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Background and aims: The accumulation of soil organic carbon (SOC) is a crucial process in mitigating climate change and ensuring soil quality. Subtropical plantations in China have shown high potential for enhancing SOC sequestration due to their high carbon sink capacity. However, the dynamics and compositions of SOC after long term afforestation are still poorly understood. Methods: We examined the dynamics of SOC and its fractions of different soil layers (0–5 cm, 5–10 cm, 10–20 cm, 20–40 cm, 40–80 cm, 80–100 cm) in a mixed broadleaf-conifer plantation (BCP), a Masson pine plantation (MP), and a Slash pine plantation (SP), and an enclosed forest (EF) in subtropical China. Both physical fractions (particulate organic carbon (POC), soil clay organic carbon (SOCclay), soil silt organic carbon (SOCsilt)) and chemical fractions (iron-aluminum-bound organic carbon (Fe/Al-OC), and calcium-bound organic carbon (Ca-OC)) were determined. Additionally, soil physicochemical properties were further analyzed. Results: Our results showed the SOC storage in the EF, BCP, MP, and SP in 2019 increased by 82%, 238%, 126%, and 103% respectively compared to 1984. The proportions of MAOC to SOC were respectively as follows: SP (65.9%) > BCP (64.9%) > EF (61.6%) > MP (53.9%). The mean proportions of SOCclay to MAOC were as follows: BCP (71.1%) > EF (66.9%) > MP (58.5%) > SP (51.0%). The mean proportions of Fe/Al-OC to MAOC were as follows: EF (53.3%) > SP (48.3%) > MP (47.9%) > BCP (39.8%). All these proportion increased with soil depth. RDA and PLS-SEM analysis revealed that soil nitrogen content and electrochemical properties (pH and EC) were the main factors that controlled SOC content and fractions. Conclusions: Subtropical plantations have significant soil carbon sequestration capabilities, but they are currently nearing saturation. Soil nitrogen content may be key factor limiting further enhancement of carbon sequestration. Due to the high proportion of MAOC and relative consistent SOC storage, BCP and SP are recommended as priorities for plantation regeneration in subtropical China. [ABSTRACT FROM AUTHOR]

Water-level fluctuation (WLF) can destroy soil aggregates and induce soil organic carbon (SOC) loss, potentially triggering impacts on the concentration of atmospheric carbon dioxide. However, responses of soil aggregate content and aggregate-associated organic carbon to WLF have not been well studied, especially in the water-level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR). Therefore, samples from different elevations (145 m, 155 m and 165 m) in the WLFZ of the TGR were collected for experiments. The wet sieving method was used to divide soil into silt and clay (<0.053 mm), micro-aggregate (0.053–0.25 mm) and macro-aggregate (>0.25 mm). The K2Cr2O7-H2SO4 oxidation method was used to measure total SOC content in different soil aggregates. A modified Walkley and Black method was used to measure labile carbon in different soil aggregates. Results showed that macro-aggregate content substantially decreased, while micro-aggregate content remained stable and silt and clay fraction accumulated with a decrease in water-level elevations. Moreover, total SOC content and labile carbon in macro-aggregate were obviously higher than those in the micro-aggregate and the silt and clay fraction. Macro-aggregate contributed the most to SOC sequestration, while micro-aggregate contributed the least, and the contribution of macro-aggregate increased with a decrease in water-level elevations. We concluded that the macro-aggregate was the most active participant in the SOC sequestration process, and preferentially increasing the macro-aggregate content of the lowest water-level elevation was conducive to an improvement in soil carbon sequestration potential and would mitigate climate change. [ABSTRACT FROM AUTHOR]

