摘要
Alpine grassland desertification is an important environmental problem, which have an important impact on grassland forage production and residents' living environment. The current studies on grassland desertification are mostly focused on the changes in vegetation and soil properties during desertification process, with no prior knowledge about which variables are more sensitive and can be used to indicate state transition in the desertification process, and how to quantify the ecological threshold of the desertification process. Using the method of space- for- time, five types of communities were selected to represent the different gradients of alpine grassland desertification to systematically study the changes in plants, soil properties, and microorganisms during the desertification process, and to identify the desertification thresholds. The results showed that plant community cover, above- ground, and underground biomass significantly decreased with the increase in desertification. Soil moisture concentration gradually decreased, and soil bulk density gradually increased with the increase in the extent of desertification. Gravel content was significantly higher in severely desertified grassland community than in other desertified community types. Soil total carbon and nitrogen concentrations in the soil surface (0-10 cm) gradually decreased, and the ratio of carbon to nitrogen was significantly higher in severely desertified community than in other types of grassland community. Abrupt changes in vegetation occurred in lightly to moderately desertified communities. Meanwhile, rapid changes in soil properties and soil microorganisms (desertification threshold) occurred in moderately to severely desertified communities. Such results suggest that the response of plants to desertification could be more sensitive than that of soil sub-systems, and plants could be treated as a more direct indicators of the gradients of grassland desertification. Moreover, mildly to moderately desertified communities could be the key stage of grassland desertification. Thus, it is very important to take the right methods to avoid further desertification of the grassland.
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