Long-term agronomic practices alter the composition of asymbiotic diazotrophic bacterial community and their nitrogen fixation genes in an acidic red soil

Abstract

The asymbiotic diazotrophic bacteria are important for nitrogen (N) input to soil. Here, we investigated asymbiotic diazotrophic bacteria in an acidic red soil from functional, phylogenetic, and ecological perspectives. We firstly confirmed that phosphorus (P) availability determines the overall asymbiotic N fixation potential in the red soil. Then, we analyzed the soil bacterial community and N fixing (nifH) gene composition. Long-term different fertilizations significantly affected the composition of soil bacterial community. In addition, long-term organic cultivations increased most of the asymbiotic diazotrophic bacteria and the corresponding nifH gene abundances. Few asymbiotic diazotrophic bacteria, belonging to Chloroflexaceae, Methylocystaceae, Enterobacteriaceae, and Pseudomonadaceae, and their corresponding nifH genes were more abundant in N and P co-limited than in not co-limited soils, suggesting that some bacterial taxa from these families might be activated under nutrient limited conditions. Our findings provided new information for the distribution of asymbiotic diazotrophic bacteria in red soil and gave insights into the ecology of diazotrophic bacteria.