Forests have a higher soil C sequestration benefit due to lower C mineralization efficiency: Evidence from the central loess plateau case

Soil carbon (C) mineralization varies with vegetation restoration and plays an essential role in the soil C cycle. However, the response of soil C mineralization to different vegetation restoration types remains unclear. In this study, three vegetation restoration types for the restoration of cropland, namely forestland (Robinia pseudoacacia), shrubland (Caragana korshinskii), and grassland (Artemisia sacrorum and Stipa bungeana), were selected to determine how vegetation restoration types affect soil C mineralization. The vegetation in the assessed areas had been restored 20 years before this study. The results showed that vegetation restoration significantly increased soil CO2 efflux, whereas soil C mineralization efficiency (CME) decreased after cropland conversion. The lowest soil CO2 efflux and CME were observed in forestland, with the highest stable soil organic carbon (SOC) pool. Vegetation restoration significantly increased SOC and its C fraction stocks, and the variation in soil C fractions was regulated by vegetation restoration type. Soil microbial biomass carbon (MBC) and dissolved organic carbon (DOC) effectively reflected the variation in soil C mineralization and stability of the SOC pool, respectively. Soil CO2 efflux was controlled by litter biomass, macroaggregates, particulate organic C, MBC, and DOC, whereas CME was mainly influenced by aboveground biomass, pH, silt and clay content, macroaggregates and DOC. The study suggested that forestland should be selected as the preferred vegetation restoration type in the central Loess Plateau owing to its lower CME with similar C stocks.