Response of the plant community and soil water status to alpine Kobresia meadow degradation gradients on the Qinghai-Tibetan Plateau, China

Degradation of alpine Kobresia meadow in the Qinghai-Tibetan Plateau is a serious problem, but its effect on the plant community and soil water status is not fully understood. We chose four homogeneous sites with < 20, 20-70, 70-90, and > 90 % absolute abundance of palatable grasses, and classified them as degradation gradient categories of poor, fair, good, and excellent, respectively. The lowest aboveground biomass and infiltration rate, and the highest root biomass, thickness of mattic epipedon, topsoil (< 10 cm) organic matter content and volumetric ratio of root/soil all occurred in fair plots. There was little fluctuation in plant community diversity and topsoil bulk density among the degradation gradients. Results of non-metric multidimensional scaling suggested that vegetation dynamics along degradation processes were non-equilibrium in the alpine Kobresia meadow. The effects of degradation on soil water content and retention were the highest in the top layer (> 10 cm). The minimum topsoil water content and maximum topsoil water retention both occurred in fair plots, indicating asynchrony between soil water content and holding capacity along degradation gradients, which likely resulted in a non-equilibrium plant community pattern through physiological desiccation and nutrient deficits. Our findings should be highly informative for threshold-based management of the degraded alpine Kobresia meadow in the future.