Soil Enzymatic Activity In Different Grassland Types On The Western Slopes Of The Helan Mountains, China

Soil enzymatic activity is one of the most important indexes of biological activities in the grassland ecosystem. In this study, we conducted different grassland types at different altitudes along Helan mountain range, in Alxa, Inner Mongolia, China. On the basis of field investigation and laboratory analysis, we studied the distribution characteristics of soil urease, saccharase, alkaline phosphatase and catalase activities among the different grassland types. Furthermore, the relationship between soil enzymatic activities and soil properties, vegetation characteristics, and climatic factors, and the effects of seasonal change and exclosure practice on soil enzymatic activities were investigated in this paper. The results of this study are shown as follows:(1) The soil enzymatic activities declines with decreasing altitude and followed by the order: alpine meadow> mountainous steppe> desert steppe> steppe desert, which is significantly different in the 0-10cm layer. The variation ranges of soil urease, saccharase, alkaline phosphatase and catalase activities among different grassland types are in 0.01-0.37 mg NH₄-N g^-1 soil. 3h^-1,3.90-99.29 mg glucose g^-1 soil 24h^-1,0.04-1.48 mg P. g^-1 soil 12h^-1 and 1.44-5.66 ml KMnO₄. g^-1 soil, respectively. The soil enzymatic activities are gradually reduced following the soil vertical section.(2) The four kinds of soil enzymatic activities were all correlated with annual average temperature, rainfall, plant cover, plant productivity, soil microbial biomass carbon and nitrogen, organic carbon content, total nitrogen, water content, pH. Soil enzymatic activities preferably reflect the soil and vegetation conditions. They can be used as the biological indicators of the grassland degradation degree in the study region. Stepwise regression analysis showed that soil microbial biomass carbon and rainfall were the key factors affecting soil enzymatic activities in the study region.(3) Results showed that it was significantly different among the four kinds of soil enzymatic activities in mountainous steppe, desert steppe and steppe desert. Soil urease activity probably was more sensitive to temperature fluctuation, and it reached the highest in July; Soil saccharase activity continuously went up from April to September, and it reached the highest at the time of good hydrothermal condition in September. Soil alkaline phosphatase and catalase activities showed a decreasing trend in mountainous steppe, but an increasing trend in steppe desert.(4) Soil urease was obviously affected by grazing and exclosure. By exclosure practice for 5 years, soil urease activity has increased by 22.5% at mountainous steppe. So soil urease maybe used as a sensitive indicator of the soil rescovery about degenerated grassland. Comparatively, the effects of grazing and exclosure on soil alkaline phosphatase and catalase were not obvious in this study.