The influence of cattle grazing on methane fluxes and engaged microbial communities in alpine forest soils

Abstract

Recent dynamics and uncertainties in global methane budgets necessitate a dissemination of the current knowledge about the controls of sources and sinks of atmospheric methane.Forest soils are considered to be efficient methane sinks; however, as they are microbially mediated they are sensitive to anthropogenic influences and tend to switch from being sinks to being CH₄ sources. Regarding global changes in land use, the present study aimed at (i) investigating the influence of grazing on flux rates of methane in forest soils (ii) deducing possible (a)biotic factors regulating these fluxes, and (iii) gaining an insight into the complex interactions between CH₄-cycling microorganisms and ecosystem functioning. Here we show that even very extensive grazing significantly mitigated the soils sink strength for atmospheric methane through alterations of both microbial activity and community composition. In situ flux measurements revealed that all native, non-grazed areas were net methane consumers, while the adjacent, grazed areas were net methane producers. Whereas neither parent material nor soil properties including moisture and organic matter showed any correlation to the ascertained fluxes, significantly higher archaeal abundances at the grazed study sites indicated that small inputs of methanogens associated with cattle grazing may be sufficient to sustainably increase methane emissions.

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