Effect of Potassium Nitrate on Chilling Resistance and Green Period of Eremochloa ophiuroides(Munro.) Hack Effects of Infection with Botryosphaeria dothidea on Cell Membrane Permeability, Soluble Sugar and MDA Content in Poplar Calli The Preliminary Research on the Morphological and Physiological Responseto Heat Stress of Lilium longiflorum Seedlings