Changes In Soil Organic Carbon Research Articles

A dataset for soil organic carbon in agricultural systems for the Southeast Asia region

The determination of changes in soil organic carbon (SOC) content under different cropping systems is necessary for policy development oriented towards soil conservation, C sequestration, and future C credit markets. The aim of this study was to generate an open SOC dataset resulting from a systematic literature search related to the agricultural systems for Southeast Asia. The dataset has 209 articles and 4341 observations on soils of cropping systems in this region from articles published between 1987 and 2023. This dataset included different management practices, land uses, soil sampling depth, and length of SOC content assessment. In addition, inherent features of crop production reported in the experiments were included in the dataset. This dataset can be applied to quantify and compare the impact of different land uses or management practices on SOC content, providing foundational knowledge towards identifying sustainable practices. Lastly, it is a useful guide for future regional SOC sequestration policies and the development of C credit markets.

A warming climate will make Australian soil a net emitter of atmospheric CO2

Understanding the change in soil organic carbon (C) stock in a warmer climate and the effect of current land management on that stock is critical for soil and environmental conservation and climate policy. By simulation modeling, we predicted changes in Australia’s soil organic C stock from 2010 to 2100. These vary from losses of 0.014–0.077 t C ha−1 year−1 between 2020 and 2045 and 0.013–0.047 t C ha−1 year−1 between 2070 and 2100, under increasing emissions of greenhouse gases and temperature. Thus, Australian soil will be a net emitter of CO2. Depending on the future socio-economic conditions, we predict that croplands will accrue as much as 0.19 t C ha−1 year−1 between 2020 and 2045 due to their management, but accrual will decrease with warming and increased emissions by 2070–2100. The gains will be too small to counteract the losses of C from the larger areas of rangelands and coastal regions that are more sensitive to a warmer climate. In principle, prudent management of the rangelands, for example, improving grazing management and regenerating biodiverse, endemic native plant communities, could sequester more C and mitigate the loss; in practice, it may be more difficult, requiring innovation, interdisciplinary science, cultural awareness and effective policies.

Study on the Effects of Reducing Nitrogen Fertilizer: Stabilizing Yield and Carbon Sequestration by Synergistic Utilization of Chinese Milk Vetch and Rice Straw in Double-Cropping Rice Area

The excessive application of chemical fertilizers in rice fields exacerbates soil degradation and poses a threat to food security. Achieving an increase in rice production and minimizing environmental costs are inevitable requirements for achieving sustainable rice production. The synergistic utilization of rice straw (RS) and Chinese milk vetch (MV) is a sustainable measure to improve soil quality in Southern China. How this management strategy impacts agricultural productivity and soil carbon (C) sequestration under different fertilization conditions is unclear. Several treatments, including only chemical fertilizer (F), F + MV (FM), F + RS (FS), and F + MV + RS (FMS) under a standard rate of nitrogen (N100) and 40% reduced nitrogen (N60) levels were designed to explore changes in rice yields and soil organic carbon (SOC) concentrations, stocks, and soil labile organic C fractions (permanganate oxidizable C) during 2018–2020 in a double-rice-cropping system. The results show that the FMS treatment reduced soil bulk density to alleviate soil compaction and improved the soil carbon management index. The synergistic utilization of MV and RS replacing 40% of the chemical N fertilizer could still maintain the rice yield. Compared to the F treatment, the average annual grain yield was significantly increased by 9.82% and 5.84% in the FMS treatment; SOC concentration was increased by 16.05% and 19.98% on average (p < 0.05), and SOC stock was increased by 1.78 Mg C ha−1 and 2.37 Mg C ha−1 under the N60 and N100 levels, respectively. The random forest regression model and correlation analysis demonstrated that the inputs of chemical N, organic N and C, and appropriate C/N ratio promoted soil C accumulation. Furthermore, the structural equation model analysis exhibited that the C input affects the highly labile organic carbon (HLOC) and total labile organic carbon (LOC); the HLOC had a positive effect on SOC (p < 0.05). N input had a significant effect on LOC and yield. Our results suggest that the synergistic utilization of MV and RS plays an important role in ensuring stable grain production, improving soil C sequestration capacity, and maintaining soil environmental health in Southern China.