Soil parent material can strongly influence soil's physical and chemical properties, significantly affecting soil organic carbon (SOC) stabilization. However, the importance of different soil parent materials on the amount and composition of subsoil carbon in subtropical soils remains poorly qualified. Subsoil SOC (below A horizon) is chosen for this study because of its higher proportion of stable carbon than surface soils in A horizon. Here, we investigated the dependence of soil mineral‐associated organic carbon (MAOC) and its three mineral‐stabilized fractions on soil physical and chemical parameters (clay content, cation exchange capacity (CEC) and metal oxides) in the subsoil soil (B and C horizons) originating from three contrasting parent materials (sandshale, granite, limestone). The results showed that MAOC accounts for an average of 88% of total SOC, of which organo‐metal complexes (extracted with sodium pyrophosphate) are the dominant form at all three sites. MAOC and its three fractions were significantly correlated with soil clay, CEC, sodium pyrophosphate extractable Fe and oxalate extractable Fe concentrations (P < 0.05), which varied significantly with soil parent material. Since the sodium pyrophosphate plus oxalate‐ extracted mineral‐associated carbon accounted for more than 70% of MAOC, and the molar ratio between sodium pyrophosphate or oxalate‐ extracted mineral‐associated carbon and Fe (C:Fe) ranged from 2.7 to 17.1. The formation of Fe‐associated organic complex is dominated by co‐precipitation when C:Fe is >1. Therefore we conclude that non‐sorptive interactions with the mineral phase through co‐precipitation are the dominant mechanism for SOC stabilization in subtropical forest soils. Plain Language Summary: Identifying the mechanisms for the accumulation and stabilization of forest soil organic carbon (SOC) is particularly important for increasing land‐based carbon mitigation as a part of the solution toward carbon neutrality by 2060 in China. However, our understanding of the mechanism of SOC stabilization is still limited, particularly how soil carbon stabilization is influenced by soil parent material, which has been shown to have strong influences on soil's physical and chemical properties, therefore on SOC stabilization. By analyzing the carbon content and composition of the soils developed from the different parent materials, we showed that soil parent material indirectly affected SOC through soil physical and chemical properties, of which soil clay content, CEC and soil Fe oxides played an important role in SOC stabilization. Both sorptive and co‐precipitation interactions between Fe and SOC contributed to SOC stabilization in subtropical forest soil with co‐precipitation as the dominant mechanism. Key Points: Mineral‐associated organic carbon accounts for >80% of soil organic carbon (SOC) in southern China forest soilsCo‐precipitation with Fe is the dominant SOC stabilization mechanismParent material is a significant contributor to the observed SOC variations [ABSTRACT FROM AUTHOR]

[Display omitted] • Invasion by Spartina increased mineral-bound OC in mudflat soil. • Subsequently reclamation for aquaculture decreased soil mineral-bound OC. • Mineral-bound OC was correlated to nitrogen supply and soil clay content. • Habitat change affected Fe[Al]–OC more than Ca-OC and residual-OC. • Soil OC storage increased more strongly with increasing Ca-OC. The formation of mineral-bound organic carbon (OC) complexes is important for the long-term preservation of soil organic carbon (SOC) in wetlands. Many coastal wetlands globally have been threatened by plant invasion and land development, but information on the effects on mineral-bound OC is limited. We measured the soil contents of Ca-OC, Fe(Al)–OC and residual OC across 21 coastal wetlands in southern China that have gone through the same sequence of land cover change, from native mudflats (MFs) to Spartina alterniflora marshes (SAs) then to earthen aquaculture ponds (APs). Residual-OC was the main component of SOC (74.1–78.2 %), followed by Fe(Al)–OC (18.4–22.8 %) and Ca-OC (<3.5 %). All three components in the soil increased when MFs were converted to SAs, but decreased in subsequent conversion of SAs to APs. Land cover change affected Fe(Al)–OC the most, but SOC storage increased more strongly with increasing Ca-OC. Nitrogen supply in the form of NH 4 +-N and clay content both positively affected the changes in mineral-bound OC. Our results suggest that different land cover change scenarios had different effects on the amounts of mineral-bound OC and their liability to microbial turnover, resulting in different degrees of SOC preservation and carbon emissions. [ABSTRACT FROM AUTHOR]

