Ecological Effect of Phytoremediation on Oil Shale Waste Dumps SEASONAL CHANGES OF PHOTOSYNTHETIC CHARACTERISTICS IN 12 TREE SPECIES INTRODUCED ONTO OIL SHALE WASTE The soil and vegetation of oil shale dump in Maoming city, Guangdong Province Ecological restoration of oil shale waste dumps Responses of Photosynthesis in Two Woody Plants to Oil Shale Residue Pollution Differences in Photosynthesis and Plant Growth of 26 Woody Species at the Oil Shale Waste Dump Stomatal Gas Exchange in Leaves of Major Trees on the Oil Shale Residue in Maoming, Guangdong