such soils. In this paper, an estimation of the topsoil soil organic carbon (SOC) pool and the sequestration potential of paddy soils in China was made by using the data from the 2nd State Soil Survey carried out during 1979–1982 and from the nationwide arable soil monitoring system established since then. Results showed that the SOC density ranged from 12 to 226 t C ha^?1 with an area‐weighted mean density of 44 t C ha^?1, which is comparable to that of the US grasslands and is higher than that of the cultivated dryland soils in China and the US. The estimated total topsoil SOC pool is 1.3 Pg, with 0.85 Pg from the upper plow layer and 0.45 Pg from the plowpan layer. This pool size is ～2% of China's total storage in the top 1 m of the soil profiles and ～4% of the total topsoil pool, while the area percentage of paddy soil is 3.4% of the total land. The C pool in paddy soils was found predominantly in southeast China geographically and in the subgroups of Fe‐accumulating and Fe‐leaching paddy soils pedogenetically. In comparison with dryland cultivation, irrigation‐based rice cultivation in China has induced significant enrichment of SOC storage (0.3 Pg) in paddy soils. The induced total C sequestration equals half of China's total annual CO₂ emission in the 1990s. Estimates using different SOC sequestration scenarios show that the paddy soils of China have an easily attainable SOC sequestration potential of 0.7 Pg under present conditions and may ultimately sequester 3.0 Pg. Soil monitoring data showed that the current C sequestration rate is 12 Tg yr^?1. The total C sequestration potential and the current sequestration rate of the paddy soils are over 30%, while the area of the paddy soils is 26% that of China's total croplands. Therefore, practicing sustainable agriculture is urgently needed for enhancing SOC storage to realize the ultimate SOC sequestration of rice‐based agriculture of China, as the current C sequestration rate is significantly lower than the potential rate.     

Uncertainty analysis of soil organic carbon stock change in Canadian cropland from 1991 to 2001

National estimates of changes in the amount of soil organic carbon (SOC) in cropland requires an assessment of uncertainty for accounting and reporting under the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol. Canada has data sets on SOC stocks in croplands, historical changes in SOC levels due to management practices, and historical changes in the area of land devoted to certain soil management practices. We conducted an analysis of uncertainty of the change in SOC levels due to management practices in Canada from 1991 to 2001 using Monte Carlo analysis and a simple model. Probability distribution functions were determined for each of the inputs of the model, enabling us to assess the uncertainty for the output. The storage rate of SOC in cropland soils of Canada for the 10‐year period ranged from 3.2 to 8.3 Mt C yr^?1 at 95% confidence, with a mean of 5.7 Mt C yr^?1. Approximately 67% (about 3.8 Mt C yr^?1) of the increase in SOC storage in Canada occurred in Saskatchewan where the cropland area under no‐till increased from 10% to 35%, and the area of summer‐fallow declined from 43% to 20% during the study period. The large uncertainty in the effect of no‐till on SOC stock changes in the Gray‐Brown Luvisols of Ontario contributed most to the variance in the model output. If trends in agricultural management continue for the next 10‐year census period, the estimated SOC storage would comprise between 7% and 19% of the gap required to achieve the 6% reduction in 1990 greenhouse gas emission levels for Canada under the Kyoto Protocol.     

农田土壤有机碳固定潜力研究进展

土壤有机碳的贮存和损失的研究是目前国际上前沿研究领域之一。研究农田土壤有机碳固定过程 ,对于了解农业生产过程和生态过程的关系具有十分重要的意义。在农田土壤中 ,发生变化的有机碳主要是年轻或轻组有机碳 ,而且土壤有机碳的损失或固定都是在土壤表层和有限的时间内发生 ,且数量巨大。传统的耕作体系是造成土壤有机碳损失的主要原因。为了增加农田土壤有机碳的保有量 ,农业管理措施应该从增加有机碳的输入量 (如草田轮作、保留残茬以及施用肥料等 )和减少土壤有机碳的矿化 (少、免耕等 )两方面入手     