• Patchiness caused significant reduction of SOC and TN stocks. • Reduced vegetation input and increased erosion output accounted for SOC and TN loss. • Grasslands with high patchiness had a great potential for C and N sequestration. Patchiness acts as an indicator of terrestrial ecosystem degradation and can lead to considerable loss of soil organic carbon and total nitrogen. However, quantitative assessments of the effects of patchiness on soil organic carbon and total nitrogen stocks and their associated mechanisms remain limited. This study aimed to explore the influence mechanisms of patchiness on soil organic carbon and total nitrogen stocks and to project the quantitative contribution of the further expansion of patchiness and vegetation recovery. Soil properties, soil organic carbon and total nitrogen stocks were investigated using a combination of field sampling and aerial photography in four grassland types, alpine meadow, alpine steppe, temperate grassland, and desert grassland, at 47 sites in northwestern China. Soil organic carbon and total nitrogen densities in the bare patches were 34–54 % and 23–41 % lower, respectively, compared to the original vegetation. At the plot-scale, current soil organic carbon and total nitrogen stocks ranged from 30.85 to 77.80 T/ha and 3.26 to 10.19 T/ha, respectively, across grassland types; with a 10–27 % and 7–24 % potential loss of soil organic carbon and total nitrogen stocks, respectively, from the further expansion of patchiness but a 10–50 % and 9–37 % potential increase in soil organic carbon and total nitrogen stocks, respectively, from vegetation recovery. Soil organic carbon and total nitrogen stocks were positively correlated with vegetation biomass, soil clay content, and precipitation (p < 0.001), whereas they were negatively correlated with patchiness (p < 0.001). In summary, patchiness reduced soil organic carbon and total nitrogen stocks by decreasing vegetation inputs and increasing erosion outputs, while vegetation recovery showed potential for increasing carbon and nitrogen stocks. Our results highlight that maintaining intact vegetation cover is critical for preserving terrestrial ecosystem carbon and nitrogen storage. [ABSTRACT FROM AUTHOR]

Background: Forest restoration has been considered an effective method to increase soil organic carbon (SOC), whereas it remains unclear whether long-term forest restoration will continuously increase SOC. Such large uncertainties may be mainly due to the limited knowledge on how soil microorganisms will contribute to SOC accumulation over time. Methods: We simultaneously documented SOC, total phospholipid fatty acids (PLFAs), and amino sugars (AS) content across a forest restoration gradient with average stand ages of 14, 49, 70, and > 90 years in southern China. Results: The SOC and AS continuously increased with stand age. The ratio of fungal PLFAs to bacterial PLFAs showed no change with stand age, while the ratio of fungal AS to bacterial AS significantly increased. The total microbial residue-carbon (AS-C) accounted for 0.95–1.66 % in SOC across all forest restoration stages, with significantly higher in fungal residue-C (0.68–1.19 %) than bacterial residue-C (0.05–0.11 %). Furthermore, the contribution of total AS-C to SOC was positively correlated with clay content at 0–10 cm soil layer but negatively related to clay content at 10–20 cm soil layer. Conclusions: These findings highlight the significant contribution of AS-C to SOC accumulation along forest restoration stages, with divergent contributions from fungal residues and bacterial residues. Soil clay content with stand age significantly affects the divergent contributions of AS-C to SOC at two different soil layers. [ABSTRACT FROM AUTHOR]

Ecological restoration is considered an effective strategy for increasing soil carbon storage and mitigating climate change. However, the impact of revegetation in desert areas on the stability of soil organic carbon (SOC) is still unclear. We investigated the content and stability of SOC in restoration sites along a chronosequence in the Tengger Desert, focusing on the mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) fractions. The content of SOC significantly increased with site age from 0.37 g kg−1 at year 0–5.32 g kg−1 at year 66. Revegetation significantly changed the SOC fraction and improved SOC stability as a factor of site age. In the 66-year-old site, the levels of MAOC and POC were increased by 255.67 and 9.24 times, respectively. The percentage of MAOC was increased from 1.50% to 28.92%, whereas that of POC was decreased from 98.50% to 71.08%. Based on our findings, the content and proportion of MAOC and POC are closely related to plant input, soil variables, and the soil microbial community. We estimate that the maximum content and proportion of MAOC are 2.65 g kg−1 and 36.71% with continuous succession, based on the soil clay and silt contents. Overall, revegetation improved the stability of SOC. Our study highlights the importance of the revegetation of temperate desert areas to further mitigate climate change. [Display omitted] • Revegetation significantly changed the SOC fraction and improved SOC stability as a factor of stand age. • Revegetation increased the content and proportion of MAOC, whereas it increased POC content while decreasing its proportion. • The MAOC and POC are closely related to plant input, soil variables, and the soil microbial community. • The maximum content and proportion of MAOC are 2.65 g kg−1 and 36.71% with continuous succession. [ABSTRACT FROM AUTHOR]