Contrasting change patterns of lignin and microbial necromass carbon and the determinants in a chronosequence of subtropical Pinus massoniana plantations

The continuous input and degradation of organic matter is crucial for soil organic carbon (SOC) sequestration during stand development. However, it remains unclear how the relative contribution of plant residues and microbial necromass to SOC changes with stand age and what are the determinants of the change pattern. The space-for-time substitution (chronosequence) approach was used to establish plots of Pinus massoniana plantations at five stand ages (6, 13, 29, 38, and 57 years). Soil samples were collected in each plot to determine the relative contribution of plant residues and microbial necromass to SOC storage by using SOC-normalized content of lignin and microbial necromass carbon (MNC). Lignin increased initially from young to mature but then decreased in over-mature plantation (R2 = 0.54, P < 0.01) and was dominated by vanillyl phenols (79 %–89 %). MNC decreased at first from young to mature but then increased in over-mature plantation (R2 = 0.50, P < 0.05) and it was dominated by fungal necromass carbon (54–63 %). Partial least squares path modeling revealed that stand age directly positively affected lignin and MNC, and indirectly maintained their change patterns through tree growth and microbial attributes. Stand age had a total positive effect (0.57) on lignin and a total negative effect (−0.54) on MNC. Regression analysis showed that the ratio of SOC to total nitrogen (SOC/TN) was positively correlated with lignin (R2 = 0.76, P < 0.01) yet negatively correlated with MNC (R2 = 0.58, P < 0.01). Additionally, the diameter at breast height, pH, and the ratio of fungal to bacterial biomass together with SOC/TN regulated the patterns of lignin and MNC with stand age. Overall, this study highlights the opposite pattern of lignin and MNC and emphasizes the importance of considering both tree growth and microbial attributes when developing SOC sequestration strategies with stand age.

Coastal reclamation alters soil organic carbon dynamics: A meta-analysis in China

As an important blue carbon pool, the content, dynamics, and related hydrological environment of coastal soil organic carbon (SOC) are extremely vulnerable to coastal reclamation; however, a full understanding of this is still lacking, mainly due to the heterogeneity in space. In this study, a dataset encompassing 680 samples gathered from 128 literatures related to SOC variation in China’s coastal areas has been constructed. Moreover, meta-analysis combined with structural equation model have been adopted to quantitatively explore the characteristics and causal mechanism of SOC change following reclamation. The results show that: (1) After reclamation, reclamation history has become an overriding control variable dominating all environmental factors, including soil physical and biochemical factors, and directly alters the content and dynamics of SOC. The SOC has tended to decrease substantially within first 10 years after reclamation and then increase significantly over time. After reclamation, forest and paddy generally have a positive effect on SOC. (2) In natural saltmarshes (before reclamation), soil biochemical factors are the dominant forces driving SOC. However, after reclamation, soil physical factors have played an increasingly important role in SOC variation, of which soil moisture is a relatively important contributor. Total nitrogen is another driving force controlling the variation of SOC acting as a gate valve role. (3) For coastal carbon sequestration, cultivating terricolous salt-tolerant vegetation to establish integrated high salinity eco-system in reclaimed zones, wetland silting promotion projects should be encouraged in natural salt marshes. And, land uses of forest and paddy should be popularized for promoting SOC in reclaimed zones.

Temporal variability is a major source of uncertainty in soil carbon measurements

AbstractMonitoring changes in soil organic carbon over time is important to many agricultural and environmental goals. Despite decades of measurements, temporal variability in soil carbon measurements has not been studied extensively. In this report, we examine five sets of monthly samples extending up to 3 years each that were collected from field experiments at four locations representative of dryland farming in the Pacific Northwest. The variance from month‐to‐month was 15%–32% of the random error, averaging 20%. This was often greater than the variance between replicate experimental units (2%–42%, averaging 17%). At certain sites, sequential samples were found to be temporally autocorrelated, but no consistent trend patterned on seasonal factors like precipitation was found. This suggests that a single point‐in‐time sample can deviate substantially from the long‐term average soil carbon at the site. We illustrate this problem with the results of repeated soil samples taken from 12 commercial farm fields. We recommend that confidence intervals for soil organic carbon estimates should include variance based on a large population of samples rather than from a single sample set at one timepoint.

