Changes of Physiological Characteristic on Photosynthesis in Malus Seedling Leaves during Water Stress STUDY ON THE STOMATAL AND NONSTOMATAL LIMITATION DURING THE DIURNAL COURSE OF PHOTOSYNTHESIS IN SOYBEAN LEAVES The photosynthetic nonstomatal limitatoin of spur-apple yong trees under water stress Analysis of Causes of Midday Depression of Photosynthesis in Soybean Leaves