Multiple microbial guilds mediate soil methane cycling along a wetland salinity gradient

Journal Article · Mon Jan 22 23:00:00 EST 2024 · mSystems

DOI:https://doi.org/10.1128/msystems.00936-23· OSTI ID:2274993

Hartman, Wyatt H. ^[1]; Bueno de Mesquita, Clifton P. ^[1]; Theroux, Susanna M. ^[1]; Morgan-Lang, Connor ^[2]; Baldocchi, Dennis D. ^[3]; Tringe, Susannah G. ^[4]; Hernandez, ed., Marcela

---

1. DOE Joint Genome Institute, Berkeley, California, USA
2. Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada
3. Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, USA
4. DOE Joint Genome Institute, Berkeley, California, USA, Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA

ABSTRACT

Estuarine wetlands harbor considerable carbon stocks, but rising sea levels could affect their ability to sequester soil carbon as well as their potential to emit methane (CH ₄ ). While sulfate loading from seawater intrusion may reduce CH ₄ production due to the higher energy yield of microbial sulfate reduction, existing studies suggest other factors are likely at play. Our study of 11 wetland complexes spanning a natural salinity and productivity gradient across the San Francisco Bay and Delta found that while CH ₄ fluxes generally declined with salinity, they were highest in oligohaline wetlands (ca. 3-ppt salinity). Methanogens and methanogenesis genes were weakly correlated with CH ₄ fluxes but alone did not explain the highest rates observed. Taxonomic and functional gene data suggested that other microbial guilds that influence carbon and nitrogen cycling need to be accounted for to better predict CH ₄ fluxes at landscape scales. Higher methane production occurring near the freshwater boundary with slight salinization (and sulfate incursion) might result from increased sulfate-reducing fermenter and syntrophic populations, which can produce substrates used by methanogens. Moreover, higher salinities can solubilize ionically bound ammonium abundant in the lower salinity wetland soils examined here, which could inhibit methanotrophs and potentially contribute to greater CH ₄ fluxes observed in oligohaline sediments.

IMPORTANCE

Low-level salinity intrusion could increase CH4 flux in tidal freshwater wetlands, while higher levels of salinization might instead decrease CH4 fluxes. High CH4 emissions in oligohaline sites are concerning because seawater intrusion will cause tidal freshwater wetlands to become oligohaline. Methanogenesis genes alone did not account for landscape patterns of CH4 fluxes, suggesting mechanisms altering methanogenesis, methanotrophy, nitrogen cycling, and ammonium release, and increasing decomposition and syntrophic bacterial populations could contribute to increases in net CH4 flux at oligohaline salinities. Improved understanding of these influences on net CH4 emissions could improve restoration efforts and accounting of carbon sequestration in estuarine wetlands. More pristine reference sites may have older and more abundant organic matter with higher carbon:nitrogen compared to wetlands impacted by agricultural activity and may present different interactions between salinity and CH4. This distinction might be critical for modeling efforts to scale up biogeochemical process interactions in estuarine wetlands.

• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 2274993
• Alternate ID(s): OSTI ID: 2370365
• Journal Information: mSystems, Journal Name: mSystems Journal Issue: 1 Vol. 9; ISSN 2379-5077
• Publisher: American Society for Microbiology
• Country of Publication: United States
• Language: English