四川森林土壤有机碳储量的空间分布特征

利用森林土壤实测数据与GIS相结合的研究方法估算了四川森林土壤有机碳密度和碳储量,研究了四川森林土壤有机碳密度的空间分布特征.四川森林土壤有机碳储量为(2394.26 ±514.15) TgC,平均碳密度为190.45 Mg·hm-2;四川不同森林类型土壤有机碳储量和碳密度差异较大,分别介于(5.05±0.37)～(1101.74±205.40) TgC、(102.69±21.09)～(264.41±49.24) Mg·hm-2之间,其有机碳含量、碳密度和碳储量都随土层厚度的增加而降低.四川森林土壤有机碳密度空间分布特征明显,总体上表现出随纬度、海拔高度的增加而增加,随经度的增加而减小.从森林土壤生态系统水平监测森林土壤有机碳储量有助于提高其估算精度.     

Stocks and losses of soil organic carbon from Chinese vegetated coastal habitats

Global vegetated coastal habitats (VCHs) represent a large sink for organic carbon (OC) stored within their soils. The regional patterns and causes of spatial variation, however, remain uncertain. The sparsity and regional bias of studies on soil OC stocks from Chinese VCHs have limited the reliable estimation of their capacity as regional and global OC sinks. Here, we use field and published data from 262 sampled soil cores and 181 surface soils to report estimates of soil OC stocks, burial rates and losses of VCHs in China. We find that Chinese mangrove, salt marsh and seagrass habitats have relatively low OC stocks, storing 6.3 ± 0.6, 7.5 ± 0.6, and 1.6 ± 0.6 Tg C (±95% confidence interval) in the top meter of the soil profile with burial rates of 44 ± 17, 159 ± 57, and 6 ± 45 Gg C/year, respectively. The variability in the soil OC stocks is linked to biogeographic factors but is mostly impacted by sedimentary processes and anthropic activities. All habitats have experienced significant losses, resulting in estimated emissions of 94.2–395.4 Tg CO₂e (carbon dioxide equivalent) over the past 70 years. Reversing this trend through conservation and restoration measures has, therefore, great potential in contributing to the mitigation of climate change while providing additional benefits. This assessment, on a national scale from highly sedimentary environments under intensive anthropogenic pressures, provides important insights into blue carbon sink mechanism and sequestration capacities, thus contributing to the synchronous progression of global blue carbon management.     

Effects of cropland reclamation on soil organic carbon in China's black soil region over the past 35 years

The long-term use of cropland and cropland reclamation from natural ecosystems led to soil degradation. This study investigated the effect of the long-term use of cropland and cropland reclamation from natural ecosystems on soil organic carbon (SOC) content and density over the past 35 years. Altogether, 2140 topsoil samples (0–20 cm) were collected across Northeast China. Landsat images were acquired from 1985 to 2020 through Google Earth Engine, and the reflectance of each soil sample was extracted from the Landsat image that its time was consistent with sampling. The hybrid model that included two individual SOC prediction models for two clustering regions was built for accurate estimation after k-means clustering. The probability hybrid model, a combination between the hybrid model and classification probabilities of pixels, was introduced to enhance the accuracy of SOC mapping. Cropland reclamation results were extracted from the land cover time-series dataset at a 5-year interval. Our study indicated that: (1) Long-term use of cropland led to a 3.07 g kg⁻¹ and 6.71 Mg C ha⁻¹ decrease in SOC content and density, respectively, and the decrease of SOC stock was 0.32 Pg over the past 35 years; (2) nearly 64% of cropland had a negative change in terms of SOC content from 1985 to 2020; (3) cropland reclamation track changed from high to low SOC content, and almost no cropland was reclaimed on the “Black soils” after 2005; (4) cropland reclamation from wetlands resulted in the highest decrease, and reclamation period of years 31–35 decreased when SOC density and SOC stock were 16.05 Mg C ha⁻¹ and 0.005 Pg, respectively, while reclamation period of years 26–30 from forest witnessed SOC density and stock decreases of 8.33 Mg C ha⁻¹ and 0.01 Pg, respectively. Our research results provide a reference for SOC change in the black soil region of Northeast China and can attract more attention to the area of the protection of “Black soils” and natural ecosystems.     

