Characteristics of Plant Communities and Element Contents in Plants at Mengentaoligai Ag, Pb, Zn Mine area in Inner Mongolia Preliminary Studies on the Phytocommunity of Davidia involucrata in Omei Mountain of Sichuan The Phytocommunity and Phyto-geochemistry Characteristics of Pb and Zn in the Mining Area of Xitieshan Mountain in Qinghai Province and Their Relationship with the Pb and Zn Deposits