Acute response of soil denitrification and N₂O emissions to chlorothalonil: A comprehensive molecular mechanism

The fungicide chlorothalonil (CHT) has been widely used in the tea orchard due to its high-efficiency and sterilization. It has been reported that repeated application of CHT inhibits soil nitrification process. However, the acute impact of CHT on soil denitrification and associated N₂O emissions is unclear. This study evaluated nitrate (NO₃^-) removal, denitrifying gene abundance and denitrifying enzyme activity of tea orchard soil after a 72-h-exposure to CHT. It was found that increasing CHT from 5 to 25 mg kg^-1 suppressed the NO₃^- removal efficiency from 74.6% to 54.1%, but increased N₂O emissions from 23.1% to 94.8%. Following treatment with 25 mg kg^-1 of CHT, the abundances of the nirK, nirS and nosZ genes were reduced by 31.6%, 22.1%, and 50.7%, respectively. Alternatively, the declines of the electron transport system activity (ETSA) value and adenosine triphosphate (ATP) content suggested that CHT had an inhibitory effect on microbial metabolism. Enzyme activity studies further revealed that the decrease of nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR) activities was the main reason for the suppression of denitrification by CHT. Furthermore, positive correlations were observed between denitrifying reductase activity and the intracellular metabolism, indicating that the decrease in microbial metabolism should also be responsible for the inhibitory effect of CHT on the denitrifying process. Overall, it was found that the acute exposure of soil to CHT could inhibit the denitrification process and significantly increase N₂O emissions, which might result in destruction of the soil nitrogen cycle and exacerbation of global warming.