Effects of Clay Content and Plant Litter Quality on Methanogen Community Composition and Functional Gene Abundance in Natural and Restored Tidal Freshwater Wetland Soils.

Methanogens play an important role in wetland carbon (C) cycling because they help catalyze decomposition of soil organic matter (SOM) and are the main biological drivers of methane (CH₄) production. Methane is a potent greenhouse gas and CH₄ emissions can differ greatly between tidal freshwater wetlands (TFWs). Due to the limited global extent of TFWs they are not currently a significant global source of CH₄, but significant changes to soil habitat and plant community composition during wetland restoration have unknown consequences on CH₄production and subsequent emissions. Additionally, the composition and quantity of methanogens in TFW soils are not well understood.

This study examined the effects of plant species (Phragmites australis and Peltandra virginica), soil texture (specifically clay content), and site history (natural or restored TFW) on methanogen community composition, gene abundance, and CH₄emission. Soil samples from two TFWs – one natural and one restored – were used to construct anaerobic laboratory mesocosms. The restored TFW mesocosms were set up with plant leaf litter and soil texture treatments, while soils from the natural TFW were only subjected to leaf litter treatments. Methane emission was monitored for 9 weeks and mesocosms were destructively sampled after 14, 34, or 62 days of incubation. For each sample, we estimated archaeal, and methanogen gene abundance using quantitative PCR (qPCR), and whole community composition was characterized targeting the 16S rDNA v4 region.

Total methane production showed that the restored soil produced significantly more CH₄ than the natural soil. In addition, total greenhouse gas emission was affected by leaf litter but not clay content. Based on methane emission data, we expect methanogen gene abundance to increase over time. However, we observed a decrease in overall archaeal DNA quantities over time, and we expect that this is because of a decline in methanogen community diversity.