Increases in bacterial community network complexity induced by biochar-based fertilizer amendments to karst calcareous soil

Karst ecosystems are vulnerable to degradation and constitute a significant proportion of southwestern China. Here, we explored the amendment of karst soils with biochar in combination with swine manure compost and chemical fertilizer with the aim of improving the microbial community structure and soil nutrient status of these soils. A pot experiment with eight treatments including CK, F, M, MF, B, BF, BM and BMF were set up, where CK was the control, F was chemical fertilizer, M was swine manure compost, and B was wood-derived biochar. The results showed that biochar and biochar-based fertilizer treatments (B, BF, BM and BMF) had higher bacterial diversity (Simpson and Shannon), microbial biomass and soil nutrient content compared to the corresponding no-biochar treatments (CK, F, M, MF), and treatments with compost (M, MF, BM and BMF) had higher values than no-compost treatments (CK, F, B and BF). The cluster and LEfSe analyses showed that different treatments had distinct bacterial community structure and composition; the biochar network (B, BF, BM and BMF) had a higher number of nodes, links and modules than the no-biochar network (CK, F, M and MF), and the compost network (M, MF, BM and BMF) had more complexity than the no-compost network (CK, F, B and BF). Soil variables significantly influenced the biochar and the no-biochar networks, whereas there was no significant correlation with compost or no-compost networks. In conclusion, additions of both biochar and organic compost induced microbial correlation network complexity increases and improved the soil nutrients, indicating biocharbased fertilizer had great benefits on restoration of karst degraded soil.