关键词: 生态系统多功能性, 植物多样性, 藏北高寒草地, 围栏封育与自由放牧, 平均值法, 多阈值法

Abstract: To investigate the impacts of grazing exclusion on the multifunctionality of ecosystems, 11 indicators related to nutrient cycling and productivity, including aboveground biomass, soil pH, soil bulk density, moisture content, total soil carbon, total soil phosphorus, available phosphorus, total soil nitrogen, inorganic nitrogen, ammonium nitrogen, and nitrate nitrogen, were selected and measured from grazing exclusion and free grazing sample plots of four grassland types （alpine meadow, alpine meadow steppe, alpine steppe, and alpine desert steppe） in the rainfall gradient zone in Northern Xizang. The average value method and multi-threshold method were utilized to explore the effects of grazing exclusion on the multifunctionality of ecosystems. The results showed that plant diversity, species richness and ecosystem multifunctionality of alpine grasslands all decreased significantly with decreasing precipitation （P<0.05）. Grazing exclusion increased plant diversity and richness as well as aboveground biomass. Ecosystem multifunctionality was significantly correlated with Margalef richness index, Simpson dominance index, Shannon-Weiner diversity index and species richness （P<0.05）, while ecosystem multifunctionality showed a non-significant correlation with Pielou evenness index. Multi-threshold method demonstrated that species richness drove the ecosystem multifunctionality within the thresholds of 1%-84% and 5%-82% inside and outside the fence effectively, respectively, and the maximum effect values were 0.69 and 0.70, respectively. In conclusion, plant diversity might alter under fence closure, which in turn affected ecosystem multifunctionality. Thus, the protection of species diversity is important for the maintenance of ecosystem multifunctionality in alpine ecosystems.

Key words: Ecosystem multifunctionality, Plant diversity, Alpine grassland in northern Xizang, Grazing exclusion and free grazing, Mean value method, Multi-threshold method