Direct measurement of soil organic carbon content change in the croplands of China

Agricultural soils in China have been estimated to have a large potential for carbon sequestration, and modelling and literature survey studies have yielded contrasting results of soil organic carbon (SOC) stock change, ranging from ?2.0 to +0.6% yr^?1. To assess the validity of earlier estimates, we collected 1394 cropland soil profiles from all over the country and measured SOC contents in 2007–2008, and compared them with those of a previous national soil survey conducted in 1979–1982. The results showed that average SOC content in the 0–20 cm soil increased from 11.95 g kg^?1 in 1979–1982 to 12.67 g kg^?1 in 2007–2008, averaging 0.22% yr^?1. The standard deviation of SOC contents decreased. Four major soil types had statistically significant changes in their mean SOC contents for 0–20 cm. These were: +7.5% for Anthrosols (paddy soils), +18.3% for Eutric Cambisols, +30.5% for Fluvisols, and ?22.3% for Chernozems. The change of SOC contents showed a negative relationship with the average SOC contents of the two sampling campaigns only when soils in the region south of Yangtse River were excluded. SOC contents of the two major soil types in the region south of Yangtse River, i.e., Haplic Alisols/Haplic Acrisols and Anthrosols (paddy soils), changed little or significantly increased, though with a high SOC content. We suggest that the increase of SOC content is mainly attributed to the large increase in crop yields since the 1980s, and the short history as cropland establishment is mainly responsible for the decrease in SOC content for some soil types and regions showing a SOC decline.     

不同施肥处理对红壤性水稻土微团聚体有机碳汇的影响

在田间定位试验区 ,研究了不同施肥处理对表层红壤性水稻土微团聚体组成以及土壤有机碳在各级微团聚体中分布和赋存的影响。结果表明 ,红壤性水稻土中 0 .0 2～ 0 .0 5 mm微团聚体所占比例最大 ,达 4 0 % ;其次是 0 .0 0 2～ 0 .0 2 mm和 0 .0 5～0 .1mm的微团聚体 ;>0 .2 mm微团聚体占的比例最小。长期施用无机肥 (NPK)、有机肥 (猪粪 紫云英绿肥 ) (OM)、无机肥与有机肥配施 (NPKM) ,能显著增加 0 .0 0 2～ 0 .0 2 mm微团聚体的含量而降低 <0 .0 0 2 m m微团聚体的含量。土壤有机碳含量与0 .0 0 2～ 0 .0 2 mm微团聚体含量之间呈显著正相关关系 ;而与 <0 .0 0 2 mm微团聚体含量呈显著负相关关系。各级微团聚体有机碳含量从高到低顺序为 :>0 .2 mm,0 .1～ 0 .2 mm,<0 .0 0 2 m m,0 .0 5～ 0 .1m m,0 .0 0 2～ 0 .0 2 mm,0 .0 2～ 0 .0 5 m m。 OM、NPKM处理能显著增加 >0 .0 0 2 mm各级微团聚体有机碳的赋存量 ,新增加的有机碳主要向微团聚体 0 .1～ 0 .0 5 m m,0 .0 5～ 0 .0 2 mm和 0 .0 2～ 0 .0 0 2 mm富集 ,它们是土壤有机碳的主要载体。 3种施肥处理对提高土壤有机碳赋存效果高低顺序为 :NPKM>OM>NPK。     

Baseline map of organic carbon in Australian soil to support national carbon accounting and monitoring under climate change

