151. High Abundances and Expression Levels of Atypical, Non‐Denitrifier N2O Reductases Drive Strong Microbial N2O Consumption Rates in a Minimally Impacted Mangrove Stand.
- Author
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Jameson, Brett D., Lopez, Mark Louie D., Bonderud, Matthew, Stevens, Catherine J., Juniper, S. Kim, Helbing, Caren C., and Grundle, Damian S.
- Subjects
MANGROVE plants ,GENE expression ,COASTAL sediments ,REDUCTASES ,MARINE sediments ,OZONE layer depletion ,CONTINENTAL margins - Abstract
Knowledge of the ecological mechanisms governing N2O cycling in marine sediments lags that of water columns and terrestrial soils, leaving much to be learned about how microbial community dynamics relate to variability in sediment N2O fluxes. The present study assesses these relationships across two distinct environments by focusing on the community structure and activity of N2O reducing microorganisms. The N2O sink capacity of minimally impacted Bermudian mangrove sediments was first estimated using trace‐level microsensors and profile interpretation modeling. Molecular data obtained from these sediments were then compared with those from the Northeast Subarctic Pacific (NESAP) outer continental margin, where previous measurements suggest considerable N2O effluxes. Net N2O uptake was observed for mangrove sediments under ambient and elevated dissolved inorganic nitrogen concentrations (−0.22 ± 0.15 to −0.30 ± 0.26 μmol N2O m−2 d−1), suggesting the microbial potential for N2O consumption exceeded the potential for production via combined nitrification and denitrification. Targeting of bacterial nosZI and nosII gene clusters for quantification using qPCR indicated higher abundance and expression of non‐denitrifier nosZII genes in mangrove sediments demonstrating net N2O uptake. Net N2O production in NESAP sediments was associated with higher abundance and expression of nosZI genes associated with canonical denitrifiers. These results suggest that organisms possessing atypical nosZII genes may act as important N2O scavengers in low‐nitrogen coastal sediments. Plain Language Summary: Nitrous oxide (N2O) is potent greenhouse gas that contributes to ozone depletion in the stratosphere, and atmospheric concentrations a rising as a result of human activities. The production and consumption of N2O in the environment is mediated by microorganisms, and the balance between the two processes is governed by environmental factors such as concentrations of dissolved oxygen and fixed nitrogen. However, little is known about the relationships between microbial community dynamics and rates of N2O production and consumption, especially in sediment environments. We found that minimally impacted mangrove sediments of Bermuda are net consumers of N2O, and continue to consume N2O following short term nitrogen enrichments. This N2O sink capacity was linked to higher abundances and activity levels of atypical N2O reductase genes when compared to sediments that produce N2O. These genes facilitate the consumption of N2O, and frequently occur in microbes that do not have the capacity to produce N2O via denitrification. This study provides further insight into the role of microbial community structure in regulating sediment N2O cycling, and argues for targeted conservation and restoration of coastal systems where sediment environments are in close proximity to the atmosphere. Key Points: The N2O sink capacity of minimally impacted Bermudian mangrove sediments is resilient against modest, short‐term nutrient enrichmentHigh prevalence of non‐denitrifier nosZII genes in mangrove sediments implies a crucial role as N2O scavengers in low‐nitrogen systemsNet N2O production in NESAP sediments is associated with higher expression of nosZI genes associated with canonical denitrifiers [ABSTRACT FROM AUTHOR]
- Published
- 2024
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