Livestock grazing on alpine soils causes changes in abiotic and biotic soil properties and thus in abundance and activity of microorganisms engaged in the methane cycle

Abstract

Three subalpine soils with similar properties and climate conditions, but with different land use were chosen for assessing the abundance and activity of aerobic and anaerobic microorganisms, particularly of methanotrophic Bacteria and methanogenic Archaea. Within these three soils, there was a distinct gradient in grazing and manure input that ranged from abandoned site (no grazing) to pasture (intense grazing) and included also a meadow (moderate grazing). Activities of dehydrogenase and ammonification indicated higher microbial activities in soil from the abandoned site than in the pasture and in the meadow soil. These differences in microbial activity between unmanaged and managed soils additionally increased during the growing season. Our results show that temperature and soil water content significantly influence methane production and that the grazing gradient is an additional important factor. At 50 °C and under water-saturated conditions, methane production reached 4.42 ± 0.09 ml g−1 dry weight in the pasture soil samples after 6 weeks. By contrast, low methane production was detected in soil from the abandoned site, whereas the meadow values were intermediate. Additionally, methanotrophic activities were investigated under an aerobic atmosphere with 5% CH4 and led to the surprising result that methane oxidation only occurred in undisturbed soils, whereas all sieved soil samples even produced further methane.