Responses of soil microbial communities to vegetation restoration on the Loess Plateau of China: A meta-analysis

Vegetation restoration has been implemented to prevent ecosystem degradation worldwide. However, the general response of soil microbial communities to vegetation restoration remains highly controversial. Herein, 417 paired observations from 74 studies on the Loess Plateau of China were selected to investigate the effects of vegetation restoration on the soil microbial community and to determine the factors that affected their variation. The results showed that vegetation restoration significantly increased microbial biomass (phospholipid fatty acid and microbial biomass C, N, and P) and enzyme activities (invertase, urease, phosphatase, catalase and glucosidase) but decreased the fungi to bacteria ratio (F:B). Specifically, microbial biomass was mainly affected by slope gradient, pH, and available nitrogen. Enzyme activities were mainly affected by available nitrogen, pH, and soil water content. F:B was mainly affected by available phosphorus. However, the variations in Oligotroph:Copiotroph ratio, gram-positive bacteria to gram-negative bacteria ratio, microbial diversity (Shannon index and OTU richness), and microbial activity (microbial respiration, metabolic quotient, and microbial entropy carbon) were nonsignificant. Our study also showed that the effects of vegetation restoration on the soil microbial community were substantially dependent on vegetation type (restoration type, leaf form, mycorrhizal type) and restoration year. For example, greater microbial biomass was found in soils of trees (sites that had been restored to forest), higher enzyme activity was found in soils of broadleaf tree species, and a lower F:B was found in soils of arbuscular mycorrhizal species.