We can effectively monitor soil condition—and develop sound policies to offset the emissions of greenhouse gases—only with accurate data from which to define baselines. Currently, estimates of soil organic C for countries or continents are either unavailable or largely uncertain because they are derived from sparse data, with large gaps over many areas of the Earth. Here, we derive spatially explicit estimates, and their uncertainty, of the distribution and stock of organic C in the soil of Australia. We assembled and harmonized data from several sources to produce the most comprehensive set of data on the current stock of organic C in soil of the continent. Using them, we have produced a fine spatial resolution baseline map of organic C at the continental scale. We describe how we made it by combining the bootstrap, a decision tree with piecewise regression on environmental variables and geostatistical modelling of residuals. Values of stock were predicted at the nodes of a 3‐arc‐sec (approximately 90 m) grid and mapped together with their uncertainties. We then calculated baselines of soil organic C storage over the whole of Australia, its states and territories, and regions that define bioclimatic zones, vegetation classes and land use. The average amount of organic C in Australian topsoil is estimated to be 29.7 t ha^?1 with 95% confidence limits of 22.6 and 37.9 t ha^?1. The total stock of organic C in the 0–30 cm layer of soil for the continent is 24.97 Gt with 95% confidence limits of 19.04 and 31.83 Gt. This represents approximately 3.5% of the total stock in the upper 30 cm of soil worldwide. Australia occupies 5.2% of the global land area, so the total organic C stock of Australian soil makes an important contribution to the global carbon cycle, and it provides a significant potential for sequestration. As the most reliable approximation of the stock of organic C in Australian soil in 2010, our estimates have important applications. They could support Australia's National Carbon Accounting System, help guide the formulation of policy around carbon offset schemes, improve Australia's carbon balances, serve to direct future sampling for inventory, guide the design of monitoring networks and provide a benchmark against which to assess the impact of changes in land cover, land management and climate on the stock of C in Australia. In this way, these estimates would help us to develop strategies to adapt and mitigate the effects of climate change.     

松嫩平原农田土壤有机碳变化及固碳潜力估算

基于1979—1985年全国第二次土壤普查和2015年实地采样数据,利用土壤类型法计算了近35年来松嫩平原及其各县农田表层土壤有机碳密度和土壤碳库储量;并分析了松嫩平原农田土壤有机碳密度的空间分布及变化特征;利用饱和值法对松嫩平原及其各县市农田土壤有机碳量的变化趋势进行拟合,估算其农田土壤的固碳潜力。结果表明:(1)2015年松嫩平原农田表层土壤有机碳密度平均值为1.61 kg/m~2,近35年来约有81.59%的农田土壤有机碳密度呈下降趋势,集中分布在松嫩平原北部、东部和东南部地区,以富裕县东部、依安县中部、肇东县西部、扶余县西部等地区土壤有机碳密度下降幅度最大;(2)2015年松嫩平原农田表层土壤有机碳库总储量为233.63 Tg,比全国第二次土壤普查减少了32.62 Tg;(3)2015年松嫩平原农田表层土壤总固碳潜力为-32.7 TgC,呈现出"碳源"趋势,农田土壤单位面积固碳潜力平均值为-1.793×10~(-3)Tg/km~2。     

Soil organic carbon stocks in southeast Germany (Bavaria) as affected by land use,soil type and sampling depth

Precise estimations of soil organic carbon (SOC) stocks are of decided importance for the detection of C sequestration or emission potential induced by land use changes. For Germany, a comprehensive, land use–specific SOC data set has not yet been compiled. We evaluated a unique data set of 1460 soil profiles in southeast Germany in order to calculate representative SOC stocks to a depth of 1 m for the main land use types. The results showed that grassland soils stored the highest amount of SOC, with a median value of 11.8 kg m^?2, whereas considerably lower stocks of 9.8 and 9.0 kg m^?2 were found for forest and cropland soils, respectively. However, the differences between extensively used land (grassland, forest) and cropland were much lower compared with results from other studies in central European countries. The depth distribution of SOC showed that despite low SOC concentrations in A horizons of cropland soils, their stocks were not considerably lower compared with other land uses. This was due to a deepening of the topsoil compared with grassland soils. Higher grassland SOC stocks were caused by an accumulation of SOC in the B horizon which was attributable to a high proportion of C‐rich Gleysols within grassland soils. This demonstrates the relevance of pedogenetic SOC inventories instead of solely land use–based approaches. Our study indicated that cultivation‐induced SOC depletion was probably often overestimated since most studies use fixed depth increments. Moreover, the application of modelled parameters in SOC inventories is questioned because a calculation of SOC stocks using different pedotransfer functions revealed considerably biased results. We recommend SOC stocks be determined by horizon for the entire soil profile in order to estimate the impact of land use changes precisely and to evaluate C sequestration potentials more accurately.     