Purpose: Soil organic carbon (SOC) dynamics are central to understanding the effects of environmental change on the carbon cycle of ecosystems. Vegetation and soil stable carbon isotope composition (δ13C), especially the difference of δ13C between surface soils and source vegetation (Δδ13C), can provide useful information about the SOC dynamics. The variations and patterns of vegetation and soil δ13C and Δδ13C along climatic and edaphic gradients were analyzed to improve the understanding of SOC dynamics in temperate grassland ecosystems. Materials and methods: Soil and plant samples were collected along climatic and edaphic gradients. Meteorological data were extracted from a regional climate database, which was spatially interpolated based on the records at 107 climatic stations located in Inner Mongolia. δ13C, carbon and nitrogen contents of soil and plant, soil pH, soil clay, silt, and sand contents were determined. Δδ13C and soil C:N were calculated. The integrative effects of these factors were further estimated using stepwise regression, redundancy analysis (RDA) and T value biplots. Results and discussion: As expected, soil δ13C was positively related to vegetation δ13C, and higher than the vegetation δ13C. Vegetation and soil δ13C and Δδ13C were all related to growing season precipitation (GSP) and growing season temperature (GST). However, when climatic and edaphic factors were considered together, vegetation δ13C was positively related to GST and soil C:N, soil δ13C was positively related only to GST, and Δδ13C was negatively related only to soil C:N. Unlike previous research conducted at the species level which only included C3 species, GST, instead of precipitation, was the dominant controlling factor of vegetation δ13C. Conclusions: GST influences vegetation δ13C mainly through its effect on relative abundance of C4 plants. Soil C:N rather than climatic factors is the dominant controlling factor of SOC decomposition, and the effects of climatic factors on SOC decomposition are indirect and induced by their effects on soil C:N through influencing species composition and plant C:N. Measuring vegetation δ13C, soil δ13C, and △δ13C simultaneously is necessary to comprehensively understand how environmental changes influence ecosystem carbon cycles. [ABSTRACT FROM AUTHOR]

