Study on the water physio-ecological characteristics of Populus beijingensis Biochemical compositions in rhizospheric soil of Robinia pseudoacacia and Sophora japonica and their influence on nutrition or associated poplar Study on the Control Index of Dothiorella gregaria Canker of Poplar Effects of Infection with Botryosphaeria dothidea on Cell Membrane Permeability, Soluble Sugar and MDA Content in Poplar Calli