INTEGRATED AGRICULTURAL SYSTEMS FOR THE NORTHERN GREAT PLAINS
Location: Northern Great Plains Research Laboratory
Title: Co-occurring anammox, denitrification and codenitrification in agricultural soils
Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 10, 2012
Publication Date: January 1, 2013
Citation: Long, A., Heitman, J., Tobias, C., Phillips, B.L., Song, B.K. 2013. Co-occurring anammox, denitrification and codenitrification in agricultural soils. Microbial Ecology. 79(1):168-176.
Interpretive Summary: The fate of nitrogen in soil is important to agricultural productivity, yet it is unclear how different groups of soil organisms metabolize and transform nitrogen. On way nitrogen is removed from the soil is through a process called denitrification. Other ways include anammox and codentrification. Many have focused on bacterial denitrification, but few have investigated the role of anammox and codenitrification in agricultural soils. We investigated several microbial processes and microbial abundances and found fungal codenitrification contributed more to di-nitrogen gas production than bacterial denitrification. This study helps us to understand important bacterial-fungal linkages and microbial processes involving transformation of nitrogen in soils.
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 of generating N2 from soils. However, fungal codenitrification and denitrification have not been well investigated in agricultural soils. To evaluate bacterial and fungal processes of N2 production, molecular and 15N isotope analyses were conducted with soil samples collected from six different agricultural fields in the USA. The abundance of denitrifying and anammox bacteria was measured based on quantitative PCR of nitrous oxide reductase (nosZ) and hydrazine oxidase (hzo) genes, respectively, while the internal transcribed spacer (ITS) of Fusarium oxysporum was quantified to estimate the abundance of codenitrifying and denitrifying fungi. 15N tracer incubation experiments with 15NO3- or 15NH4+ addition were conducted to measure the rates of N2 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-N g-1 d-1, while the combined potential rates of anammox and codenitrification ranged from 2.796 to 147.711 nmoles N2-N g-1 d-1. Soil incubation experiments with antibiotics indicated that fungal codenitrification was the primary process contributing to N2 production in the North