Effects Of Light Intensity,Temperature,CO₂ And Water On The Photosynthesis Of Zanhuang-Jujube

Photosynthesis is the basis of crop yield. But the photosynthesis is not efficiency because of many internal and external factors. It's necessary to study the effects of ecological factors on the photosynthesis in fruit trees in order to improve the yield and quality.In this paper, these factors affecting the photosynthetic rates (Pn) of Zanhuang-jujube leaves were investigated. The Pn values of Zanhuang-jujube were measured in an open gas analysis system of CI-301PS under controlled ecological factors in leaf chamber. The target leaves were attached. And the diurnal variations of the whole season in photosynthesis of Zanhuang-jujube were also investigated. The main results were as follows:1. In clear day, after the first peak of Pn when the PAR was nearly light saturation point, the Pn values became declined. The photoinhibition may happened.2. The obvious midday depression of Pn of Zanhuang-jujube was mainly caused by the declined mesophyll photosynthetic capacity, but the high temperature> high water vapor pressure difference between leaf and air (VPD) and stomatal limitation (Ls) also contributed to it at noon.3. The Pn of Zanhuang-jujube were raised in high CO2 concentration, but the regularity of diurnal changes of Pn was not changed.4. The regularities of diurnal changes of Pn were changed as the decreased relative soil water concentration. The curves of diurnal changes of Pn became from atypical two peaks to typical two peaks and the midday depression of Pn was aggravated. Finally it became three peaks. At the same time, the concentration of chlorophyll (Chi) and the activity of root were decreased and the concentration of O2"\ MDA and the relative cell membrane conductivity were ascended with the increasing of soil water stress. It was indicated that the declined Pn of Zanhuang-jujube leaves was caused by no-stomatal factors under soil water stress.465. For clear days, diurnal changes of Pn of Zanhuang-jujube were double-peaked pattern from June to October. The first peak appeared at 8:00?10:00 AM and the Pn values were between 3.0 and 13.14 n mol CO2 ?m~2 ?s'1 .The second peak appeared at about 15:00~ 17:00 PM and the Pn values were between 1.63 and 5.90 n mol CO2 ?nv2 ?s'1 .There were obvious midday depression of Pn in June^ July and August.6. From June to October, the range of the light saturation point was from 600 to 1600 u mol ?m"2 ?s"'. The optimum temperature of photosynthesis increased with increasing light intensity; The range of the optimum temperature of photosynthesis was from 19.5 to 35.5 癈 under PAR that was 1600U mol ?nr2 ?s"1 in the growing season; Moreover, the intercellular CO2 concentration was in significant negative correlation to the daily Pn maximum; The stomatal conductance (Gs) was in significant positive correlation to the daily Pn maximum.7. From June to October, the optimum temperature of photosynthesis was in significant positive correlation to the mean maximum or minimum air temperature to which the Zanhuang-jujube plants were exposed in the previous 5^ 10> 20days.