Denitrifying woodchip bioreactors (WBRs) are increasingly used to manage the release of non‐point source nitrogen (N) by stimulating microbial denitrification. Woodchips serve as a renewable organic carbon (C) source, yet the recalcitrance of organic C in lignocellulosic biomass causes many WBRs to be C‐limited. Prior studies have observed that oxic–anoxic cycling increased the mobilization of organic C, increased nitrate (NO3−) removal rates, and attenuated production of nitrous oxide (N2O). Here, we use multi‐omics approaches and amplicon sequencing of fungal 5.8S‐ITS2 and prokaryotic 16S rRNA genes to elucidate the microbial drivers for enhanced NO3−removal and attenuated N2O production under redox‐dynamic conditions. Transient oxic periods stimulated the expression of fungal ligninolytic enzymes, increasing the bioavailability of woodchip‐derived C and stimulating the expression of denitrification genes. Nitrous oxide reductase (
Rivers and streams act as globally significant sources of nitrous oxide (N2O) to the atmosphere, in part through denitrification reactions that will increase in response to ongoing anthropogenic nitrogen loading. While many factors that contribute to the release of N2O relative to inert dinitrogen (N2) are well described, the ability to predict N2O yields from streams remains a fundamental challenge. Here, I revisit results from the second Lotic Intersite Nitrogen eXperiments (LINX II) in the context of turbulent hyporheic exchange. Denitrification efficiency, or the fraction of nitrate delivered to the streambed by stream turbulence that is chemically reduced, emerges as the single best predictor of N2O yields and underpins the first statistically significant models of inter‐site N2O yields. This mechanistic connection is supported by reactive transport modeling of hyporheic zone denitrification representing advective flowpaths, flowpath mixing, and diffusion‐dominated anoxic microzones. Simulated N2O yields are inversely correlated with denitrification efficiency; however, advective models are unable to capture low LINX II N2O yields at low denitrification efficiencies. Hyporheic zone mixing exacerbates this inability to capture observed N2O yields via the promotion of N2O release from fast, oxic flowpaths. Instead, anoxic microzones are required to account for LINX II observations through consistently low N2O yields and the consumption of upstream‐produced N2O. Together, these results provide a framework for controls on stream N2O yields and suggest that stream corridor restoration designs aimed at increasing the capacity of hyporheic zones to remediate nitrate loading, as opposed to increasing hyporheic exchange, will also reduce proportional N2O emissions.
more » « less- Award ID(s):
- 2103520
- NSF-PAR ID:
- 10448179
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- AGU Advances
- Volume:
- 2
- Issue:
- 4
- ISSN:
- 2576-604X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract nosZ ) genes were primarily clade II, and the ratio of clade II/clade InosZ transcripts during the oxic–anoxic transition was strongly correlated with the N2O yield. Analysis of metagenome‐assembled genomes revealed that many of the denitrifying microorganisms also have a genotypic ability to degrade complex polysaccharides like cellulose and hemicellulose, highlighting the adaptation of the WBR microbiome to the ecophysiological niche of the woodchip matrix. -
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