Soil organic carbon increase via microbial assimilation or soil protection against the priming effect is mediated by the availability of soil N relative to input C

Labile C inputs into soils will be partially transformed into soil organic carbon (SOC) through microbial assimilation or physicochemical protection as such mineral-organic interactions and soil aggregation. The C inputs may stimulate the decomposition of native SOC, inducing a phenomenon known as the priming effect. Increasing C inputs may increase SOC content, yet the relative role of these mechanisms in controlling the magnitudes of SOC increase among soils remains unclear. Four soils differing in microbiology and N content were incubated with 13C-labeled glucose at the amounts of 0.5 (G0.5), 1.0 (G1.0), and 2.0 (G2.0) g C kg−1 soil for 48 days. The objectives of this study were 1) to quantify the fates of added glucose-C, the priming effect, and the changes in SOC and mineral N contents after the incubation, and 2) to identify the main mechanisms for SOC increase with the increased amount of C input and the effects of initial soil N availability and microbial composition. 13C isotope probing showed that 19 to 26 % and 37 to 96 % of added glucose were utilized for microbial respiration and growth, respectively, after the incubation in all soils, with the glucose-C use efficiency ranging from 30 to 60 %. The remaining accounted for 4 to 37 % in all cases except for UltisolHN at G1.0 and G2.0 (–23 % and −2%), which was confirmed as the fraction protected in soil or re-utilized by microbes via acid extraction. The soil-protected glucose-C was higher, while glucose-C use efficiency was lower with the increased amount of added glucose only in the soils with low N. Glucose addition induced a positive priming effect, a SOC increase, and a mineral N loss irrespective of soil type and addition amount. Glucose addition increased the cumulative fungal biomass in all cases and the cumulative bacterial biomass only at G2.0 in all soils and at G1.0 in the high-N soils. It increased the final fungal necromass only at G0.5 in MollisolLN and UltisolHN and at G2.0 in MollisolHN and the final bacterial necromass in all cases except for the low-N soils and UltisolHN at G2.0. With the increased amount of added glucose, the SOC content increased linearly and the priming effect and fungal biomass increased non-linearly, with larger magnitudes in the soils with lower N. These results indicated that glucose was quickly protected after addition and remained in the soil until soil N became a limiting factor for microbial utilization. The availability of soil N relative to input C mediated microbial growth and its controls over SOC change via the soil protection and priming effects. The carbon sequestration potential with increased input of dissolved substrates as such glucose e. g. through root exudation was likely larger in soils with lower fertility due to reduced substrate-C use efficiency and increased effect of soil protection despite an increased priming effect. Further studies are needed on more substrate types as they affect substrate-C use efficiency and soil protection mechanisms.

Predicting soil organic carbon content using simulated insitu spectra and moisture correction algorithms in southern Xinjiang, China

Soil organic carbon (SOC) is an essential component of the terrestrial carbon pool, and changes in SOC are critical to ecosystem stability and agricultural production. In-situ field spectroscopy, such as visible and near-infrared (vis-NIR) spectroscopy, has proven to be an ideal tool to achieve rapid and efficient detection of SOC. However, soil moisture interference is one of the main challenges for the measurement of SOC using in-situ spectroscopy. Great progress has been made in using external parameter orthogonalization (EPO), direct standardization (DS) and piecewise direct standardization (PDS) to remove the influence of moisture on using vis-NIR spectroscopy to predict SOC. However, most current studies were conducted based on a certain moisture, which makes it difficult to provide a comprehensive guide for SOC detection using in situ spectroscopy. In this study, 135 surface (0–20 cm) soil samples were collected from the Aksu region of Xinjiang, northwestern China. The soil samples were wetted to a saturated moisture content state after manual removal of salts. The spectra data of 11 different moisture levels during natural air-drying of the wet soil samples were measured to analyze and compare the performance of three algorithms, EPO, DS and PDS, in removing the effect of moisture and improving the accuracy of SOC prediction. The results show that PDS has a relatively poor ability to remove the effect of moisture among the three moisture correction algorithms. When the moisture content of the soil exceeds 48%, EPO, DS and PDS cannot effectively remove the disturbance of moisture. The EPO algorithm was the most effective in removing moisture effects when the soil moisture content (SMC) was 25–48%. Using EPO, the predicted R2 and RPIQ of SOC increased by >0.19 and 0.87, respectively. The DS algorithm was the best method to remove the moisture effect on soil vis-NIR spectra when the SMC was 6–25%, and the R2 and RPIQ predictions of SOC after removing the effect of moisture by DS increased by >0.09 and 0.87, respectively. However, when the moisture content is <6%, the influence of soil moisture on the prediction accuracy of SOC spectra is negligible, and SOC can be predicted with high accuracy using in-situ spectra without the introduction of moisture correction algorithms. An appropriate moisture correction algorithm should be selected to remove moisture interference according to the SMC condition.

