Reconnaissance of Oxygenic Denitrifiers in Agriculturally Impacted Soils.

Row crop production in the agricultural Midwest pollutes waterways with nitrate, and exacerbates climate change through increased emissions of nitrous oxide and methane. Oxygenic denitrification processes in agricultural soils mitigate nitrate and nitrous oxide pollution by short-circuiting the canonical pathway to avoid nitrous oxide formation. Furthermore, many oxygenic denitrifiers employ a nitric oxide dismutase () to create molecular oxygen that is used by methane monooxygenase to oxidize methane in otherwise anoxic soils. The direct investigation of genes that could facilitate oxygenic denitrification processes in agricultural sites is limited, with no prior studies investigating genes at tile drainage sites. Thus, we performed a reconnaissance of genes at variably saturated surface sites, and within a variably to fully saturated soil core in Iowa to expand the known distribution of oxygenic denitrifiers. We identified new gene sequences from agricultural soil and freshwater sediments in addition to identifying nitric oxide reductase (qNor) related sequences. Surface and variably saturated core samples displayed a to 16S rRNA gene relative abundance of 0.004% to 0.1% and fully saturated core samples had relative gene abundance of 1.2%. The relative abundance of the phylum increased from 0.6% and 1% in the variably saturated core samples to 3.8% and 5.3% in the fully saturated core samples. The more than 10-fold increase in relative abundance and almost 9-fold increase in relative abundance in fully saturated soils suggests that potential oxygenic denitrifiers play a greater nitrogen cycling role under these conditions. The direct investigation of genes in agricultural sites is limited, with no prior studies investigating genes at tile drains. An improved understanding of gene diversity and distribution is significant to the field of bioremediation and ecosystem services. The expansion of the gene database will advance oxygenic denitrification as a potential strategy for sustainable nitrate and nitrous oxide mitigation, specifically for agricultural sites.