Miscanthus biomass productivity within US croplands and its potential impact on soil organic carbon

Interest in bioenergy crops is increasing due to their potential to reduce greenhouse gas emissions and dependence on fossil fuels. We combined process‐based and geospatial models to estimate the potential biomass productivity of miscanthus and its potential impact on soil carbon stocks in the croplands of the continental United States. The optimum (climatic potential) rainfed productivity for field‐dried miscanthus biomass ranged from 1 to 23 Mg biomass ha^?1 yr^?1, with a spatial average of 13 Mg ha^?1 yr^?1 and a coefficient of variation of 30%. This variation resulted primarily from the spatial heterogeneity of effective rainfall, growing degree days, temperature, and solar radiation interception. Cultivating miscanthus would result in a soil organic carbon (SOC) sequestration at the rate of 0.16–0.82 Mg C ha^?1 yr^?1 across the croplands due to cessation of tillage and increased biomass carbon input into the soil system. We identified about 81 million ha of cropland, primarily in the eastern United States, that could sustain economically viable (>10 Mg ha^?1 yr^?1) production without supplemental irrigation, of which about 14 million ha would reach optimal miscanthus growth. To meet targets of the US Energy Independence and Security Act of 2007 using miscanthus as feedstock, 19 million ha of cropland would be needed (spatial average 13 Mg ha^?1 yr^?1) or about 16% less than is currently dedicated to US corn‐based ethanol production.     

Quantification of soil organic carbon sequestration potential in cropland: A model approach

Agroecosystems have a critical role in the terrestrial carbon cycling process. Soil organic carbon (SOC) in cropland is of great importance for mitigating atmospheric carbon dioxide increases and for global food security. With an understanding of soil carbon saturation, we analyzed the datasets from 95 global long-term agricultural experiments distributed across a vast area spanning wide ranges of temperate, subtropical and tropical climates. We then developed a statistical model for estimating SOC sequestration potential in cropland. The model is driven by air temperature, precipitation, soil clay content and pH, and explains 58% of the variation in the observed soil carbon saturation (n=76). Model validation using independent data observed in China yielded a correlation coefficient R ² of 0.74 (n=19, P<0.001). Model sensitivity analysis suggested that soils with high clay content and low pH in the cold, humid regions possess a larger carbon sequestration potential than other soils. As a case study, we estimated the SOC sequestration potential by applying the model in Henan Province. Model estimations suggested that carbon (C) density at the saturation state would reach an average of 32 t C ha⁻¹ in the top 0–20 cm soil depth. Using SOC density in the 1990s as a reference, cropland soils in Henan Province are expected to sequester an additional 100 Tg C in the future.     

Drivers of postfire soil organic carbon accumulation in the boreal forest

The accumulation of soil carbon (C) is regulated by a complex interplay between abiotic and biotic factors. Our study aimed to identify the main drivers of soil C accumulation in the boreal forest of eastern North America. Ecosystem C pools were measured in 72 sites of fire origin that burned 2–314 years ago over a vast region with a range of ? mean annual temperature of 3°C and one of ? 500 mm total precipitation. We used a set of multivariate a priori causal hypotheses to test the influence of time since fire (TSF), climate, soil physico‐chemistry and bryophyte dominance on forest soil organic C accumulation. Integrating the direct and indirect effects among abiotic and biotic variables explained as much as 50% of the full model variability. The main direct drivers of soil C stocks were: TSF >bryophyte dominance of the FH layer and metal oxide content >pH of the mineral soil. Only climate parameters related to water availability contributed significantly to explaining soil C stock variation. Importantly, climate was found to affect FH layer and mineral soil C stocks indirectly through its effects on bryophyte dominance and organo‐metal complexation, respectively. Soil texture had no influence on soil C stocks. Soil C stocks increased both in the FH layer and mineral soil with TSF and this effect was linked to a decrease in pH with TSF in mineral soil. TSF thus appears to be an important factor of soil development and of C sequestration in mineral soil through its influence on soil chemistry. Overall, this work highlights that integrating the complex interplay between the main drivers of soil C stocks into mechanistic models of C dynamics could improve our ability to assess C stocks and better anticipate the response of the boreal forest to global change.     