Microbial mediation of soil carbon loss at the potential climax of alpine grassland under warming

Soil in high latitude and altitude cold regions contains over half of soil organic carbon (SOC) globally, so the decomposition of these SOCs under climate warming could release huge amounts of carbon dioxide to the atmosphere, amplifying climate warming. However, it is still unclear how the SOC storages will change when the ecosystem reaches the final and stable stage (i.e., the climax) under long-term warming. This is mainly because the turnover times of SOC in cold regions exceeds hundreds or even thousands of years, much longer than the periods of simulated warming experiments. Herein we used natural geothermal warming gradients in a Tibetan alpine grassland to determine SOC changes and underlying plant and microbial mechanisms at the potential climax. SOC concentrations were significantly decreased by 21.4%–30.6% under high-level soil warming (+4∼+6 °C), but remained unchanged under low-level soil warming (+2 °C). The losses of SOC were primarily from mineral-associated organic carbon, rather than unprotected particulate organic carbon. The shifts of microbial communities and associated decline of microbial carbon use efficiency, rather than plant-driven carbon fluxes, substantially contributed to the SOC changes. This observed SOC losses at the climax of alpine grassland by high-level warming provide strong empirical support for the positive soil carbon-climate feedback in cold regions, which could not be concluded from short-term experiments or only based on ecosystem carbon fluxes alone. The divergent responses of SOC to different degrees of warming suggest that models must account for these heterogeneous carbon dynamics for projecting future climate warming scenarios.

The influence of grazing intensity on soil organic carbon storage in grassland of China: A meta-analysis

Grazing can potentially affect grassland soil carbon storage through selective feeding, trampling and fecal excretion of livestock. The numerous case studies and a few meta-analyses have focused on grazing-induced changes in soil organic carbon (SOC) storage, but the effects of grazing on SOC in major grassland types of China are not clear. In this study, we performed a comprehensive meta-analysis to identify the impact of grazing on soil carbon in China. We found that the key factors affecting the SOC content of grazing grasslands is grazing intensity. Heavy grazing (HG) significantly decreased the SOC content by 7.5 % in major grassland types of China (95 % confidence interval (CI), −11.43 % to −3.57 %, P < 0.001). The SOC content in temperate desert steppes (7.22 %), temperate meadow-steppes (10.89 %) under heavy grazing (HG) showed significantly (P < 0.05) decreased. HG resulted in significant (P < 0.01) decreases in SOC content (6.91 %) of Kastanoze. Our study highlighted that formulating rational grazing strategies according to grassland and soil types was the key to increasing SOC storage and sequestration under climate change and increased human pressure.

Harvest residues: A relevant term in the carbon balance of croplands?

