Mechanisms of N2O production following chloropicrin fumigation

Soil fumigation has recently been shown to affect the greenhouse gas balance by increasing emissions of nitrous oxide (N2O) following chloropicrin (CP) application. However, the exact mechanisms of this increase were not investigated. The purpose of this study was to elucidate potential mechanisms of CP-induced N2O production through laboratory incubations using chemical inhibitors (acetylene, antibacterial, antifungal, and oxygen), isotopically labeled 15N-CP, and pH modifications of a forest nursery soil. Results showed that N2O production increased by 12.6 times following CP fumigation. Microbial activity contributed 82% to the CP-induced N2O production, with the remaining 18% from abiotic processes as determined by incubation with sterilized soil. Inhibitor studies suggested that 20% of the N2O production was from bacteria and 70% from fungi. There were no significant differences in N2O production following CP fumigation under various levels of acetylene (0, 10, and 10 kPa), suggesting that traditional nitrification and denitification reactions did not significantly contribute to N2O production following CP fumigation. 15N labeled studies indicated that 12% of fumigant source N was incorporated into the produced N2O. No enrichment in N2 was observed, indicating that N2O was one of the terminal biotic mineralization products of CP. Production of N2O is aerobic and production rates increased with increasing oxygen concentrations. Our data strongly suggested that fungal mediated denitrification reactions under aerobic conditions were the primary mechanism for CP-induced N2O production.