The restoration age of Robinia pseudoacacia plantation impacts soil microbial biomass and microbial community structure in the Loess Plateau

Black locust (Robinia pseudoacacia, RP) has been widely grown for soil and water conservation in erosion regions. However, the effect on soil microbial profiles after long-term implementation of vegetation plantation was still unclear. In this study, soil samples from RP plantations of 10-, 15-, 30- and 38-year-old in a typical vegetation-recovering region on the Chinese Loess Plateau were investigated for microbial biomass carbon (MBC), nitrogen (MBN), phosphorous (MBP) and microbial community-profiles (revealed by phospholipid fatty acids, PLFAs). The results showed SOC, total N, MBC and MBP were significant (P < 0.05) higher in the older RP (30- and 38-year-old) than those in other younger plantations (10 and 15-year-old). Total viable microbial biomass (indicated by total PLFAs), bacterial PLFAs and MBP increased significantly (P < 0.05) with increasing plantation age. Soil microbial communities were distinctly differed in soils of younger- than in older- plantation plots. Redundancy analysis showed that the sampling site with various RP plantations (P < 0.05) was the most important factors in structuring various soil microbial communities. Soil C:N ratio, MBP and available P were also significant factors affecting soil microbial communities. These findings indicate that RP plantation has the potential to transform soil microbial biomass and microbial communities in the direction of improving soil P content in loess soil.