Objective Soil microbial interactions are crucial in regulating soil nitrogen (N) transformation processes in agroecosystems. Revealing the influence of no-tillage (NT) on microbial interactions and their relationship with soil N storage, could improve our understanding of the microbial ecological mechanisms underlying NT enhanced N retention.

Method Based on a 10-year field experiment in a Mollisol of Northeast China, the long-term effects of NT were investigated, compared with conventional ridge tillage (CT), on soil N storage, microbial N-cycling potential, and bacterial interaction networks across the 0 - 60 cm soil profile.

Result Compared with CT, NT increased total N (TN) and mineral N storage in the 0 - 60 cm soil profile by 11.3% and 44.3%, respectively. The complexity of bacterial networks increased with soil depth up to the 10 - 20 cm layer and then declined. NT enhanced network complexity across all soil layers relative to CT. Keystone taxa mainly belonged to the phyla Acidobacteriota, Proteobacteria, Gemmatimonadota, Actinobacteriota and Nitrospirota. and their cumulative relative abundance increased with depth. NT regulated N cycling processes across soil layers differentially by modulating the relative abundance of keystone species, thereby enhancing soil N accumulation and availability. In the 0 - 20 cm soil layer, NT increased the relative abundance of keystone taxa, potentially suppressing mineralization and promoting the accumulation of organic N. In the 20 - 60 cm soil layer, NT reduced the abundance of keystone species, which may weaken nitrification and denitrification potentials, thereby facilitating the accumulation of mineral N.

Conclusion Long-term NT improves soil N storage by regulating bacterial interaction networks and the functions of keystone taxa across soil depths, thereby optimizing microbial-mediated N transformation in agricultural soils.