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[Display omitted] • SOC storage and stability increased with vegetation restoration and succession. • Macroaggregates play an important role in SOC storage and stability. • Coniferous forests are more conducive to soil carbon fixation. Soil organic carbon (SOC) plays the most significant role in climate change mitigation and ecosystem productivity. However, dynamic changes in the storage and stability of SOC during vegetation restoration and succession, especially the physical protection role of soil aggregates, are not well understood. This study, therefore, explored the variations in SOC storage and stability along with vegetation restoration by combining the physical protection of soil aggregates with the chemical structural stability of organic carbon (OC). OC fractions and carbon functional groups of bulk soil and soil aggregates were investigated using soil samples collected from abandoned farmland, grassland, miscellaneous shrubland, pioneer arbor forest, and coniferous forest plots representing typical vegetation restoration consequence on the Loess Plateau of China. Vegetation restoration enhanced clumps of clay particles with visible pores and cementing substances. The contents of OC fractions (total, inert, and active carbons) in bulk soil and aggregates significantly increased during vegetation restoration process. Total and active OC in macroaggregates (>0.25 mm) were significantly higher than those in other aggregate fractions, while inert OC had no significant difference among different aggregate fractions. The elevated absorption intensity, i.e., absolute content of OC functional groups, especially stable OC functional groups, enhanced SOC chemical stability during vegetation restoration. From the abandoned farmland to miscellaneous shrubland, the relative content of active OC functional groups significantly increased and was primarily distributed in macroaggregates (84.94–86.32%), while silt–clay aggregates (<0.053 mm) had higher relative content of stable functional groups (21.84–26.53%). A significant increase was observed in the relative content of the stable functional group from miscellaneous shrubland to pioneer arbor forest, primarily in silt–clay aggregates (∼27.15%). In the coniferous forest, stable functional groups mainly distributed in macroaggregates also showed the most pronounced increase (∼36.15%). We concluded that vegetation restoration improves the soil structure and storage and stability of SOC due to the increased accumulation of OC in macroaggregates and enhanced chemical stability of OC in silt–clay aggregates from the abandoned farmland to the pioneer arbor forest. However, SOC stability in the coniferous forest is significantly influenced by macroaggregates in the soil. [ABSTRACT FROM AUTHOR]

[Display omitted] • SOC stocks of VCEs were estimated and projected at a 10 m spatial resolution. • Climate and soil salinity are critical for estimating SOC stocks in the VCEs. • Warming would decrease SOC stocks of VCEs by enhancing SOC decomposition. • Increasing precipitation would increase SOC stocks by reducing soil salinity. • SOC stocks of VCEs in the Bohai Rim could reduce ∼ 12 % − 19 % between 2041 and 2100. Vegetated coastal ecosystems (VCEs) have much higher organic carbon sequestration rates and storage capacities than most other earth surface ecosystems, and thus play a vital role in blue carbon sequestration for climate change mitigation. However, soil organic carbon (SOC) stock assessment in VCEs at a large regional-scale remain problematic, and the controlling mechanisms for SOC remain poorly understood. Here, we estimated current and future SOC stocks of VCEs in the Bohai Rim Region, China at a spatial resolution of 10 m, using a data-driven method based on multi-source data; and investigated the key environmental and anthropogenic controls. The total SOC stocks and SOC density of VCEs in the Bohai Rim Region were estimated to be approximately 62.7 Tg carbon and about 68.8 Mg ha−1, respectively (in the upper 1 m of soil). We found that climate and soil salinity are the most critical environmental controls of SOC stocks within VCEs in the region. Increasing temperature and soil salinity would increase SOC decomposition and decrease plant productivity, resulting in a decrease in SOC stocks. Conversely, increasing precipitation would increase SOC stocks by reducing soil salinity. We projected that the potential losses of SOC stocks due to the combined effects of climate changes, sea-level rise, and anthropogenic disturbances would be ∼ 12.2 % between 2041 and 2060 under two Shared Socioeconomic Pathway (SSP) scenarios (SSP245 and SSP585), extending to 19.3 % between 2081 and 2100. The decreases in SOC stocks would occur mainly in the higher latitude and colder regions. The study demonstrated the potential significant reduction in SOC stocks in coastal ecosystems and provided an important framework for better understanding the blue carbon ecosystems. [ABSTRACT FROM AUTHOR]

