Plastic film mulching with nitrogen application activates rhizosphere microbial nitrification and dissimilatory nitrate reduction in the Loess Plateau

Plastic film mulching combined with nitrogen application is a prime chief strategy for enhancing maize yields in rain-fed agricultural areas. However, how the practice affects the productivity and functions of soil by altering nitrogen transformation mediated by rhizosphere microorganisms in the Loess Plateau, remains unclear. In this research, an 7-year field location experiment was conducted to ascertain the effects of plastic film mulching with nitrogen application (225 kg N ha−1) on the rhizosphere microbial nitrogen transformation in a rain-fed maize field on the Loess Plateau. Plastic film mulching with nitrogen application reduced the pH value and also increased the abundance of microorganisms (e.g., Nitrosospira, Halomonas) and genes (e.g., pmoB-amoB, hao, nirB, and nirD) during the vegetative stage. This promoted nitrification and dissimilatory nitrate reduction to ammonium, which increased the content of inorganic nitrogen in the rhizosphere. During the reproductive stages, plastic flim mulching reduced the relative abundance of aerobic bacteria (e.g., Skermanella, Sphingomonas), and the ratio of (nirK + nirS) / nosZ, which inhibited denitrification and dinitrogen oxide emission potential. Overall, our findings highlight the feedback mechanism of soil nitrogen transformation to plastic film mulching with nitrogen application in the Loess Plateau, providing valuable insights for manipulating specific microorganisms to regulate nitrogen transformation and promoting the sustainability of soil ecosystems.