Divergent modulation of land use-driven changes in soil properties and herbicide acetochlor application on soil nitrogen cycling

To boost grain yield, land use conversion and herbicide application are commonly considered two primary anthropogenic interventions to microbe-mediated nitrogen (N) cycling of soils. However, the coupling effects of land use and herbicide acetochlor application on soil N cycle are still poorly understood although separate role had been extensively investigated. A 31-day laboratory batch experiment on bacterial communities associated with N metabolism in soil collected from various land use types were carried out under acetochlor application using classic dilution plating method. The results showed soil characteristic changes induced by land-use strongly influenced soil bacterial communities, and pH, nitrate (NO3−-N) contents were the best predictors for nitrifying bacteria (p < 0.05). Soil nitrifying bacteria was the dominant species in vegetable fields (VF30 and VF70), whereas denitrifying bacteria was the keystone species in paddy field cultivated over 100 years (PF100), resulting in mean nitrification potentials of vegetable fields approximately 3 times that of PF100 (p < 0.05). Rather, a dosage of 10 mg kg–1 acetochlor application inhibited denitrification potentials in all three soils (p < 0.05), and had negligible impact on nitrification potentials. This could be attributed to decreases in abundance and activity of denitrifying bacteria after acetochlor application. Therefore, acetochlor application was capable of decreasing denitrification of N removal from soils to atmosphere, and vegetable cultivation enhanced transformation of ammonium (NH4+-N) to NO3−-N species in comparison to paddy field. Our findings renew functional differentiations of land use and herbicide acetochlor application on soil N cycling, and give insight for soil N nutrient management in agricultural practices to ensure food security and improve environmental sustainablility.