Over the past two decades, major efforts have been made to quantify the extent to which and under what conditions croplands are sources or sinks for carbon. For this purpose, the net carbon stock change of the study site is typically quantified based on net CO2 fluxes monitored with an eddy covariance or chamber system, on measured C import by organic fertilizer and C export by harvest. While in cropland studies this balance is usually referred to as net biome productivity (NBP), we prefer to use the term net ecosystem carbon balance (NECB) here. NECB is basically the sum of the stock change of plant carbon (ΔPC) and soil organic carbon (ΔSOC). In the standard approach, the assumption is that at an annual cropland site the bulk of plant biomass is typically removed at harvest, and that ΔPC can therefore be neglected. In this case, ΔSOC equals NECB. In this paper we show that this assumption is problematic, particularly if in crop rotation systems the budget is determined over a single cropping period. The present contribution extends the concept of NECB to include harvest residues (HR) and applies it to a case study over a maize - winter wheat - winter wheat rotation at a cropland site in southwest Germany. In all three cropping periods, the sign of NECB was opposite that of ΔSOC. Accordingly, neglecting HR led to an incorrect result concerning the question whether the site is a sink or a source for soil carbon. Our findings demonstrate that for croplands HR must be included to obtain an accurate and meaningful carbon balance.

Optimizing the rate of straw returning to balance trade-offs between carbon emission budget and rice yield in China

Rice paddies are a prominent contributor to greenhouse gases (GHGs) emissions, accounting for 22 % of the overall agricultural methane (CH4) emissions. Although returning rice straw to the field can increase yield and soil organic carbon (SOC), the significant GHGs released during this process often negate these positive effects. Thus, understanding the impact of straw returning on the relationship between rice yield and GHGs is crucial for farming adaptation and climate change mitigation. This study aims to investigate the effects of varying straw returning rates on rice yield and GHGs in China and identify the optimal rates on a provincial scale. This study utilized county-level meteorological, soil, and field management data. The Dynamic Nitrogen and Carbon Model (DNDC) model was used to simulate the impacts on rice yield, GHGs, and SOC changes under different straw returning rates in China from 2010 to 2022, including no straw, 1/3, 2/3, and full straw returning. The results showed that 1/3, 2/3, and full straw incorporation increased rice yield per unit area by 1.07 %, 2.25 %, and 3.26 % for single rice cropping, 1.10 %, 2.24 %, and 3.52 % for early rice, and 1.92 %, 3.91 %, and 5.95 % for late rice, respectively. Compared with no straw returning, the total SOC content (0–50 cm) increased by 3.88 % (78.07 Tg), 7.75 % (156.09 Tg), and 11.65 % (234.62 Tg) under 1/3, 2/3, and full straw returning, respectively. However, the total GHGs were increased by 23.32 %, 43.50 %, and 61.48 % for 1/3, 2/3, and full straw incorporation compared to no straw returning. While the overall benefits of straw returning varied across regions, in certain areas like northeastern China, Xinjiang, and Yunnan, an increase in straw returning rates leads to a significant increase in yield with a relatively smaller increase in GHGs. This can be attributed to factors such as lower temperatures, decreased SOC, and lower soil pH, restricting CH4 production. Conversely, in regions with higher soil pH, such as north China and the Sichuan Basin, as well as in warmer southern areas, the increase in GHGs is quite pronounced. In summary, implementing straw returning significantly increases rice production and SOC but simultaneously increases GHGs. In China, the most widespread utilization of rice straw remains straw returning. We have summarized the average impact of straw returning on yield, SOC, and GHGs, and proposed straw returning rates tailored to the comprehensive benefits in different regions, to enhance the carbon sequestration and emission reduction rate of rice straw returning.

Response of maize yield to changes in soil organic matter in a Swedish long‐term experiment

