Study on Root Space Distribution in Soil and Nutrient Uptake in Elephant Grass and Imperial Grass Studies of Rice Straw,Elephant Grass and Hybrid Pennisetum Silage Isolation of 4-coumarate CoA Ligase Gene from Pennisetum purpureum cv.Huanan and Lignin Content Analysis of Transgenic Tobacco Plants Characters and dynamics of modular biomass and its allocation ratio in five cultivars of elephant grass