Microbial succession and nitrogen cycle dynamics in agricultural soil under stress from the chiral pesticide cis-epoxiconazole

The nitrogen cycle is a vital component of the biogeochemical processes in agricultural soils, largely driven by often-overlooked microorganisms. The chiral pesticide cis -epoxiconazole stresses agricultural soils, but its stereoselective effects on nitrogen-cycle microbes are poorly understood. In a long-term soil incubation experiment, cis -epoxiconazole monomers reshaped microbial community composition and structure, impacted enzyme activity and functional genes, thereby influencing nitrogen cycling. Specifically, (−)-EPO treatment enriched key nitrogen cycle hosts and increased activity of β -glucosidase and urease, facilitating ammonia oxidation, dissimilatory nitrate reduction to ammonium, nitrogen fixation, and ammonification. In contrast, (±)-EPO treatment increased the relative abundance of denitrification functional microorganisms (Gemmatimonadetes and Proteobacteria) and genes ( narG and napA ), promoting denitrification and decreasing nitrogen availability. Meanwhile, (+)-EPO treatment suppressed the enrichment of key genes including napA , nirK , nosZ , nirBD , and nifH , along with urease activity, resulting in significant nitrogen flow reduction within the soil. This study provides a comprehensive and systematic analysis of the effects of multiple concentrations of cis -epoxiconazole on the nitrogen cycle in agricultural soils. The findings highlight the risks associated with the disruption of nitrogen-cycling gene profiles and stress on microbial regulation under chiral pesticides' practical application conditions.