Effects of artificial restoration on vertical distribution of soil carbon storage following revegetation in a semiarid grassland of North China

Artificial restoration is an important strategy to restore plant communities and soil nutrients in degraded grassland ecosystems. Despite that research has been extensive on the impacts of vegetation restoration on soil carbon storage, little work has been tried to examine the impacts of artificial restoration on the vertical distribution of soil organic carbon (SOC) storage following revegetation in grassland ecosystems. In this paper, the responses of plant species diversity, litter biomass (LB), aboveground biomass (AGB), the relative biomass of three dominant plant species, and the belowground biomass (BGB) were quantified under five different restoration regimes (natural recovery, harrowing, harrowing plus fertilization, harrowing plus irrigation, harrowing plus fertilization and irrigation), to explore the direct and indirect effects of artificial restoration, mediated by changes in the plant properties following revegetation, on SOC storage in Leymus chinensis steppe, North China. We found that artificial restoration greatly facilitated the recovery of Leymus chinensis but lowered the plant diversity. Irrigation treatment, particularly harrowing plus irrigation, was associated with both higher BGB and LB, which had positive effects on SOC storage at the 30-60 cm soil layer when compared with natural restoration. In addition, artificial restoration had positive but not significant effects on SOC storage in the surface soil layer (0-10 cm) mediated directly by changes in BGB, while it exerted negative indirect effects on SOC storage at the 10-30 cm soil layer through low level of plant species diversity. The loss of two dominant species (Stipa krylovii and Cleistogenes squarrosa) could greatly impact SOC storage not only due to lowered species diversity but also the reduced quality of litter input into soil. It is therefore proposed that maintaining high levels of plant species diversity could help sustain higher soil carbon storage through producing high-quality root and litter. Our findings from the 9-year restoration experiment suggested that natural restoration is a sustainable grassland restoration regime to conserve both plant diversity and soil nutrients over short timescales in semi-arid grasslands in North China. In the long term, SOC storage can be substantially enhanced by artificial restoration, especially under treatments that include irrigation.