RESPONSES OF PHOTOSYNTHESIS ON WATER STRESS FOR SHRUBS FROM TROPICAL RAIN FOREST AND SUBTROPICAL MONSOON FOREST The effect of groundwater depth on the δ13C value of constructive species leaf in the lower reaches of the Tarim River Relations between Stable Carbon Isotope Discrimination and Water Use Efficiency as well as Growth for Poplar The responses and mechanisms of water use efficiency to different water stresses of three alfalfa varieties