Effect of microbial inoculation on nitrogen transformation, nitrogen functional genes, and bacterial community during cotton straw composting

The effects of microbial agents on nitrogen (N) conversion during cotton straw composting remains unclear. In this study, inoculation increased the germination index and total nitrogen (TN) by 24–29 % and 7–10 g/kg, respectively. Inoculation enhanced the abundance of nifH, glnA, and amoA and reduced that of major denitrification genes (nirK, narG, and nirS). Inoculation not only produced high differences in the assembly process and strong community replacement but also weakened environmental constraints. Partial least squares path modelling demonstrated that enzyme activity and bacterial community were the main driving factors influencing TN. In addition, network analysis and the random forest model showed distinct changing patterns of bacterial communities after inoculation and identified keystone microorganisms in maintaining network complexity and synergy, as well as system function to promote nitrogen preservation. Findings provide a novel perspective on high-quality resource recovery of agricultural waste.