贵州喀斯特区石漠化严重，有效养分缺乏，水稻生态系统尤其缺磷，而传统无机磷肥利用效率仅有15%-20%，面源污染严重。我们前期研究发现紫花苜蓿绿肥能够提高稻田磷素利用效率，但其微生态作用机理尚不明确。本项目选取贵州喀斯特传统稻田为研究区，引入紫花苜蓿绿肥，当地紫云英绿肥及化肥作为对照，以水稻生长过程中根际土壤-水稻的磷素循环为主线，动态监测水稻根系和地上部分磷含量、根际土壤各形态磷含量，结合土壤磷酸酯酶活性，明确水稻生态系统磷的吸收和积累对根际磷素转化进程的响应机制，并采用16S rDNA方法，鉴定根际土壤解磷细菌的种类，培养关键解磷细菌，从解磷细菌的解磷能力和方式综合探索其对水稻根际磷素的转化进程的影响，进而从根际微生态水平揭示紫花苜蓿绿肥对水稻磷利用效率的作用机制，为缓解贵州喀斯特区稻田磷缺乏和引入高效紫花苜蓿绿肥-水稻轮作体系提供理论依据。

It’s growing rocky desertification in Guizhou karst landforms, led to soil available nutrient-deprived, especially P deficiency in paddy soils. However, the utilization efficiency of traditional inorganic phosphorus is as low as 15-20%, which is exposed to non-point pollution. In our previous study, we found that alfalfa (Medicago sativa L.) is rich in nutrients, and can significantly increase phosphorus utilization efficiency as green manure from paddy, but the microecological mechanisms have not yet been researched. In this project, we choose alfalfa as green manure, Chinese milk vetch (Astragalus sinicus L.) and traditional inorganic fertilizer as controls from traditional paddy field in karst landforms. The main line is P cycling between rhizosphere soil and rice plant. We will analyze the P contents in root and above-ground biomass, and the P contents as different forms in rhizosphere soil, combined with soil phosphatase activity during the rice growing, to explicate the response of the P uptake and accumulation in rice plant to the process of P transformation in rhizosphere soil. We will use 16S rDNA to identify the species of phosphate solubilizing bacteria, and culture the key phosphate solubilizing bacteria. We will explored the mechanism of phosphate solubilizing bacteria on the P transformation, and further to reveal effects of alfalfa green manure on phosphorus utilization efficiency and rhizosphere microecological mechanisms, which will be very important to alleviate P deficiency in paddy field. It will provide the scientific basis and theoretical support for establishment of a new and efficient green manure alfalfa-rice rotation system in Guizhou karst landforms.