Unraveling the distributions and controls of soil carbon (C) and nitrogen (N) accumulation is conducive to providing guidance for sustainable ecosystem management. Although the factors that affect soil C and N accumulation have been widely investigated, the relative importance of these factors and whether they confer direct or indirect effects remain unclear. Herein, we examined the distributions of soil organic carbon (SOC), soil inorganic carbon (SIC), and total nitrogen (TN) stocks across the 0–200 cm soil profiles in grasslands, forestlands, and shrublands on the Loess Plateau. Moreover, we determined the relative contributions of land use, topography, and soil properties (texture, water, phosphorus, and available nitrogen) to their variations. The results showed that with increasing soil depth, SOC and TN stocks decreased, while SIC stocks fluctuated. However, large amounts of SOC, SIC, and TN were stored in the deep soil layers (100–200 cm), with values of 3.06, 26.63, and 0.50 kg/m2, respectively. In the 0–200 cm soil layers, the total SIC stock was 53.40 kg/m2 and was 6.8 times higher than the total SOC stock. Among different plant communities, grasslands had the highest SIC stock (54.83 kg/m2), while Armeniaca sibirica and Robinia pseudoacacia had the highest SOC stock (10.06 kg/m2) and TN stock (1.49 kg/m2), respectively. Furthermore, approximately 85% of the variations in SOC, SIC, and TN stocks were jointly affected by land use, topography, and soil properties, in which soil properties acted as the most important driving factors, followed by topography and land use. In particular, topography affected SOC, SIC, and TN stocks mainly through its effects on soil texture and water. Overall, vegetation restoration scenarios incorporating grasslands and Robinia pseudoacacia are highly recommended and should be tailored according to specific topographic features. • SIC stock was 6.8 times higher than SOC stock in the 0–200 cm soil layers. • Grasslands performed better in soil C accumulation than forests and shrubs. • Land use, soil property, and topography explained 80% of the changes in C and N. • Land use played a less important role in affecting C and N than topography. • Topography affected soil C and N accumulation by influencing soil clay and water. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) plays an important role in soil biological activity and transport of pollutants and nutrients in soils, but very little information is available with regard to the long-term impact of agricultural management practices on the dynamics and fate of DOM in acidic soils. The seasonal and inter-annual variation of dissolved organic carbon (DOC) and nitrogen (DON) contents and leaching were investigated in an acidic clay soil (Ferric Acrisol) by a long-term field lysimeter experiment in subtropical China. The experiment was conducted from 2002 to 2010 with 4 fertilization treatments under maize monoculture: no manure (CK), low-rate manure with 150 kg N ha −1 y −1 (LM), high-rate manure with 600 kg N ha −1 y −1 (HM), and high-rate manure with 600 kg N ha −1 y −1 and lime at 3000 kg Ca(OH) 2 ha −1 3 y −1 (HML). Manure application resulted in a seasonal variation of soil DOC and DON, and significant effects were observed by manure DOC, microbial biomass and soil water content. Soil DOC, which was mainly determined by soil organic matter and soil water content, increased yearly until the seventh year when it was stabilized. Manure application on acidic clay soil did not alter DOC leaching, whereas DON leaching clearly increased after three years of high manure application of 600 kg N ha –1 y –1 . The average annual DON leaching losses under long-term manure application had a range of 3.8–5.4 kg ha –1 , accounting for 6–11% of total nitrogen leached. The addition of lime, combined with manure application, produced no impact on soil dynamics and leaching of DOC and DON, with the exception of increasing emission of CO 2 . [ABSTRACT FROM AUTHOR]

• C and N stocks in cropland following R. pseudoacacia afforestation were quantified by a national meta-analysis. • Afforestation with R. pseudoacacia on cropland generally increased C and N stocks. • Changes in C and N stocks varied with plantation attribute, climate, topography, soil. Afforestation made great contributions to ecological benefits across China. Robinia pseudoacacia is widely used in the Grain-for-Green Program. The responses of soil organic carbon (SOC) and soil total nitrogen (STN) to afforestation with R. pseudoacacia on cropland depend on plantation attributes, climatic factors, topographic features, and edaphic variables, thus making a synthesis of these studies necessary for understanding the magnitude and direction of SOC and STN to afforestation and the associated regulating factors. A meta-analysis was employed by compiling data of 1202 paired observations from 94 peer-reviewed publications to depict potential mechanisms of change in SOC and STN stocks following afforestation with R. pseudoacacia on cropland. Afforestation with R. pseudoacacia on cropland, on average, significantly and positively increased SOC and STN stocks. The changes in SOC and STN stocks increased with plantation age and altitude, but decreased with mean annual temperature, slope gradients, soil depth, soil clay content, initial SOC content and initial STN content. Greater accumulation rates of SOC and STN stocks after afforestation were detected in middle canopy density (0.6–0.8) and middle mean annual precipitation (450–550 mm). Among four kinds of biotic and abiotic factors, plantation attributes made greatest contributes to the variance in the response size of SOC and STN stocks. In particular, plantation age was the most essential variable on the response size of SOC and STN stocks. These results indicated that SOC and STN stocks following afforestation with R. pseudoacacia on cropland could be enhanced through plantation management practices. [ABSTRACT FROM AUTHOR]