河南省土壤有机碳分布空间自相关分析

运用空间自相关方法,对河南省1958年(第1次土壤普查)和1985年(第2次土壤普查)两个时间段土壤有机碳储量分布状况进行了研究.结果表明:空间自相关指标能够比较清楚地描述河南省2次土壤普查土壤有机碳储量的地理空间变化.1958年和1985年河南省土壤有机碳总储量分别约为54·93×108t和69·65×108t,年均增长率达1%.土壤有机碳密度时空分布总趋势为豫东南角及豫西高于豫东,豫北及豫中介于两者之间;豫东南角单位面积土壤有机碳储量损失较快,最快损失速率达到年均1·57%;豫东单位面积土壤有机碳储量增加较快,最大增长速率达到年均5·27%.河南省单位面积土壤有机碳储量的时空变化与土壤初始含碳量密切相关,土壤初始含碳量越高,有机碳损失越快.     

A new baseline of organic carbon stock in European agricultural soils using a modelling approach

Proposed European policy in the agricultural sector will place higher emphasis on soil organic carbon (SOC), both as an indicator of soil quality and as a means to offset CO₂ emissions through soil carbon (C) sequestration. Despite detailed national SOC data sets in several European Union (EU) Member States, a consistent C stock estimation at EU scale remains problematic. Data are often not directly comparable, different methods have been used to obtain values (e.g. sampling, laboratory analysis) and access may be restricted. Therefore, any evolution of EU policies on C accounting and sequestration may be constrained by a lack of an accurate SOC estimation and the availability of tools to carry out scenario analysis, especially for agricultural soils. In this context, a comprehensive model platform was established at a pan‐European scale (EU + Serbia, Bosnia and Herzegovina, Croatia, Montenegro, Albania, Former Yugoslav Republic of Macedonia and Norway) using the agro‐ecosystem SOC model CENTURY. Almost 164 000 combinations of soil‐climate‐land use were computed, including the main arable crops, orchards and pasture. The model was implemented with the main management practices (e.g. irrigation, mineral and organic fertilization, tillage) derived from official statistics. The model results were tested against inventories from the European Environment and Observation Network (EIONET) and approximately 20 000 soil samples from the 2009 LUCAS survey, a monitoring project aiming at producing the first coherent, comprehensive and harmonized top‐soil data set of the EU based on harmonized sampling and analytical methods. The CENTURY model estimation of the current 0–30 cm SOC stock of agricultural soils was 17.63 Gt; the model uncertainty estimation was below 36% in half of the NUTS2 regions considered. The model predicted an overall increase of this pool according to different climate‐emission scenarios up to 2100, with C loss in the south and east of the area (involving 30% of the whole simulated agricultural land) compensated by a gain in central and northern regions. Generally, higher soil respiration was offset by higher C input as a consequence of increased CO₂ atmospheric concentration and favourable crop growing conditions, especially in northern Europe. Considering the importance of SOC in future EU policies, this platform of simulation appears to be a very promising tool to orient future policymaking decisions.     

On fertilizer‐induced soil carbon sequestration in China's croplands

Applications of fertilizer, often thought to enhance carbon sequestration in agricultural soils, are of no value to the mitigation of climate change if the carbon dioxide released during the production and distribution of nitrogen fertilizer exceeds the incremental carbon storage in soils from its use. Nitrogen fertilizer is also a source of the greenhouse gas nitrous oxide. The recent analysis of carbon sequestration in cropland soils of China does not apply these ‘discounts’ to the global warming mitigation expected from greater use of fertilizer; doing so would likely eliminate all the climate benefits of the postulated enhanced carbon sequestration.     

