Response of microbial biomass to grazing in an alpine meadow along an elevation gradient on the Tibetan Plateau

Abstract

Although grazing is a common land use type, few studies are available about the response of soil microbial biomass to grazing especially above 4300 m on the Tibetan Plateau. Therefore, three fenced enclosures were made at three alpine meadow sites along an elevation gradient (4313 m, winter pasture; 4513 m and 4693 m, summer pasture) in July 2008. Soil samples inside and outside the fenced enclosures were gathered in July, August and September 2011. Microbial biomass C (MBC) and N (MBN) were determined using the chloroform fumigation–extraction method. Grazing marginally declined MBC by 21.60%, 4.83% and 5.36% across sampling dates at elevation 4313 m, 4513 m and 4693 m, respectively. Grazing significantly declined MBN by 39.58% and 18.88% across sampling dates at elevation 4313 m and 4693 m, respectively, whereas it slightly declined MBN by 1.50% at elevation 4513 m. Microbial biomass at elevation 4693 m was significantly higher in comparison with elevation 4513 m and 4313 m, whereas soil temperature at elevation 4693 m was 2.3 °C and 2.8 °C lower than that at elevation 4513 m and 4313 m, respectively. Our findings suggest that MBN may respond more rapidly to grazing than MBC and that climate warming and grazing may decline microbial biomass for the alpine meadow.