Characteristic Of Soil Nutrients Of Rhizophere Soil In Different Karst Ecosystems With The Change Of Degradation Degree

The karst area in Southwest China is seriously constrained by geological settings and regarded as a seriously fragile ecological zone. The increase of people and the social and economic development have made it suffer greater and greater pressure. The conflicts between human and land are serious. Because of its fragile ecological environment, apparent conflicts between human and land, and strong activities of human, the environmental problems are getting more and more serious. Compared with the non—karst areas, soil and vegetation in the karst aeras are the impressionable natural environmental elements and have an obviously weak characteristie. it is of great importance to study soil nutrients charactristics in the process of karst rocky desertification, hence lay a precondition and theoretic base for laying out rocky desertification district, mapping out rock desertification regulation step and ecosystem restoring. The experiment was performed to understand the impact of degradation level on the rhizosphere soil nutrients in the Karst ecosystems. The rhizosphere soil was separated from the fine roots of different dominant vegetations under three different vegetation types (forest, shrubs and grassland) in Karst mountainous area from Guizhou province, and further analyzed for the nutrients pools (total and available contents). The results obtained are as follows:(1) Both total and available pool of nutrient was highest for the rhizosphere of Plotycarya longipe under forest. The P activation of Platycarya longipes in the rhizosphere under Forest was higher than others. This indicates that soil nutrients contents in the rhizosphere in karst region is mainly affected by different vegetations. the limiting factor for plant growth is available P in karst region. Plotycarya longipe would better adapt the lack of P.(2) The available pool of medium and trace element was highest for the rhizosphere of Plotycarya longipe under forest. In addition to availble Cu which was highest for the rhizosphere of Cinnamomum glanduliferum under forest. The total content of Fe and Cu were lowest for the rhizosphere under forest. Howere, available Mg and Fe Cu were highest for the rhizosphere under forest. Activation rate of Fe, Cu and Zn were highest under forest.(3) There were significantly correlation between soil organic C and total N, available N, available P, available Zn. The accumulation and transport and the supply of plant root were significant affected by soil organic C.(4) The enrichment of medium and trace elements in the rhizosphere soil of different vegetation types were different. Some of elements in the rhizosphere soil were lost. The available Fe and Cu and Zn had a higher accumulation rate. The selective absorption and growth of vegetation influence accumulation rate of elements. The size of vegetation canopy was have a direct effect on nutrient retention.(5) The available C and N and P in rhizosphere soil had a higher degree of change than the total, especially for DOC and available P. Nutrient availability showed a prompt response to vegetation degradation. However, the medium and trace elements made opposite.All in all, the vegetation succession of karst ecosystem affects comparatively the nutrient in rhizosphere soil. Soil nutrient content decreased with the vegetation succession, especially for the available nutrient. The nutrient cycle changed indicated that when the vegetation changed, thereby results in changes in the ecological function of karst ecosystem.