Effects of grazing exclusion by fencing on soil mineral elements and plant community in alpine steppes of the northern Tibetan Plateau

Grazing exclusion by fencing is one of the common measures to recover degraded grasslands. The content of mineral elements in soils can affect individual plant growth and community succession. To evaluate the effect of grazing exclusion by fencing on soil mineral element content and plant community characteristics in alpine steppes, two sampling plots in Beila and Pubao of Bange County were selected. Plants and topsoil samples were collected from inside and outside the fences in summer from 2010 to 2013. Species diversity, aboveground biomass, and contents of soil Ca, Cu, Fe, Mg, Mn, and Zn were analyzed. The results showed that 1) Ca, Mg, and Cu contents in the soil in Beila Town decreased by 57.1%, 24.1%, and 37.4%, respectively, while the content of soil Cu in the Pubao Town significantly increased relative to open grazed plots, i.e., and increase of 25.2% due to the short-term (5～8 years) grazing exclusion (P < 0.05); however, no significant differences in soil Fe, Mn, and Zn were found between fenced and grazed sites (P > 0.05). 2) Aboveground biomass in Pubao Town increased significantly (P < 0.05) due to grazing exclusion, but no significant difference in species diversity weas observed between fenced and grazed sites (P > 0.05). 3) Results of ANCOVA showed that only soil Mg content was significantly correlated with aboveground biomass (P < 0.05), while the content of all soil mineral elements had no significant effect on plant species diversity (P > 0.05). Our findings indicated that the effects of short-term grazing exclusion by fencing on soil mineral element content and plant community in alpine steppes may be limited.