National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [31172142]; Graduate's Scientific Research Foundation of Central South University of Forestry and Technology [2009bx02, 2009sx01]; Hunan Provincial Innovation Foundation For Postgraduate [CX2011B314, CX2011B315]; Beibuwan Key Project of Guangxi Natural Science Foundation [2010GXNSFE013004]