• Controlling factors of organic carbon and nitrogen in alpine meadows were determined. • Grazing exclusion does not increase soil organic carbon and total nitrogen. • Soil organic carbon was explained by interaction between vegetation and soil. • Biomass, cover, soil moisture and clay were key factors affecting organic carbon. The accrual of soil organic carbon (SOC) and nitrogen (N) in grassland is an important management option to improve the ecosystem functions of grassland. However, how abiotic (such as grazing exclusion (GE)) and biotic factors influence SOC and N and their different fractions in Tibetan alpine meadows remains unclear. In this study, we evaluated the relative importance of abiotic and biotic factors that drive SOC and N contents in soil density fractions by performing redundancy analysis based on three long-term (10 years) fenced alpine meadows maintained in the permafrost region of the Tibetan Plateau in China. Biotic factors comprise plant aboveground biomass, cover and diversity, whereas abiotic factors include soil properties (i.e. soil moisture, pH, clay, silt, sand, total phosphorus, available phosphorus, microbial biomass carbon and N, available N, C:N ratio and C:P ratio) and GE. Site rather than GE has significant effects on the SOC and N contents. GE caused no increase in the SOC and N contents in the whole soil and fractions. Redundancy analysis showed that 96.7% of the variations in SOC and N fractions can be explained by the selected explanatory variables. Aboveground biomass, cover, soil moisture and clay contents were key factors that affected the SOC and N fractions. The SOC and N fractions were mainly explained by the interaction between vegetation and soil, followed by soil, vegetation and GE. The study highlighted the importance of considering the covariation of vegetation and soil for evaluating the SOC and N dynamics in alpine meadows. The effect of GE (such as 10 years) on the SOC and N contents in alpine meadows can be weak in the permafrost region of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

• SOC in the collapsing gully was significantly lower than that in the hillslope. • There was no organic carbon enrichment in the alluvial fan and check dam. • The loss of soil clay and iron oxides in collapsed soil intensified SOC erosion. • Collapsing gullies deteriorated soil properties and accelerated SOC loss. Collapsing gullies are one of the most serious soil erosion problems in the tropical and subtropical areas of South China. However, few studies have determined the effects of collapsing gullies on the redistribution and loss of soil organic carbon (SOC) in the red soil hilly region. This study investigated the variations in different kinds of SOC in a collapsing gully and a hillslope and the relationships between various soil properties and SOC. The results showed that the dissolved organic carbon (DOC), particulate organic carbon (POC), readily oxidizable organic carbon (ROOC) and total organic carbon (TOC) contents on the hillslope were higher than those in the collapsing gully. Below the location of upper catchment in the collapsing gully, the DOC, POC, ROOC and TOC contents were all greatly reduced, and there was no organic carbon enrichment in the alluvial fan and check dam. The stability of SOC in the collapsing gully was lower than that in the hillslope. The average free iron oxides (Fe d), organically bound iron oxides (Fe p) and clay contents in the collapsed soil were much lower than those on the hillslope. SOC content was significantly and positively correlated with the soil Fe d , Fe p and soil clay contents but negatively correlated with soil pH. Among these soil parameters, the dominant factors influencing TOC in the red soil hilly region were soil ROOC and soil pH. The SOC density of 0–30 cm soil in the collapsing gully was equivalent to nearly 15.9% of that in the hillslope. These results demonstrate that collapsing gullies have highly deteriorated soil properties and are therefore subject to accelerated SOC loss in the red soil hilly region. [ABSTRACT FROM AUTHOR]