AbstractAgricultural practices that lead to soil carbon sequestration may be a win–win strategy for mitigating global warming and improving soil fertility and resource use efficiency. The mechanisms through which soil organic carbon (SOC) concentration affects crop yields are numerous but difficult to separate. The objective of this study was to disentangle these processes and estimate to what extent the yield response to SOC is mainly driven by changes in physical or biochemical properties and processes. This was achieved by analysing the response of yields in continuous maize to SOC concentrations during 20 years (2000–2019), which had evolved in 14 experimental treatments in a Swedish long‐term field experiment at Ultuna since 1956, ranging from 0.94% to 3.65% in the topsoil (0–20 cm). Average maize yields during this period varied between 1.9 and 8.4 Mg dry mass per hectare in the different treatments. The treatments comprise applications of different mineral nitrogen (N) fertilizers and organic amendments and combinations thereof. Our analysis showed that maize yield in the treatments that were not severely limited by nitrogen supply or soil acidity increased by 16% for each percentage unit increase in SOC. We applied the widely used concept of critical N concentration in plant biomass to diagnose the N status in maize in the different treatments (N nutrition index [NNI]) and parameterized a response function between yield and pH (RpH). Dry soil bulk density (BD) was used as a proxy for soil physical properties. These three variables NNI, RpH and BD explained 95% of the variation in maize yields among treatments. Further analysis of the relationship between BD, SOC and plant available water capacity revealed that about two thirds of the yield increases in response to SOC change could be ascribed to associated changes in soil physical properties. Our analysis suggests that the extra storage capacity of water, which increased by up to 15 mm in the topsoil for each unit percentage increase in SOC, was the main driver for the observed yield responses. We conclude that measures for increasing SOC in soils most likely are an effective adaptation strategy for reducing the risk of crop damage during dry spells, which probably are becoming more frequent in the future due to climate change, even in relatively humid climates as in Sweden.

Urbanization-induced soil organic carbon loss and microbial-enzymatic drivers: insights from aggregate size classes in Nanchang city, China.

Soil microorganisms and enzymes play crucial roles in soil organic carbon (SOC) sequestration by promoting soil aggregate formation and stability and by participating in SOC cycling and accumulation. However, the effects by which soil microorganisms and enzymes act as mediators driving dynamic changes in SOC during rapid urbanization remain unclear. Therefore, this study selected the built-up area of Nanchang City, China (505 km2), as the study area. Sampling surveys were conducted using 184 sample plots stratified based on the proportion of impermeable surface area to distinguish different urbanization levels. The driving factors of dynamic changes in SOC of different aggregates during the process of urbanization were analyzed using the soil microbial community and enzyme activities. The results demonstrated that with an increase in urbanization intensity, both SOC content and stock exhibited a significant decline (p < 0.05). The highest SOC stock and contribution rate were observed in the 0.25-1 mm aggregates, and they were significantly influenced by urbanization (p < 0.05). In addition, the biomass of gram-positive bacteria (G+) and actinomycetota, and the activities of N-acetylglucosaminidase and acid phosphatase (AP) were significantly higher in low-urbanization areas than in high-urbanization areas (p < 0.05). SOC of each aggregate was positively correlated with fungi, arbuscular mycorrhizal fungi, G+, gram-negative bacteria, actinomycetota, protozoa, β-1,4-glucosidase, N-acetylglucosaminidase, AP, urease, and catalase. Compared to soil enzymes, soil microorganisms exhibited a greater role in SOC sequestration (22.7%). Additionally, a structural equation model indicated that urbanization can directly or indirectly lead to a decrease in SOC of aggregates by altering soil physicochemical properties and affecting microbial and enzyme dynamics. However, the larger vegetation characteristics index mitigate the negative impacts of urbanization on SOC. Overall, urbanization had a negative impact on soil carbon storage. In the future, it is important to consider strategies that focus on improving soil nutrients, maintaining soil structure, protecting existing urban trees, and enhancing plant diversity during the urbanization process. These measures can help increase soil microbial biomass and enzyme activity, thereby improving soil and aggregate-related SOC content. The study could contribute to enhancing carbon sequestration in urban greenspaces.

Carbon Farming practices assessment: Modelling spatial changes of Soil Organic Carbon in Flanders, Belgium

