Key players of methane dynamics in alpine fens: interaction of vascular plants and microbial communities

Abstract:

Natural wetlands are important emitters of the potent greenhouse gas methane (CH₄), contributing an estimated 26 - 42% to the global emissions. In these habitats CH₄ is generated by methanogenic archaea mediating the terminal steps of organic matter degradation under anoxic conditions. The produced CH₄ is partly oxidized by methanotrophic bacteria in oxic zones, thereby mitigating CH₄ release. Various factors can influence CH₄ emissions from wetlands, including the presence of vascular plants, as their aerenchyma can serve as conduits for CH₄ release to the atmosphere. In the present study, we investigated the CH₄ dynamics in two Swiss alpine fens (1900 - 2300 m a.s.l), and sampling locations within these fens were characterized by distinct dominant vascular plants, namely Carex spp. and Eriophorum spp.. Analyses of the microbial communities present in the fen soils were complemented by in situ measurements of CH₄ emissions and analyses of physico-chemical pore water properties. Methane emissions and pore water concentrations varied depending on fen and dominating plant species, with generally higher CH₄ emissions observed from the Carex dominated locations. Active methanotrophic and methanogenic microorganisms (transcripts of specific marker genes) were detected at different depths, independent of O₂ and CH₄ pore water concentrations. The expected separation of oxic methanotrophic and anoxic methanogenic zones was not observed. Yet, composition analyses of the different communities showed a clear clustering according to fen and dominating plant species. Within each location, variation of composition with depth was only observed for the methanogenic communities. Detailed profiling of CH₄ emissions with respect to changes in light and temperature is currently being carried out. Our results represent a comprehensive in situ study on factors affecting CH₄ emissions from alpine fens, highlighting the influence of vascular plants on the microbial communities involved.