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Carbon-sink potential of continuous alfalfa agriculture lowered by short-term nitrous oxide emission events.

ABSTRACT: Alfalfa is the most widely grown forage crop worldwide and is thought to be a significant carbon sink due to high productivity, extensive root systems, and nitrogen-fixation. However, these conditions may increase nitrous oxide (N₂O) emissions thus lowering the climate change mitigation potential. We used a suite of long-term automated instrumentation and satellite imagery to quantify patterns and drivers of greenhouse gas fluxes in a continuous alfalfa agroecosystem in California. We show that this continuous alfalfa system was a large N₂O source (624 ± 28 mg N₂O m² y^-1), offsetting the ecosystem carbon (carbon dioxide (CO₂) and methane (CH₄)) sink by up to 14% annually. Short-term N₂O emissions events (i.e., hot moments) accounted for ≤1% of measurements but up to 57% of annual emissions. Seasonal and daily trends in rainfall and irrigation were the primary drivers of hot moments of N₂O emissions. Significant coherence between satellite-derived photosynthetic activity and N₂O fluxes suggested plant activity was an important driver of background emissions. Combined data show annual N₂O emissions can significantly lower the carbon-sink potential of continuous alfalfa agriculture.

SUBMITTER: Anthony TL

PROVIDER: S-EPMC10079834 | biostudies-literature | 2023 Apr

REPOSITORIES: biostudies-literature

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Carbon-sink potential of continuous alfalfa agriculture lowered by short-term nitrous oxide emission events.

Anthony Tyler L TL Szutu Daphne J DJ Verfaillie Joseph G JG Baldocchi Dennis D DD Silver Whendee L WL

Nature communications 20230406 1

Alfalfa is the most widely grown forage crop worldwide and is thought to be a significant carbon sink due to high productivity, extensive root systems, and nitrogen-fixation. However, these conditions may increase nitrous oxide (N<sub>2</sub>O) emissions thus lowering the climate change mitigation potential. We used a suite of long-term automated instrumentation and satellite imagery to quantify patterns and drivers of greenhouse gas fluxes in a continuous alfalfa agroecosystem in California. We ...[more]

PMID: 37024458

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Project description:BackgroundFirmicutes have the capacity to remove excess nitrate from the environment via either denitrification, dissimilatory nitrate reduction to ammonium or both. The recent renewed interest in their nitrogen metabolism has revealed many interesting features, the most striking being their wide variety of dissimilatory nitrate reduction pathways. In the present study, nitrous oxide production from Bacillus licheniformis, a ubiquitous Gram-positive, spore-forming species with many industrial applications, is investigated.ResultsB. licheniformis has long been considered a denitrifier but physiological experiments on three different strains demonstrated that nitrous oxide is not produced from nitrate in stoichiometric amounts, rather ammonium is the most important end-product, produced during fermentation. Significant strain dependency in end-product ratios, attributed to nitrite and ammonium, and medium dependency in nitrous oxide production were also observed. Genome analyses confirmed the lack of a nitrite reductase to nitric oxide, the key enzyme of denitrification. Based on the gene inventory and building on knowledge from other non-denitrifying nitrous oxide emitters, hypothetical pathways for nitrous oxide production, involving NarG, NirB, qNor and Hmp, are proposed. In addition, all publically available genomes of B. licheniformis demonstrated similar gene inventories, with specific duplications of the nar operon, narK and hmp genes as well as NarG phylogeny supporting the evolutionary separation of previously described distinct BALI1 and BALI2 lineages.ConclusionsUsing physiological and genomic data we have demonstrated that the common soil bacterium B. licheniformis does not denitrify but is capable of fermentative dissimilatory nitrate/nitrite reduction to ammonium (DNRA) with concomitant production of N2O. Considering its ubiquitous nature and non-fastidious growth in the lab, B. licheniformis is a suitable candidate for further exploration of the actual mechanism of N2O production in DNRA bacteria and its relevance in situ.

Dataset Information

Carbon-sink potential of continuous alfalfa agriculture lowered by short-term nitrous oxide emission events.

Publications

Carbon-sink potential of continuous alfalfa agriculture lowered by short-term nitrous oxide emission events.

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