Carbon sequestration in soils is a strategy to mitigate climate change and promote sustainable soil management. Since the European Union (EU) stimulates the reduction of greenhouse gases (GHG) from the atmosphere, the necessity to explore innovative approaches to sequester carbon in agricultural landscapes is becoming urgent. Carbon Farming (CF) has emerged as a promising program to mitigate climate change in agriculture but there is still a lack of agreement on which tools can be used to calculate Soil Organic Carbon (SOC) dynamics in this context. Using the RothC model a spatial analysis of SOC in the agricultural parcels of Flanders, Belgium was performed. Two among the various CF practices were simulated: a use of cover crops (CC) and the most common crop rotations adopted in the area, enriched with the use of cover crops. The performances of the model were evaluated and compared to other studies in areas with similar climate and environments. The selected CF practices can mitigate the carbon emissions from agricultural soils up to 60 % of the current projections. The most sensitive variables in the RothC model that affect the final total SOC, and thus determining the model outcome, are the Business As Usual (BAU) carbon inputs and the initial carbon content. For these variables the Pearson Correlation Coefficient with the change in SOC reached values of −0.78 and −0.50 respectively. To achieve net carbon sequestration in the agricultural soils of Flanders, Belgium, more effective solutions need to be evaluated. Furthermore, a larger amount and accessibility of data are required to reach better modelling performances.

A meta-analysis reveals increases in soil organic carbon following the restoration and recovery of croplands in Southwest China.

In China, the Grain for Green Program (GGP) is an ambitious project to convert croplands into natural vegetation, but exactly how changes in vegetation translate into changes in soil organic carbon remains less clear. Here we conducted a meta-analysis using 734 observations to explore the effects of land recovery on soil organic carbon and nutrients in four provinces in Southwest China. Following GGP, the soil organic carbon content (SOCc) and soil organic carbon stock (SOCs) increased by 33.73% and 22.39%, respectively, compared with the surrounding croplands. Similarly, soil nitrogen increased, while phosphorus decreased. Outcomes were heterogeneous, but depended on variations in soil and environmental characteristics. Both the regional land use and cover change indicated by the landscape type transfer matrix and net primary production from 2000 to 2020 further confirmed that the GGP promoted the forest area and regional mean net primary production. Our findings suggest that the GGP could enhance soil and vegetation carbon sequestration in Southwest China and help to develop a carbon-neutral strategy.

Sensitivity of streamflow and nutrient loads to changes in leaf area index and soil organic carbon in a sub-tropical catchment subject to climate change

Study regionThe Upper Nerang River Catchment located in South-East Queensland (SEQ), Australia. Study focusThe Soil Water Assessment Tool (SWAT) model was applied to Upper Nerang River Catchment to test the sensitivity of catchment runoff and water quality to changes in Leaf Area Index (LAI) and Soil (topsoil) Organic Carbon (SOC) associated with climate change. These parameters are normally considered to be stationary in hydrological models, potentially constraining the accuracy of these models for catchment simulation under future climate scenarios. New hydrological insights for the regionLAI decreased by 0.4% to 16.9% and SOC by 5.9 to 11.6%, depending on land cover, future period, and emission scenario. Climate change scenarios showed an increase in extreme flows compared with a baseline (recent historical) case and were characterised by reduced return period and greater magnitude of discharge. Changes in LAI and SOC have the potential to mitigate these changes and may reduce loads of SS, TN and TP under future climate change scenarios. The findings of this study indicate that incorporating changes in LAI and SOC into hydrological models is important for modelling the catchment response to climate change. Furthermore, LAI and SOC could be managed to mitigate impacts of climate change on streamflow and losses of SS, TN and TP from catchment soils to receiving waters.

Balancing Non‐CO2 GHG Emissions and Soil Carbon Change in U.S. Rice Paddies: A Retrospective Meta‐Analysis and Agricultural Modeling Study

