National Key Project of Scientific and Technical Supporting Program of China2012BAC01B02;National Natural Science Foundation of China31170460,31470705;the Cooperation Project with Naqu Grassland Station and Institute of Agricultural Environment and Sustainable Development in Agriculture.国家科技支撑计划2012BAC01B02;国家自然科学基金31170460,31470705;西藏那曲地区与中国农业科学院合作资助项目