Increased atmospheric CO2 concentration and the possible alteration in structure of forest community Response of photosynthesis to water stress in four saplings from subtropical forests under elevated atmospheric CO2 concentration EFFECT OF HUMAN ACTIVITY ON 13 C/ 12 C RATIOS IN TREE RINGS OF PINUS MASSONIANA ON DINGHUSHAN Photosynthesis Characteristic of Quercus liaotungensis in Taiyue Mountain Region