AbstractU.S. rice paddies, critical for food security, are increasingly contributing to non‐CO2 greenhouse gas (GHG) emissions like methane (CH4) and nitrous oxide (N2O). Yet, the full assessment of GHG balance, considering trade‐offs between soil organic carbon (SOC) change and non‐CO2 GHG emissions, is lacking. Integrating an improved agroecosystem model with a meta‐analysis of multiple field studies, we found that U.S. rice paddies were the rapidly growing net GHG emission sources, increased 138% from 3.7 ± 1.2 Tg CO2eq yr−1 in the 1960s to 8.9 ± 2.7 Tg CO2eq yr−1 in the 2010s. CH4, as the primary contributor, accounted for 10.1 ± 2.3 Tg CO2eq yr−1 in the 2010s, alongside a notable rise in N2O emissions by 0.21 ± 0.03 Tg CO2eq yr−1. SOC change could offset 14.0% (1.45 ± 0.46 Tg CO2eq yr−1) of the climate‐warming effects of soil non‐CO2 GHG emissions in the 2010s. This escalation in net GHG emissions is linked to intensified land use, increased atmospheric CO2, higher synthetic nitrogen fertilizer and manure application, and climate change. However, no/reduced tillage and non‐continuous irrigation could reduce net soil GHG emissions by approximately 10% and non‐CO2 GHG emissions by about 39%, respectively. Despite the rise in net GHG emissions, the cost of achieving higher rice yields has decreased over time, with an average of 0.84 ± 0.18 kg CO2eq ha−1 emitted per kilogram of rice produced in the 2010s. The study suggests the potential for significant GHG emission reductions to achieve climate‐friendly rice production in the U.S. through optimizing the ratio of synthetic N to manure fertilizer, reducing tillage, and implementing intermittent irrigation.

Microbial-driven mechanisms for the effects of heavy metals on soil organic carbon storage: A global analysis

Heavy metal (HM) enrichment is closely related to soil organic carbon (SOC) pools in terrestrial ecosystems, which are deeply intertwined with soil microbial processes. However, the influence of HMs on SOC remains contentious in terms of magnitude and direction. A global analysis of 155 publications was conducted to integrate the synergistic responses of SOC and microorganisms to HM enrichment. A significant increase of 13.6 % in SOC content was observed in soils exposed to HMs. The response of SOC to HMs primarily depends on soil properties and habitat conditions, particularly the initial SOC content, mean annual precipitation (MAP), initial soil pH, and mean annual temperature (MAT). The presence of HMs resulted in significant decreases in the activities of key soil enzymes, including 31.9 % for soil dehydrogenase, 24.8 % for β-glucosidase, 35.8 % for invertase, and 24.3 % for cellulose. HMs also exerted inhibitory effects on microbial biomass carbon (MBC) (26.6 %), microbial respiration (MR) (19.7 %), and the bacterial Shannon index (3.13 %) but elevated the microbial metabolic quotient (qCO2) (20.6 %). The HM enrichment-induced changes in SOC exhibited positive correlations with the response of MBC (r = 0.70, p < 0.01) and qCO2 (r = 0.50, p < 0.01), while it was negatively associated with β-glucosidase activity (r = 0.72, p < 0.01) and MR (r = 0.39, p < 0.01). These findings suggest that the increase in SOC storage is mainly attributable to the inhibition of soil enzymes and microorganisms under HM enrichment. Overall, this meta-analysis highlights the habitat-dependent responses of SOC to HM enrichment and provides a comprehensive evaluation of soil carbon dynamics in an HM-rich environment.

Nine years of warming and nitrogen addition in the Tibetan grassland promoted loss of soil organic carbon but did not alter the bulk change in chemical structure

Abstract. Nitrogen (N) and warming effects on ecosystem carbon (C) budgets and stabilization are critical to understand as C sequestration is considered as a mechanism to offset anthropogenic CO2 emissions, which is important for accurately predicting ecosystem C sequestration and/or potential C loss, remaining controversial though. However, the relevant information, especially for the intervention of environmental controls on grassland soil, is limited in Tibetan Plateau (TP) regions. Here we used a 9-year two-way factorial experiment involving warming with open top chambers (+1.80 ∘C in the daytime and +0.77 ∘C in the nighttime at the soil surface) and multilevel nitrogen (N) enrichment treatments (0, 5, 10, and 15 gm-2yr-1) in the TP to investigate the changes in soil organic carbon (SOC) pool size and chemical structure. Nine-year warming treatment significantly decreased SOC stock in the Tibetan grassland. We observed decreasing SOC concentrations which may be related to changes in the C-degrading enzymes. Surprisingly, the SOC molecular structure remained unchanged in all N-enrichment and warmed plots, suggesting that both treatments had affected all forms of SOC, from simple and complex polymeric in a similar way. Our results suggest that long-term warming stimulates soil C loss but no preference in SOC loss with different chemical structures.