Biochar remediates denitrification process and N2O emission in pesticide chlorothalonil-polluted soil: Role of electron transport chain

Agricultural production causes large amounts of pesticide residues into soil, disturbing soil denitrification and N2O emission. Recently, biochar amendment has been regarded as the effective way to stimulate soil denitrification and reduce N2O emission. However, the underlying mechanism has not been well understood. Here, the effects of biochar on denitrification and N2O emission in the chlorothalonil (CHT)-polluted soil were explored. Biochar (50 g kg(-1)) was added to soil at the beginning of the experiment, and CHT (5 and 25 mg kg(-1)) was repeatedly applied to soil at the 30-day interval for 105 days. The obtained results showed that CHT remarkably declined soil respiration rates (52-77%) and denitrification rates (50-56%), but increased N2O emissions by 820-1030%. After biochar application, however, soil denitrification rates were increased by 13-26%, and N2O emissions were declined by 442-809% compared with non-biochar spiked soils. A further mechanism study indicated that biochar remarkably promoted the activities of microbial electron transfer chain, electron transporters (complex I, II, III and cytochrome c), and four denitrifying reductases (NAR, NIR, NOR, NOS) in CHT-polluted soils, suggesting that electron transport and consumption capacities during denitrification were stimulated by biochar. Soil denitrification was thus improved and N2O emission was subsequently reduced. Furthermore, biochar significantly upregulated soil denitrifying gene abundances and increased denitrifiers abundances (i.e., Enterobacter and Pseudarthrobacter). Overall, this work will promote the current understandings of molecular mechanisms through which N2O emission in pesticide contaminated soils responds to biochar remediation.