Long-term silicate fertilization increases the abundance of Actinobacterial population in paddy soils

Silicon (Si) is widely used in improving crop yield, but effect of its application on soil bacterial community composition is poorly known. Quantitative PCR and high-throughput sequencing targeting the bacterial 16S rRNA gene were employed to characterize the bacterial community composition of long-term fertilized paddy soils treated with nitrogen (N), phosphorus (P), potassium (K), and Si (NPK + Si), with NPK or not fertilized (control). The NPK + Si fertilization significantly increased the urease and dehydrogenase activity. The relative abundance of Actinobacteria was significantly higher in the NPK + Si soil than in other two soils. Linear discriminant analysis (LDA) and effect size (LEfSe) analysis demonstrated that Actinobacteria and its associated taxonomic groups were significantly more abundant in the NPK + Si-treated plots. The bacterial community composition of the NPK + Si soil was significantly different from those of NPK and control soils as shown by the ordination plot. According to distance-based regression analysis, variation in bacterial community composition was related to available SiO2 and P2O5 concentrations. Functional profiles predicted from 16S rRNA abundance data showed that the NPK + Si plots were more enriched by genes coding enzymes related to plant growth promotion compared to NPK and control plots.