Roles of soil bacteria and fungi in controlling the availability of nitrogen from cover crop residues during the microbial hot moments

Abstract Nitrogen (N) mineralization, the conversion of organic N into inorganic N, plant available N, is a microbe-mediated processes. However, the roles that specific microbial taxa play in the release of N from cover crop residues during the residual decomposition have been understudied. Pot-based experiments were established in soils incorporated with rye, hairy vetch (HV), and rye+HV cover crop residues. We used DNA-based molecular approaches to quantify and identify bacteria and fungi under each cover crop. Correlation analysis was used to evaluate the roles of specific microbial taxa (i.e., the dominant, influenced, and keystone taxa). Fungal DNA in all cover crop-treated soils peaked within 5–25 days following residue incorporation, which was also the critical period for N mineralization. Additionally, positive links occupied the correlation networks within and between bacteria and fungi in all treatments, suggesting that the microbes synergistically cooperated to degrade the residues and mineralize N. The abundance of decomposers (e.g., Cytophagaceae and Sinobacteraceae) was promoted by HV and rye+HV inputs due to residue lability. The dominant (e.g., Mortierellaceae, Hypomicrobiaceae, and Aspergillaceae), influenced (i.e., Actinosynnemataceae, unidentified SAR202, and Parachlamydiaceae), and keystone (e.g., Clostridiaceae, Cystofilobasidiaceae, and Dolo 23) taxa were positively or negatively correlated with N availability indicators (i.e., soil inorganic N, β-glucosidase enzyme activity, and soil microbial biomass) in each cover crop-treated soil. The results indicate that the taxa were principally responsible for N mineralization from each cover crop input during the residual decomposition period.