Abstract: The effect of soil drought on osmotic adjustment and photosynthesis of winter wheat leaves was reported in this paper. In stressed plants, leaf water potential, relative water content, osmotic potential at full turgor, photosynthetic rate, transpiration rate and stomatal conductance decreased only after the soil relative water content fell below the critical level(40%). The degree of osmotic adjustment was 0.5 MPa in wheat flag leaf. The adjustment ability declined with lowering of leaves in position. The osmotic potential value in stressed leaves significantly dropped due to drought(from -1.23 MPa at full turgor to -2.33 MPa at zero turgor), but that of control leaves decreased from -1.23MPa to -1.61 MPa. Modulus of elasticity for the stressed plants increased from 5.74 MPa to 6.35 MPa, Under moderate and serious soil drought photosynthetic rate, stomatal conductance, relative stomatal limitation to photosynthesis and oxygen evolution in leaf blades declined, but intercellular CO₂concentration increased. The results showed that decrease in photosynthetic rate is mainly due to nonstomatal factor.

Key words: Soil drought, Osmotic adjustment, Stomatal factor, Nonsto-matal factor