Spatial and Temporal Variability in Atmospheric-Methane-Oxidizing Bacterial Community Structure and Activity in an Alpine Glacier Forefield

Abstract:

High-affinity methane-oxidizing bacteria (MOB) play a crucial role in regulating the sink strength for atmospheric methane (CH₄) in upland soils. Community structure and activity of MOB have been extensively studied in developed soils. However, little is known about their ecosystem service in young, developing soils. Examples of developing soils are found in Alpine glacier forefields, which progressively expand due to glacial retreat. Glacier forefields exhibit diverse geomorphological landforms, which may differ in biogeochemical properties. Also, glacier forefields are subject to seasonal variability in environmental parameters such as soil temperature and water content, which may affect MOB community structure and activity. We recently showed that glacier-forefield soils are a sink for atmospheric CH₄, but a comprehensive understanding of crucial factors affecting MOB community structure and activity is still missing.

In this study we assessed soil-atmosphere CH₄ flux and MOB community structure in three different glacier-forefield landforms (sandhills, floodplains, terraces) throughout a snow-free sampling season. Specifically, we quantified CH₄ flux using the soil-gas-profile method and static flux chambers. The MOB community structure was assessed using next-generation sequencing technology (Illumina-MiSeq^TM) targeting the functional gene pmoA. We observed substantial differences in CH₄ flux between soils of different landforms, with largest fluxes observed in well-drained sandhills (up to ‑2.2 mg CH₄ m^-2 d^-1) and considerably smaller fluxes in other landforms. Methane flux showed a prominent seasonal variability, which was attenuated in older forefield soils. High-diversity MOB communities and a remarkable number of landform-specific operational taxonomic units were found in sandhills, whereas a lower diversity was observed in other landforms. Our phylogenetic analysis suggests the presence of a potentially new group of MOB inhabiting glacier-forefield soils.