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Title:   Author  item
                                            SPOKAS, KURT - UNIV OF MINNESOTAitem
                                            WANG, D - UNIV OF MINNESOTAitem
                                            Venterea, Rodney

                                                         - *Rod*item
                                            SADOWSKY, M - UNIV OF MINNESOTA
  Submitted to: Applied Soil Ecology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 3/25/2005
                                    Publication  Date: 1/1/2006
                                    Citation: Spokas, K., Wang, D., Venterea, R.T., Sadowsky, M. 2006. Mechanisms of N2O production following chloropicrin fumigation. Applied Soil Ecology. 31:101-109.Interpretive Summary: Agricultural pesticides that are applied in gaseous form may subsequently escape to the atmosphere and have various environmental impacts. Several of these so-called 'fumigants' are currently being evaluated as replacements for methyl bromide (MeBr), which has been slated to be phased out due to its potential role in stratospheric ozone depletion. In a previous study, we showed that one of these MeBr alternatives (Chloropicrin, CP) stimulated the production of nitrous oxide (N2O), which is a very potent greenhouse gas. The purpose of the current study was to elucidate the underlying biological and chemical mechanisms responsible for the previously observed CP-induced N2O production. Through the use of differential microbial inhibitors and stable isotope methods, we conclude that the majority (~ 70 %) of N2O produced following CP application was due to fungal mediated denitrification reactions, with the remaining contributed by aerobic bacteria and abiotic sources. Traditional bacterial nitrification and denitrification reactions did not significantly contribute to N2O production. These results will impact policy-makers and scientists evaluating MeBr alternatives.  They will need to consider the potential for CP to stimulate emissions of N2O via a variety of biochemical mechanisms.
                                Technical Abstract: Soil fumigation has recently been shown to affect the greenhouse gas balance by increasing emissions of nitrous oxide (N2O) following chloropicrin (CP) application. 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 Pa, 10 Pa, and 10 kPa), suggesting that traditional nitrification and denitrification reactions did not significantly contribute to N2O production after CP fumigation. 15N labeled studies indicated that 12% of fumigant source N was incorporated into N2O, and that no enrichment in N2 was observed, indicating that N2O was one of the terminal 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.


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