Impacts of Acetochlor on Nitrogen-Cycling-Related Microbial Communities in Riparian Zone Soils

Abstract

The riparian zone has a proven ability to reduce agricultural nonpoint-source nitrogen pollution. However, prior studies have only assessed nitrification and denitrification and their influencing factors, such as hydrology, climate, vegetation, and soil physicochemical properties, and overlooked the role of pesticide accumulation, which is an important nonpoint-source anthropogenic pollutant. This study investigated the response of the soil microbial nitrogen cycle in riparian zones to 60 days of acetochlor (ACE) exposure at doses of 0.5, 2.5, and 5.0 mg/kg. The results showed that ACE inhibited the transformation of soil NH3-N, NO3−-N, and NO2−-N and also decreased potential nitrification and denitrification rates by affecting the respective enzyme activities and related microbial communities. Metagenomic sequencing revealed that the expression of functional genes associated with NO3−-N transformation processes, including denitrification, dissimilatory nitrate reduction to ammonium, and assimilatory nitrate reduction, declined the most. The recommended field dose (0.5 mg/kg) showed a slight effect on soil microbial nitrogen transformation and the related microbial communities, whereas doses 5 and 10 times the recommended dose were highly inhibitory. This is a novel study exploring the effects of ACE on the microbial nitrogen cycle in riparian soils, also suggesting that pesticide accumulation in riparian zones could affect the health of aquatic ecosystems.