The Responses Of Soil C And N, Microbial Biomass C Or N Under Alpine Meadow Of Qinghai-Tibet Plateau To Changing In Temperature And Precipitation

The response of soil organic carbon and soil organic nitrogen to change in temperature and precipitation is crucial for the effects of climate change on the terrestrial ecosystem carbon and nitrogen cycles. In this study, alpine meadow ecosystem in Tibetan Plateau was chosen for a field experiment manipulating temperature and precipitation. The analysis of variance, the test of significance of difference were used to investigate how the soil organic carbon &nitrogen as well as microbial biomass carbon & nitrogen response to the variation of temperature and precipitation condition, the seasonal dynamics of the soil organic carbon &nitrogen as well as microbial biomass carbon & nitrogen, the relationship between the soil organic carbon & nitrogen and microbial biomass carbon & nitrogen.the main results are as follows:In the growing season before snow covering, the effect of precipitation and temperature variation to the content of soil organic carbon and nitrogen is relevant to soil depth and the interaction between precipitation and temperature. The effect of the variation of precipitation amount on soil organic carbon is not significant. While increasing temperature and no changing precipitation amount would cause a decreasing in soil organic carbon content at surface soil layer, while increasing temperature and reducing precipitation amount would cause an increasing in total soil nitrogen content at deep soil layer, while increasing temperature and on change on precipitation amount would cause a decreasing in total soil nitrogen content. Additionally, the variation of precipitation amount and temperature would not cause reduce soil microbial biomass C or N content under alpine meadows significantly, while increasing temperature and reducing precipitation amount would cause an increasing in the ratio of soil microbial biomass C at deep soil layer, while increasing temperature and increasing precipitation amount would cause an increasing in the ratio of soil microbial biomass N at deep soil layer.In the dormancy season with snow covering, the variation of temperature and precipitation amount had no significant effect to the content of soil organic carbon and total nitrogen content. While increasing temperature and increasing precipitation amount would cause an increasing the soil C:N ratio. The variation of temperature and precipitation also had no significant effect to the soil microbial biomass carbon and nitrogen content, while increasing precipitation amount and increasing temperature would cause a decreasing in the ratio of soil microbial biomass C at deep soil layer.The soil organic carbon content showed no significant difference in the growing season before snows covering and the dormancy season with snow covering, but the soil total nitrogen content increased after the dormancy season and the soil C:N decreased. The soil microbial biomass carbon content showed no significant difference in the growing season before snows covering and the dormancy season with snow covering, but the soil microbial biomass nitrogen content increased after the dormancy season and the ratio of soil microbial biomass C:N decreased. The ration soil microbial biomass C showed no significant difference in the growing season before snows covering and the dormancy season with snow covering, but the ratio of microbial biomass N decreased after the dormancy season.In the growing season before snows covering and the dormancy season with snow covering, the soil microbial biomass carbon or nitrogen content showed significantly positively correlation with the soil organic carbon and total nitrogen content; the microbial biomass carbon content was positively significantly correlated with the microbial biornass nitrogen content; the ratio soil microbial biomass C showed no significantly correlation with the ratio of microbial biomass N; the ratio of soil C:N showed no significantly correlation with the ratio of microbial biomass C:N.The results indicated that the soil organic carbon & total nitrogen content and, microbial biomass carbon & nitrogen content under alpine meadow was slightly respond to the variation of temperature and precipitation.This response in the growing season before snow covering was stronger than that in the dormancy season with snow covering. The soil organic carbon & nitrogen content and soil microbial biomass carbon & nitrogen content all had the seasonal dynamic. The soil microbial biomass carbon or nitrogen content showed significantly positively correlation with the soil organic carbon and total nitrogen content.The mechanisms of soil organic carbon & nitrogen and soil microbial biomass carbon & nitrogen responding to the variation of temperature and precipitation were complex. This study only investigated the trend of the soil organic carbon & nitrogen content and soil microbial biomass carbon & nitrogen content responding to the variation of temperature and precipitation. The mechanisms of these need further study. The variation of the temperature in this study was not enough to effect on the soil microorganisms in field. So the experiment methods should be improved and the long-term field experiment should be constructed. The mechanisms of soil microbial biomass carbon and nitrogen responding to the variation of temperature and precipitation should also be further studied.