Stoichiometric imbalance of soil carbon and nutrients drives microbial community structure under long-term fertilization

Fertilization affects soil microbial community by altering soil organic carbon (C) and nutrients availability. However, it remains unclear how changes in stoichiometric C, N, and P ratios resulting from fertilization affect microbial community. We investigated a 26-year field experiment receiving inorganic fertilizers (N, NP, PK, and NPK), organic N combination (with manure and straw), natural recovery (fallow), and no fertilizer (control). The aim of this study was to explore the responses of microbial community to C: N:P stoichiometry in soil and microbial biomass of topsoil (0–20 cm) and subsoil (20–40 cm). Results showed that compared to control treatment, organic application increased the ratio of fungi to bacteria (F:B) in topsoil and gram-negative bacteria to gram-positive bacteria (G−:G+) in subsoil. However, application of inorganic decreased both the F: B and G−:G+ ratio in topsoil. Increasing soil C, N and P availability resulted from inorganic fertilizers and organic combination fertilization caused stoichiometric imbalance between soil and microbial biomass. As a result, the F:B and G−:G+ ratio were positively related to C:N imbalance but negatively associated with N:P imbalance in topsoil. Redundancy analysis (RDA) showed that main factors regulating microbial community were pH, C:P and N:P imbalances in topsoil, whereas TDN, N:P imbalance, DOC and soil C:N in subsoil. Furthermore, C:P and N:P imbalance explained 16.4% in topsoil, and N:P imbalance explained 22.0% in subsoil of microbial community variation. These results reveal the shifts of soil microbial community are driven by changes in soil pH and C, N and P stoichiometric imbalance from long-term fertilization.