Disturbances of electron production, transport and utilization caused by chlorothalonil are responsible for the deterioration of soil denitrification

Extensive use of pesticides poses significant threats to soil denitrification process and might affect the emission of the greenhouse gas nitrous oxide (N2O) from soils. Previous studies on soil denitrification have frequently focused on natural factors or nitrogen fertilization, but have ignored the role of pesticides. In this study, the effects of chlorothalonil (CHT, a common pesticide) and its major metabolite 4-hydroxychlorothalonil (4OH-CHT) on soil denitrification were explored. Results showed that soil denitrification rates (N-15 pairing method) were declined by 27.4%-72.2%, whereas N2O emissions were unexpectedly increased by 83.9%-299.5%. These disturbances were caused by CHT, rather than by its metabolite 40H-CHT, and noncompetitive inhibition was observed with an inhibition constant of 9.74 mg kg(-1). Mechanistic studies further revealed that CHT inhibited soil denitrification process by deteriorating organic matter metabolism (electron production), electron respiration chain (electron transport), and denitrifying enzymes activities (electron utilization), more than by influencing denitrifier communities and denitrifying gene abundances. Furthermore, structural equation modeling suggested that electron respiration chain and N2O reductase activities were the most important drivers in explaining denitrification in CHT-polluted soils. Our results imply that the wide use of pesticides in agricultural production may disturb soil nitrogen cycle and increase the production of potent greenhouse gas N2O.