Land‐use conversion and changing soil carbon stocks in China's ‘Grain‐for‐Green’ Program: a synthesis

The establishment of either forest or grassland on degraded cropland has been proposed as an effective method for climate change mitigation because these land use types can increase soil carbon (C) stocks. This paper synthesized 135 recent publications (844 observations at 181 sites) focused on the conversion from cropland to grassland, shrubland or forest in China, better known as the ‘Grain‐for‐Green’ Program to determine which factors were driving changes to soil organic carbon (SOC). The results strongly indicate a positive impact of cropland conversion on soil C stocks. The temporal pattern for soil C stock changes in the 0–100 cm soil layer showed an initial decrease in soil C during the early stage (<5 years), and then an increase to net C gains (>5 years) coincident with vegetation restoration. The rates of soil C change were higher in the surface profile (0–20 cm) than in deeper soil (20–100 cm). Cropland converted to forest (arbor) had the additional benefit of a slower but more persistent C sequestration capacity than shrubland or grassland. Tree species played a significant role in determining the rate of change in soil C stocks (conifer < broadleaf, evergreen < deciduous forests). Restoration age was the main factor, not temperature and precipitation, affecting soil C stock change after cropland conversion with higher initial soil C stock sites having a negative effect on soil C accumulation. Soil C sequestration significantly increased with restoration age over the long‐term, and therefore, the large scale of land‐use change under the ‘Grain‐for‐Green’ Program will significantly increase China's C stocks.     

放牧对黄土高原退耕草地土壤有机碳储量的影响

放牧是影响草地土壤碳固存的重要因素。本研究选取黄土高原水蚀风蚀交错区西部、中部、东部地区及水蚀区,以各区20年以上退耕封禁地为对照,分析3个放牧强度下(羊粪球密度分别为0～10、10～20、>20 ind·m^-2)退耕草地0～20 cm土层土壤有机碳储量的分布特征,研究放牧及其强度对退耕草地土壤固碳效应的影响。结果表明: 放牧对交错区西部0～20 cm、东部0～10 cm,水蚀区0～5 cm土层土壤有机碳储量有显著影响,对交错区中部各土层均无显著影响;羊粪球密度0～10、＞20 ind·m^-2强度的放牧使交错区西部0～20 cm土层土壤有机碳储量显著降低了34.8%～50.9%,而在其他3个区域,放牧对有机碳储量的影响较退耕封禁地差异不显著。在交错区东部,放牧强度是影响退耕草地土壤有机碳储量的主要因素,而其他3个区域有机碳储量主要受土壤理化性质和(或)枯落物生物量的影响。羊粪球密度10～20 ind·m^-2强度的放牧对各区域退耕草地0～20 cm土层土壤有机碳储量无显著影响。     

排水对若尔盖高原泥炭地土壤有机碳储量的影响

泥炭地作为陆地上生态系统一个重要碳汇,存储了全球土壤有机碳储量的25%—43%。泥炭地排水与其他土地利用导致了大量的土壤有机碳损失。然而,有关排水对中国泥炭地土壤有机碳储量的影响研究报道较少,因此,为了获得更多可靠的泥炭地碳储量信息,以便减少它们估算的不确定性。选取了我国若尔盖高原未排水泥炭地和排水泥炭地进行土壤剖面取样,定量评价排水对泥炭地土壤有机碳储量的影响。研究表明:(1)未排水泥炭地土壤有机碳储量平均值为(923.71±107.18)t C/hm~2,为中国陆地和全球陆地土壤有机碳储量的8.1和9.4倍;而排水泥炭地土壤有机碳储量平均值为(574.01±66.86)t C/hm~2,为中国和全球陆地的5.1和5.8倍。(2)泥炭地排水后,导致表层(0—30 cm)土壤有机碳储量增加(59.11±9.31)t C/hm~2,可能源于土壤容重增加。(3)然而,完全考虑泥炭剖面深度后,排水泥炭地土壤有机碳储量较对照样地减少了349.7 t C/hm~2,这可能是由于泥炭地排水后,水位降低,加速了泥炭氧化,降低了泥炭厚度。