It was studied the effect of
soil water content on the leaf water content and the physiological function under different
irrigation levels. It indicated that the
soil water content(SWC) had negative relation to the leaf water content(LWC) from returning green stage to enveloping the row stage, and it reached significant difference level between SWC from 20 to 40 cm and LWC. The SWC had positive relation to the LWC from flag leaf appearance to the dough stage, and it reached significant difference level between SWC from 0 to 20 cm and LWC. The leaf temperature (Tl)under the middle level water content was the lowest, the Tl improved
significantly under dry conditions, and it also had heighten tendency under the water over-saturation level. It decreased significantly the value of the changeable fluorescence(Fv) to the maximum fluorescence(Fm) of PSⅡunder water deficiency conditions at booting stage, but it had no significant influence under the water over-saturation condition. It decreased significantly the value of Fv to Fm of PSⅡunder water deficiency and the water over saturation condition at the grain filling stage. It was an important turning point of the leaf photosynthesis and physiological activity when the leaf water content dropped from 75 percent to 70 percent, and it should be done as the important reference for judging the leaf water content threshold value.