基金This research was supported by the National Natural Sciences Foundation of China (NSFC-30970327, 31272271, 31272272, 31301861), the National Special Fund on Basic Research of Science and Technology of China (No. 2014FY110100), the Hunan Provincial Program for Development of Key Disciplines in Ecology (No. 0713), Hunan Provincial Natural Science Foundation of China (No. 11JJ1004/12JJ3028), Program for New Century Excellent Talents in University (NCET-12-0717), China Postdoctoral Science Foundation (No. 20100471221/201104506), and the program of Hunan Provincial Science and Technology Plans (No. 2010RS4006)Acknowledgements This research was supported by the National Natural Sciences Foundation of China (NSFC - 30970327, 31272271, 31272272, 31301861), the National Special Fund on Basic Research of Science and Technology of China (No, 2014FY110100), the Hunan Provincial Program for Development of Key Disciplines in Ecology (No. 0713), Hunan Provincial Natural Science Foundation of China (No. 11JJ1004/12JJ3028), Program for New Century Excellent Talents in University (NCET-12-0717), China Postdoctoral Science Foundation (No. 20100471221/201104506), and the program of Hunan Provincial Science and Technology Plans (No. 2010RS4006).