Abstract
Seasonally saturated wetlands are hydrologically dynamic ecosystems that provide a variety of ecosystem services; however, their variable hydrologic conditions may promote greenhouse gas emissions. The extent to which wetlands produce and emit greenhouse gases is intimately tied to the underlying microbial community. We established a linear transect spanning a hydrologic gradient on the margins adjacent to five seasonally saturated wetlands to characterize how water level, saturation duration, and frequency of wet-dry cycles influenced the soil and methane-cycling microbial community composition. We found that the soil and methane-cycling microbial community diversity and structure were strongly related to changes in water level and saturation duration but not saturation frequency. Soils that experienced inundation or saturation for more than 50% of the year harbored a soil microbial composition distinct from soils that were rarely saturated or inundated. While soils closer to the wetland basin supported a higher relative abundance of methanogens, methane-oxidizing microbes were present across the entire topographic gradient; however, the composition shifted from a primarily anaerobic to aerobic methanotroph community. Findings suggest that soil and methane cycling microorganisms are influenced by the hydrologic conditions of the soil, with methane producers being restricted to specific ranges and methane oxidizers able to occur under a variety of hydrologic conditions. The mechanisms driving methane oxidation by the latter, however, may depend on the hydrologic conditions.
Highlights
Flooded or saturated wetlands temporarily hold water from fall to late spring and dry up periodically when evapotranspiration exceeds surface and groundwater inputs (Calhoun et al, 2017)
Methane oxidation was believed to be restricted to oxygen-rich soil environments; new evidence suggests that anaerobic oxidation of methane (AOM) may consume a much larger fraction of CH4 produced in freshwater environments, including wetland soils, than initially expected (Smemo and Yavitt, 2011; Cui et al, 2015; Wang et al, 2018)
Our analysis suggests that soil microbial community diversity, richness, and composition were strongly related to soil organic matter (SOM) content; because SOM and hydrology are typically related, it is difficult to discern the link between hydrology, organic matter and microbial populations (Fierer et al, 2003; Bossio et al, 2006; Balasooriya et al, 2007)
Summary
Flooded or saturated wetlands (e.g., vernal pools, wet prairies, and Carolina and Delmarva bays) temporarily hold water from fall to late spring and dry up periodically when evapotranspiration exceeds surface and groundwater inputs (Calhoun et al, 2017). Such dynamic hydroperiods influence every aspect of these systems – from the ecology and breeding success of amphibian species (Chandler et al, 2017) to soil nutrient cycling (Marton et al, 2015; Hansen et al, 2018). Methane oxidation was believed to be restricted to oxygen-rich soil environments; new evidence suggests that anaerobic oxidation of methane (AOM) may consume a much larger fraction of CH4 produced in freshwater environments, including wetland soils, than initially expected (Smemo and Yavitt, 2011; Cui et al, 2015; Wang et al, 2018)
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