• Tree species diversity decreased standing biomass C stock via the dominant tree biomass C stock. • Tree species diversity enhanced the C and N stocks in stand litter mainly via affecting the proportion of conifer. • Tree species diversity enhanced the soil organic C and N stocks via increasing their stable factions. • Tree species diversity can elevate the stabilities of soil organic C and N stocks in the secondary forests. Carbon (C) and nitrogen (N) stocks are important for food security and mitigation of climate change, also could be likely affected by tree diversity. However, a detailed evaluation of the relationships between tree species diversity and stand biomass C (AGC), and the C and N stocks of stand litter and soil is still scant, especially in secondary forests. Thus, we assessed the associations between tree species diversity (i.e., Shannon-Wiener index) and the AGC stock, the C and N stocks in stand litter and soil [soil organic carbon (SOC), N, microbial biomass fractions (MBC and MBN), heavy fractions (HFOC and HFON) and mineral associated factions (MAOC and MAON)] at the plot level (25 m × 25 m) in mature secondary forests in subtropical China. We also used the structural equation model (SEM) to explore the underlying mechnism by which tree diversity drives the AGC stock and the C and N stocks in stand litter and soil. We found that the tree species diversity decreased AGC stock via the dominant tree biomass C stock. However, the tree species diversity enhanced the C and N stocks in stand litter mainly via affecting conifer proportion, and the SOC and N stocks at the depth of 0–40 cm via increasing their stable factions (i.e., heavy fractions and mineral associated factions). We also observed the tree species diversity had positive effects on the stocks of MBC, HFOC and HFON in soil epipedon, and had non-significant effects on the stocks of MBN, MAOC and MAON. Our results revealed that tree species diversity can elevate the soil C and N stocks and their stability in the subtropical secondary forests of China. [ABSTRACT FROM AUTHOR]

[Display omitted] • The greening rate increased with time after cascade-dam implementation. • Temperature was the most significant driving force on vegetation growth. • Temperature and sunshine hours positively affected vegetation. • Vegetation was negatively correlated with precipitation and vapor pressure deficit. The eco-environment in ecologically fragile regions has received increasing concern due to its vulnerability to climate changes. Determination of vegetation dynamics is a prerequisite for sustainable management of eco-environment evolution due to its vital role in regulating earth system and ecosystem services. China′s Three Gorges Reservoir area (TGRA), as a typical ecologically fragile region, was selected to explore its vegetation dynamics and response to local climate in different periods (1982–2020) of GZD-TGD (Gezhou Dam-Three Gorges Dam). The 1982–2020 NDVI dataset was obtained by integrating the overlapping period (2001–2015) of GIMMS NDVI and MODIS NDVI. The results demonstrated that TGRA exhibited a generally greening trend in 1982–2020, and the greening rate increased with the implementation of GZD-TGD, particularly in the last 20 years, which greatly promotes the capacity of vegetation carbon sink. At the annual scale, the mitigation of climate warming occurred with GZD-TGD implementation, particularly after the first impoundment of TGD (−0.0114 ℃yr−1). At the seasonal scale, a certain cooling effect in summer and a warming effect in other seasons (especially in winter) induced by this cascade project were observed, which became more pronounced after the water level reached 175 m. Furthermore, temperature had the most significant positive effect on vegetation dynamics, which increased with GZD-TGD implementation. The driving force of precipitation, VPD (vapor pressure deficit) and sunshine hours was relatively less significant but could not be ignored, with negative contributions from precipitation and VPD and positive contribution from sunshine hours. These findings provide further insights into the effect of climate changes mediated by GZD-TGD on vegetation growth and facilitate the dissection of the complex soil–plant-atmosphere feedback interaction. [ABSTRACT FROM AUTHOR]

• The SOC content in macroaggregates was 8–67% higher than that in other aggregates. • Hydrolase activities were positively correlated with the SOC content in aggregates. • Microbial community diversity decreased as the soil aggregate size increased. • Forty-year-old orchards primarily promoted SOC storage in macroaggregates. Soil organic carbon (SOC) is closely related to ecosystem functions and services, such as biodiversity conservation and the mitigation of climate change. Soil aggregates are among of the most important microbial hotspots and are an important material for C cycling. However, the effects of microbial properties such as enzyme activities and microbial communities on SOC across different soil aggregates remains unclear. Here, we evaluated the SOC, microbial biomass carbon (MBC) content, hydrolase enzyme activities (i.e., β-glucosidase, α-glucosidase, and sucrase), and microbial communities in different soil aggregates in 7-, 20- and 40-years orchards and newly established orchards in southern China to determine the relationships between the SOC and microbial properties. The aggregate-associated SOC, MBC contents and three enzyme activities were unevenly distributed. The average SOC and MBC contents in > 0.25 mm aggregates increased by 40% and 26%, respectively, compared with those in the other aggregates (< 0.25 mm). The β-glucosidase and α-glucosidase activities in the 0.053–0.25 mm aggregates were the lowest among different aggregates, but the sucrase activities did not differ significantly across soil aggregates of different sizes. The average SOC and MBC contents, and the three enzyme activities in the > 0.25 mm aggregates in the forty-year orchard increased by 2.53-, 1.41- and 2.09-fold, respectively, compared to those in the newly established orchard. Positive correlations with the soil aggregate size were observed for Chloroflexi, and negative correlations were found for Actinobacteriota, Proteobacteria and Acidobacteria. The relative abundance of Ascomycota increased, and the relative abundance of Basidiomycota decreased with increasing orchard age. Our study demonstrated that the increased orchard age (40 years old) accelerated C cycling in soil aggregates of different sizes by increasing aggregate-associated enzyme activities and changing the microbial community composition, and greater SOC accumulation occurred in macroaggregates (> 0.25 mm) than in microaggregates (< 0.25 mm). [ABSTRACT FROM AUTHOR]