Spatial Variation Of Soil Enzyme Activity In Eastern Qinghai-Tibet Plateau——Effects Of Fertilization And Grazing

Soil enzyme system plays a key role in the soil biochemical process and is closely related to the cycle of mass and energy fluxes. Soil enzyme activity is characterized by the level of metabolism in soil, it’s the main indicator of soil fertility. We carried out a series of original observations and control experiments in the Gannan prefecture, eastern Qinghai-Tibet Plateau:4different types of grassland (alpine meadow, alpine shrub, swamp meadow, desert steppe) were selected as the research object to analyze the variation of soil physicochemical characteristics, soil enzyme activity and the inter-relationship among them; changes of soil enzyme activity at different grazing intensities and the seasonal fluctuation in the swamp meadow were studied; we studied the effects of grazing intensity and fertilization gradient on soil enzyme activity of alpine meadow, try to test the function of soil ecosystem and their potential mechanisms by way of the response of soil enzyme to environmental changes, to explore the mechanisms of soil degradation and in order to provide a theoretical basis for the sustainable development of grassland ecosystems. Our main objectives are as follows:1-soil enzyme activities at upper soil layer (0-15cm) were higher than those at the lower layer (15-30cm), and the trend was closely same between4types of grasslands, soil β-glucosidase activity in4different types of grassland was swamp meadow> alpine shrub> alpine meadow> desert steppe, acid phosphatase activity was swamp meadow> alpine meadow> alpine shrub> desert steppe, urease activity at upper soil layer was swamp meadow> alpine shrub> desert steppe> alpine meadow, at lower soil layer was desert steppe> swap meadow> alpine shrub> alpine meadow. Correlation analysis indicated that soil (3-glucosidase activity and acid phosphatase activity had significant positive correlation with soil organic carbon and total nitrogen, which can be used as indicators of soil fertility.2^We found that β-glucosidase and acid phosphatase activity decreased gradually during growth season in swamp meadow soil; β-glucosidase and acid phosphatase activity at upper soil layer decreased gradually with the intensity of grazing, indicate that grazing induced a certain extent of damage in swamp meadow soil; changes of urease activity is irregular with the intensity of grazing and the seasons; the interaction of grazing intensity and seasonal variation on swamp soil is generally not significant; there is a significant positive correlation between soil moisture and β-glucosidase, acid phosphatase and urease activity, which indicate that soil moisture is the main influencing factor of soil biochemical process on swamp meadow; there is a significant positive correlation between β-glucosidase, acid phosphatase and urease activity.3、 β-glucosidase and acid phosphatase activity on alpine meadow reached their peaks at the fertilizing gradient of60g/m2(nitrogen:12.7g/m2; phosphorus:14.1g/m2), which is the optimal condition of decomposition of organic carbon and phosphorus; β-glucosidase activity increased after the fertilization while acid phosphatase activity is lower after fertilization, which explain that fertilization can promote the decomposition of organic carbon but inhibit the decomposition of organic phosphorus; urease activity changes irregularly with fertilization gradient.4、 Acid phosphatase and urease activity decreased with the intensity of grazing on alpine meadow; all three enzyme activities reached its peak at fencing area, which indicate pasturing prohibition can maintain and improve the soil fertility of the alpine meadow ecosystem.