• Current estimate of shrubland soil carbon density was higher than that for all Chinese terrestrial ecosystems. • Precipitation explained more variation of soil carbon than temperature. • Soil type was a key regulator of soil carbon. • Belowground biomass appears to provide the primary source of shrubland soil carbon. The soils of shrublands are important for organic carbon storage in terrestrial ecosystems, but geographical patterns and environmental controls of soil organic carbon (SOC) remain largely understudied compared to other terrestrial ecosystems, leaving a significant gap in our understanding of terrestrial ecosystem carbon budgets. Here, we quantified SOC density (SOCD) and its potential determinants based on a comprehensive dataset with a consistent stratified random sampling of extensive soil profiles down to the parent material or to one meter depth across 1211 sites across China. Our up-to-date estimate of SOCD in Chinese shrublands is an average of 8.36 kg m−2, and ca. 43% of SOC is stored in the upper 20 cm relative to the one meter top soil, which is higher than estimates for shrublands globally. We also observed that SOCD was positively related to shrubland biomass and more so with belowground biomass. Furthermore, SOCD was positively related to mean annual precipitation (MAP), soil total nitrogen (N), phosphorus (P), clay and silt percent, but decreased with increasing mean annual temperature (MAT). Dark felty soils stored the highest SOCD and frigid desert soils stored the lowest. Soil total nitrogen (N), MAP, soil type, MAT, and belowground biomass, soil clay, and pH were the best predictors of total SOCD in Chinese shrublands. We concluded that Chinese shrubland soils store the lowest density of organic carbon so far recorded compared to forests and grasslands, and that the vertical distribution of SOC in Chinese shrublands was much shallower. While both climate (in particular MAP) and soil total N exerted dominant control over geographical patterns of SOCD across Chinese shrublands, soil type also played a significant role. Our study also emphasizes this key role of edaphic variables in determining the SOCD of shrublands and that they should be better incorporated into large-scale assessments of SOC dynamics. Our study extends existing work conducted in forest and grasslands and provides the most up-to-date knowledge on benchmark values for SOCD in Chinese shrublands, with important implications for predicting the fate of C stored in shrubland soils in response to climate change. [ABSTRACT FROM AUTHOR]

Vegetation restoration affects the stability of soil organic carbon (SOC) by changing the composition of soil carbon pools, including active carbon (C a), the labile pool of SOC; slow carbon (C s), the physically stabilized pool of SOC; and resistant carbon (C r), the chemically stabilized pool of SOC. The aims of this study were to determine how SOC pools changed during restoration of a subtropical forest and to what extent vegetation characteristics and soil properties affected the changes in SOC pools. Soil samples were collected to 40 cm in four plant communities along a restoration chronosequence: scrub-grassland (4–5 years), shrubs (10–12 years), coniferous and broadleaved mixed forest (45–46 years), and evergreen broadleaved forest (90–91 years). Laboratory incubations were used to measure CO 2 production during SOC mineralization, and acid hydrolysis was used to measure C r. The CO 2 production and C r data were fitted to a three-component first-order kinetic model to determine the C a and C s. Pearson's correlations, stepwise multiple line regressions, and variation partitioning analysis were used to determine the key factors that affected SOC pools. The results showed that vegetation restoration increased the contents of SOC from 1.67 to 47.6 g kg−1, C a from 0.03 to 0.35 g kg−1, C s from 1.32 to 24.5 g kg−1, and C r from 0.33 to 22.8 g kg−1. During vegetation restoration, the increase in SOC was primarily due to carbon (C) stored in stable pools (i.e., C s or C r), and the portion of C r in total SOC increased markedly from 18.5 to 56.3%. Fine root biomass was the primary driver that controlled SOC pools during vegetation restoration. The C/N ratio of litter had a greater effect on C a and C s than that of other factors, whereas the soil clay content contributed secondarily to C r. The results suggest that vegetation restoration increases not only the amounts of SOC, C a , C s , and C r but also the stability of the SOC pool in subtropical soil. The relatively rapid increases in C s and C r following vegetation restoration played a crucial role in C sequestration. Therefore, strong measures to preserve natural forests and facilitate vegetation restoration should be the primary approach to increase long-term soil C sequestration in this region. • Soil organic carbon (SOC) content increased as vegetation restoration proceeded. • The increased SOC was mainly stored in the more stable carbon (C) pools. • Rapid increases in resistant C to SOC ratio played a crucial role in C stabilization. • Fine root biomass was the primary driver of the increased SOC pools with restoration. [ABSTRACT FROM AUTHOR]