Effects of biochar-based fertilizer on soil bacterial network structure in a karst mountainous area

The karst ecosystem is prone to degradation and accounts for a large proportion of land surface in southwestern China. In order to improve the nutrient status and microbial community structure of karst soils for the restoration of vegetation, we tested a management strategy of combining biochar, compost and chemical fertilizer to amend karst soil. With CK as the control, M as manure compost, B as wood biochar, and F as chemical fertilizer, field trials were set up with eight treatments (CK, M, F, B, M + F, B + M, B + F, and B + M + F). Our results showed that the biochar treatments had higher bacterial diversity and soil nutrient content than no-biochar treatments, and the compost treatments had higher bacterial diversity and soil nutrient content than no-compost treatments. Cluster and LEfSe analyses indicated that the structure and composition of bacterial community varied with different treatments; the compost network (M, MF, BM and BMF) had a higher number of nodes, links and modules than the no-compost network (CK, F, B and BF), and the biochar network (B, BF, BM and BMF) was more complex than the no-biochar network (CK, F, M and MF). Soil properties (soil organic carbon, available nitrogen, available phosphorus) were significantly correlated with soil bacterial networks. The addition of both organic compost and biochar enlarged the complexity of microbial-related networks and enhanced the soil nutrient status, indicating that biochar-based fertilizer was effective for soil restoration in degraded karst landscape.