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 (
- Award ID(s):
- 1804975
- NSF-PAR ID:
- 10382099
- Date Published:
- Journal Name:
- Environmental Science: Water Research & Technology
- Volume:
- 7
- Issue:
- 12
- ISSN:
- 2053-1400
- Page Range / eLocation ID:
- 2357 to 2371
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
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. -
more » « less
Abstract Oxygen (O2) limitation contributes to persistence of large carbon (C) stocks in saturated soils. However, many soils experience spatiotemporal O2 fluctuations impacted by climate and land‐use change, and O2‐mediated climate feedbacks from soil greenhouse gas emissions remain poorly constrained. Current theory and models posit that anoxia uniformly suppresses carbon (C) decomposition. Here we show that periodic anoxia may sustain or even stimulate decomposition over weeks to months in two disparate soils by increasing turnover and/or size of fast‐cycling C pools relative to static oxic conditions, and by sustaining decomposition of reduced organic molecules. Cumulative C losses did not decrease consistently as cumulative O2exposure decreased. After >1 year, soils anoxic for 75% of the time had similar C losses as the oxic control but nearly threefold greater climate impact on a CO2‐equivalent basis (20‐year timescale) due to high methane (CH4) emission. A mechanistic model incorporating current theory closely reproduced oxic control results but systematically underestimated C losses under O2 fluctuations. Using a model‐experiment integration (ModEx) approach, we found that models were improved by varying microbial maintenance respiration and the fraction of CH4production in total C mineralization as a function of O2availability. Consistent with thermodynamic expectations, the calibrated models predicted lower microbial C‐use efficiency with increasing anoxic duration in one soil; in the other soil, dynamic organo‐mineral interactions implied by our empirical data but not represented in the model may have obscured this relationship. In both soils, the updated model was better able to capture transient spikes in C mineralization that occurred following anoxic–oxic transitions, where decomposition from the fluctuating‐O2treatments greatly exceeded the control. Overall, our data‐model comparison indicates that incorporating emergent biogeochemical properties of soil O2variability will be critical for effectively modeling C‐climate feedbacks in humid ecosystems.
-
more » « less
Abstract For many glacial lakes with highly permeable sediments, water exchange rates control hydrologic residence times within the sediment‐water interface (SWI) and the removal of reactive compounds such as nitrate, a common pollutant in lakes and groundwater. Here we conducted a series of focused tracer injection experiments in the upper 20 cm of the naturally downwelling SWI in a flow‐through lake on Cape Cod, MA. We systematically varied residence time and reactant controls on nitrate processing, using isotopically labeled15N nitrate to monitor the effect of these changes on nitrate removal via denitrification. The addition of acetate, a labile carbon compound, triggered the lake SWI to switch from net production to net removal of nitrate. When acetate was combined with increased residence time created by controlled reductions in water flux, we observed a fivefold increase in nitrate removal, a 26‐fold increase in N2production, and a 42‐fold increase in N2O production. We demonstrate that water residence time is an important control on the fate of nitrate in these lake SWIs and illustrate that seasonal conditions that alter lake exchange rates and variability in lake carbon may predict dynamic nitrate removal across the SWI. Additionally, observed N2O production during the oxic pore water experiments paired with geophysical characterization of the sediment porosity revealed that the lake SWI has less mobile pores occupying upward of 50% of the total porosity volume, which function as reactive microzones for nitrate processing.
-
null (Ed.)Abstract The ocean is a net source of N 2 O, a potent greenhouse gas and ozone-depleting agent. However, the removal of N 2 O via microbial N 2 O consumption is poorly constrained and rate measurements have been restricted to anoxic waters. Here we expand N 2 O consumption measurements from anoxic zones to the sharp oxygen gradient above them, and experimentally determine kinetic parameters in both oxic and anoxic seawater for the first time. We find that the substrate affinity, O 2 tolerance, and community composition of N 2 O-consuming microbes in oxic waters differ from those in the underlying anoxic layers. Kinetic parameters determined here are used to model in situ N 2 O production and consumption rates. Estimated in situ rates differ from measured rates, confirming the necessity to consider kinetics when predicting N 2 O cycling. Microbes from the oxic layer consume N 2 O under anoxic conditions at a much faster rate than microbes from anoxic zones. These experimental results are in keeping with model results which indicate that N 2 O consumption likely takes place above the oxygen deficient zone (ODZ). Thus, the dynamic layer with steep O 2 and N 2 O gradients right above the ODZ is a previously ignored potential gatekeeper of N 2 O and should be accounted for in the marine N 2 O budget.more » « less
-
more » « less
Abstract This study evaluates rates and pathways of methane (CH4) oxidation and uptake using14C‐based tracer experiments throughout the oxic and anoxic waters of ferruginous Lake Matano. Methane oxidation rates in Lake Matano are moderate (0.36 nmol L−1 day−1to 117 μmol L−1 day−1) compared to other lakes, but are sufficiently high to preclude strong CH4fluxes to the atmosphere. In addition to aerobic CH4oxidation, which takes place in Lake Matano's oxic mixolimnion, we also detected CH4oxidation in Lake Matano's anoxic ferruginous waters. Here, CH4oxidation proceeds in the apparent absence of oxygen (O2) and instead appears to be coupled to some as yet uncertain combination of nitrate (
), nitrite ( ), iron (Fe) or manganese (Mn), or sulfate ( ) reduction. Throughout the lake, the fraction of CH4carbon that is assimilated vs. oxidized to carbon dioxide (CO2) is high (up to 93%), indicating extensive CH4conversion to biomass and underscoring the importance of CH4as a carbon and energy source in Lake Matano and potentially other ferruginous or low productivity environments.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d1ew00446h
