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

Area of Science:

• Environmental Science
• Microbiology
• Biogeochemistry

Background:

• Estuarine wetlands store significant carbon but are vulnerable to rising sea levels.
• Sea-level rise can alter methane (CH4) emissions and soil carbon sequestration.
• Sulfate from seawater intrusion may reduce CH4 production, but other factors are influential.

Purpose of the Study:

• To investigate the relationship between salinity and CH4 fluxes in estuarine wetlands.
• To identify microbial drivers of CH4 emissions across a salinity gradient.
• To understand how salinity affects carbon and nitrogen cycling in these ecosystems.

Main Methods:

• Studied 11 wetland complexes across a salinity gradient in the San Francisco Bay and Delta.
• Analyzed CH4 fluxes, methanogen abundance, and functional genes.
• Utilized taxonomic and functional gene data to assess microbial community impacts.

Main Results:

• CH4 fluxes generally decreased with salinity but were highest in oligohaline wetlands (approx. 3-ppt).
• Methanogen genes showed weak correlation with CH4 fluxes, indicating other factors are key.
• Sulfate-reducing fermenters, syntrophic populations, and ammonium dynamics influenced CH4 production and consumption.

Conclusions:

• Low-level salinity intrusion may increase CH4 flux in tidal freshwater wetlands.
• Oligohaline conditions can lead to high CH4 emissions, a concern with ongoing sea-level rise.
• Predicting CH4 fluxes requires accounting for multiple microbial guilds and biogeochemical processes beyond methanogenesis.