Research On The Soil Eanyme Activities And Soil Nutrients In The Alpine Meadow Of The Northeast Qinghai-Tibet Platcau

Qinghai-Tibet Plateau is considered as a sensitive and vulnerable area of climate change due to the high altitude and cold climate. Global climate change and grazing disturbance have strong impact on activities of soil enzyme and content of soil nutrients, which may lead to many changes in soil quality, and thus have some impacts in vegetation productivity of the alpine meadow.As an important part of soil ecosystem, soil enzyme participates in all of biochemical reactions in soil. Enzymatic reaction is a complex process controlled by many factors. Soil enzyme activities change strongly with time and space. In order to reveal the temporal and spatial variation of soil enzyme activities, the relation between soil enzyme activities and main regulating factors, and the response of soil enzyme activities to global warming, we measured soil enzyme activities. To better understand the dynamics of the soil enzyme acitvities and soil mutrients on the Qinghai-Tibet plateau, we investgated the effect of fencing and grazing on the soil enzyme acitvities, soil mutrients and root biomass at four sites with different grazing intensity in2007and2008. At the same time, we analyzed the distribution of soil enzyme acitvities and soil nutrients at three different altitudes (3000m,3500m,4000m). Also, we discused the relationship between soil enzyme acitvities and soil nutrients. The main results as follows:1. Soil enzyme activities, soil nutrients and root biomass differed significantly among four sites with different grazing intensity. The activities of acid phosphatase and amylase reduced with the increase of grazing intensity, as well as root biomass. However, the urease activity was just opposite to them. Soil enzyme activities had obvious seasonal variation. We suggest that May is the optimum sampling time for urease and acid phosphatase, as for amylase and cellulase it is in July.2. The effect of grazing on soil nutrients was not statistically significant, while light grazing markdely increased the activities of soil acid phosphatase and amylase. As measures of soil quality, the content of soil organic matter, total nitrogen and avaiable nitrogen were higher in the light grazing site, which demonstrated that light grazing promoted enrichment of the soil organic matter and N pool in the study area.3. The content of soil organic matter, total nitrogen, total phosphorus, avaiable nitrogen and soil water increased with increasing altitude, and altitude had significant impact on soil organic matter, total nitrogen, avaiable nitrogen and soil water content (P<0.05), which indicated soil quailty of higher altitude was much better.4. The activity of acid phosphatase reduced with increaseing altitude, however, the change trend of urease activity was just opposite to it, which indicated lower soil pH (5.51) and higher soil water content (73.62%) of high altitude ptomoted activity of acid phosphatase and inhibited activity of urease. The activities of amylase and cellulase were highest at altitude of3500m, which indicated soil pH (5.53) and soil water content (47.10%) at3500m were more appropriate for both.5. We analyzed the relationship between soil enzyme activities and soil nutrients by Path Analysis. The result showed that there were strong correlation between activities of urease(acid phosphatase or amylase) and soil mutrients. Therefore, the activities of urease, acid phosphatase and amylase could be used to predict the soil quality.