Effects of exclosure on plant and soil nutrients in an alpine grassland

Exclosure is among the most common measures applied to restore degraded alpine grasslands on the Qinghai-Tibetan Plateau. The study aimed to examine the effects of exclosure on soil physicochemical properties and plant nutrient contents and to evaluate the impact of exclosure on grassland restoration based on the relationship between soil properties and plant nutrient content. In this study, three pairs of grazed and fenced plots that had been enclosed for 6, 11, and 12 years were selected in Bange County, Nagchu City, Tibetan Autonomous Region, China. The results showed that 1) exclosure significantly increased aboveground biomass and vegetation coverage (P < 0.05) but significantly decreased the Shannon-Wiener diversity index and Margalef richness index (P < 0.05); 2) no significant differences existed between bulk density, total carbon (TC), and total nitrogen (TN) of soils at different depths within and outside of fences (P > 0.05); 3) the effects of exclosure on the relative importance of plants varied with species, and significant differences in TC, TN, and nitrogen-use efficiency (NUE) existed among species (P < 0.05); and 4) the correlation between vegetation and the primary nutrient content of topsoil only existed between some species and some nutrients. The results indicated that exclosure could significantly change vegetation productivity and community composition but had relatively little effect on soil properties and plant nutrient utilization. Therefore, the restorative effects of exclosure on degraded alpine grassland ecosystems on the Qinghai-Tibetan Plateau require further and more comprehensive investigation.