Enhanced soil quality after forest conversion to vegetable cropland and tea plantation has contrasting effects on soil microbial structure and functions

Land-use changes could potentially exert a strong influence on soil quality and soil microbial communities. Moreover, microbial taxa are also important drivers of soil ecological functions. However, the linkage between soil quality and soil microbial communities is in need of deeper understanding. In this study, we examined the effects of soil quality on microbial community structure and functions after forest conversion to vegetable cropland and tea plantations. Soil quality index was significantly increased after natural forest conversion to vegetable cropland and tea plantations. Soil bacterial beta diversity significantly correlated to soil quality, but the sensitivity of individual microbial groups varied in response to changes in soil quality. Higher soil quality promoted bacterial diversity in vegetable cropland but decreased it in tea plantations, which implied soil quality was a structural factor in bacterial community composition but had contrasting effects for croplands versus plantations. Agricultural management played a negative role in maintaining microbial interactions, as identified by the network analysis, and furthermore the analysis revealed key functions of the microbial communities. After land-use change, the abundance (e.g., level, intensity) of microbial N-cycling function increased in tea plantations but decreased in vegetable cropland. The abundance of C-cycling function featured an opposite trend. Higher level of N-fixation in tea plantations but the higher abundance of N-oxidation in vegetable cropland was demonstrated. Higher abundance of ammonia-oxidizing bacteria and ammonia-oxidizing archaea as identified by qPCR in vegetable cropland corroborated the FAPROTAX function prediction. Therefore, the key taxa of soil microbial communities and microbial functions were largely dependent on changes in soil quality and determined responses to specific agricultural management.