New insights into cadmium-modulated relationships of phosphorus-nitrogen functions under herbicide disturbance in cornfields

Metallic micronutrients probably mediate the nutrient functions in soils with long-term herbicide application. However, will hazardous metal cadmium have a synergistic effect with herbicides, which amplifies the interference on soil nitrogen and phosphorus cycling functions? This study conducted a nationwide investigation to characterize the accumulation patterns of two typical herbicides (atrazine and nicosulfuron), cadmium, and metal micronutrients (iron, manganese, copper, and zinc) in maize fields. It specifically elucidated the individual disruptive effects of herbicides, the interaction mechanisms between herbicides and metals (particularly cadmium), and the key pathways and drivers influencing soil nitrogen-phosphorus functional linkages. Results showed that nicosulfuron and atrazine residues were negatively correlated with nitrogen and phosphorus functional genes, while the cadmium content was positively correlated with these functional gene abundance. Additionally, cadmium acted antagonistically with atrazine in terms of nutrient cycling functions. This is further verified by the higher sensitivity values of functional genes in the north than those in the south. Moreover, the results of the structural equation model showed that the abundance of nirK and nirS genes was significantly correlated with the abundance of the phoC gene in maize fields and herbicides, cadmium, iron, and zinc affected the phoC gene by affecting the nirS and nirK genes. This study provides novel insights by demonstrating that soil cadmium, analogous to beneficial metal micronutrients, effectively alleviates herbicide-induced (especially atrazine) disruptions to the relationships between nitrogen and phosphorus cycling functions in maize fields.