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Applied and Environmental Microbiology, November 2008, p. 6690-6696, Vol. 74, No. 21
0099-2240/08/$08.00+0     doi:10.1128/AEM.00797-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Soil Formate Regulates the Fungal Nitrous Oxide Emission Pathway{triangledown}

W. K. Ma, R. E. Farrell, and S. D. Siciliano*

Department of Soil Science, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5A8, Canada

Received 7 April 2008/ Accepted 2 September 2008

Fungal activity is a major driver in the global nitrogen cycle, and mounting evidence suggests that fungal denitrification activity contributes significantly to soil emissions of the greenhouse gas nitrous oxide (N2O). The metabolic pathway and oxygen requirement for fungal denitrification are different from those for bacterial denitrification. We hypothesized that the soil N2O emission from fungi is formate and O2 dependent and that land use and landforms could influence the proportion of N2O coming from fungi. Using substrate-induced respiration inhibition under anaerobic and aerobic conditions in combination with 15N gas analysis, we found that formate and hypoxia (versus anaerobiosis) were essential for the fungal reduction of 15N-labeled nitrate to 15N2O. As much as 65% of soil-emitted N2O was attributable to fungi; however, this was found only in soils from water-accumulating landforms. From these results, we hypothesize that plant root exudates could affect N2O production from fungi via the proposed formate-dependent pathway.

* Corresponding author. Mailing address: Department of Soil Science, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada. Phone: (306) 966-4035. Fax: (306) 966-6881. E-mail: steven.siciliano{at}usask.ca

{triangledown} Published ahead of print on 12 September 2008.

Applied and Environmental Microbiology, November 2008, p. 6690-6696, Vol. 74, No. 21
0099-2240/08/$08.00+0     doi:10.1128/AEM.00797-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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