Different responses of soil element contents and their stoichiometry (C:N:P) to yak grazing and Tibetan sheep grazing in an alpine grassland on the eastern Qinghai - Tibetan Plateau'

The alpine grassland of the Qinghai-Tibetan Plateau has long been subjected to grazing by local livestock, yak and Tibetan sheep. Although there is plenty of evidence that grazing influences the vegetation community structure and functions, researches on how grazing of different livestock affects element contents in soil and their stoichiometry and how they relate to plant community remain inadequate in the region. We quantified the concentration and distribution of carbon (C), nitrogen (N) and phosphorus (P), and investigated the robustness of soil stoichiometry (C:N:P) under yak grazing and Tibetan sheep grazing through a manipulated grazing experiment on an alpine grassland. Our results showed that: (1) Yak grazing increased the soil total carbon content (STC) but decreased the soil total phosphorus content (STP), whereas Tibetan sheep grazing decreased STC but increased STP. Neither of the two livestock species had impact on the soil total nitrogen content (STN). (2) Yak grazing and sheep grazing had no impact on soil stoichiometry except for C:P. (3) Only STP and C:P were affected by the mixing ratio of yak to sheep. The plant biomass loss and the shifts in plant community structure may account for the opposite responses of STC and STP to yak grazing and sheep grazing, whereas the dung chemical property of different livestock species might also contribute to the response of STP. The higher soil C:N and lower soil N:P ratios indicated that plant growth may be limited more by N than by P in the region.