Aims Vegetation restoration plays an important role in the accumulation and storage of soil organic carbon (SOC). Our objectives were to investigate the effects of vegetation restoration on SOC and to explain the underlying mechanisms of carbon sequestration during vegetation restoration in the mid-subtropical China.
Methods According to the disturbance intensity and the degree of restoration, we used the space-for-time substitution method by selecting four different types of vegetation communities, composed of Loropetalum chinense-Vaccinium bracteatum-Rhododendron simsii scrub-grass-land (LVR), Loropetalum chinense-Cunninghamia lanceolata-Quercus fabri shrubbery (LCQ), Pinus massoniana-Lithocarpus glaber-Loropetalum chinense coniferous-broad leaved mixed forest (PLL), and Lithocarpus glaber-Cleyera japonica-Cyclobalanopsis glauca evergreen broad-leaved forest (LAG) to represent the successional sequence in the secondary forests in Changsha County, Hunan Province, China. Permanent plots were established in each vegetation communities. Soil samples (0-40 cm) were collected and divided into four layers (0-10, 10-20, 20-30 and 30-40 cm). Soil organic carbon concentration (CSOC) and soil organic carbon density (DSOC) were measured. The main influencing factors on CSOC and DSOC were analyzed with Principal Component Analysis and Stepwise Regressions Analysis.
Important findings 1) Along vegetation restoration, CSOC and DSOC increased dramatically. The CSOC was the highest in LAG, which was 12.5, 9.3 and 4.7 g·kg -1 higher than in LVR, LCQ and PLL in 0-40 cm soil depth, increasing by 248.5%, 113.1% and 58.5%, respectively. The increments of DSOC in LAG at 0-40 cm soil depth were 67.1, 46.1 and 32.5 t C·hm -2, and increased by 182.0%, 79.7% and 45.6% compared to DSOC in LVR, LCQ and PLL, respectively. 2) Correlation analysis showed that CSOC and DSOC were strongly and positively correlated with species diversity index, community total biomass, aboveground biomass, root biomass, existing biomass in litter layer, nitrogen (N), phosphorus (P) concentration in litter layer, soil total P, soil available P, soil C/N ratio (except CSOC), soil C/P ratio, soil N/P ratio and percentage of soil clay (< 0.002 mm), but significantly and negatively correlated with C/N in litter layer (except DSOC), C/P in litter layer, soil pH and soil bulk density, suggesting that the differences in CSOC and DSOC under different vegetation stages were related to both vegetation and soil properties. 3) The results of principal component analysis and stepwise regression analysis revealed that soil C/P, pH, concentration of soil clay (except CSOC) and C/P in litter layer were the dominant factors affecting CSOC and DSOC during vegetation restoration. Among them, soil C/P ratio ranked first. These results indicated that the differences in soil C/P ratio, pH, soil clay concentration and C/P in litter layer were responsible for the changes in SOC during vegetation restoration.