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Co-occurring Anammox, Denitrification, and Codenitrification in Agricultural Soils

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Anammox and denitrification mediated by bacteria are known to be the major microbial processes converting fixed N to N2 gas in various ecosystems. Codenitrification and denitrification by fungi are additional pathways ofgenerating N2 from soils. However, fungal codenitrification and denitrification have not been well investigated in agricultural soils. To evaluate bacterial and fungal processes ofN2 production, molecular and l~ isotope analyses were conducted with soil samples collected from six different agricultural fields in the USA. The abundance ofdenitrifying and anammox bacteria was measured based on quantitative PCR ofnitrous oxide reductase (nosZ) and hydrazine oxidase (hzo) genes, respectively, while the internal transcribed spacer (ITS) of Fusarium oxysporum was quantified to estimate the abundance ofcodenitrifying and denitrifying fungi. l~ tracer incubation experiments with I~03-or l~+ addition were conducted to measure the rates ofN2 production from anammox, denitrification and codenitrification. In addition, soil incubation experiments with antibiotic treatments were used to differentiate between fungal and bacterial N2 productions in soil samples collected from a selected site in North Carolina, USA. Denitrifying bacteria were found to be the most abundant followed by F. oxysporum based on the qPCR assays. The potential denitrification rates by bacteria and fungi ranged from 4.118 to 42.121 nmoles N2-Ng-l d-l, while the combined potential rates ofanammox and codenitrification ranged from 2.796 to 147.711 nmoles Nr N g-1 d-l. Soil incubation experiments with antibiotics indicated that fungal codenitrification was the primary process contributing to N2 production in the North Carolina soil. This study clearly demonstrates the importance offungal processes in the agricultural N cycle.
Andrew Long , Joshua Heltman , Craig Toblas , Rebecca Philips , Bongkeun Song
USDA Scientist Submission
Applied and environmental microbiology 2013 Jan. v.79 no.1
American Society for Microbiology.
Journal Articles, USDA Authors, Peer-Reviewed
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