Effect of short-term daytime sub-high temperature stress on photosynthesis of tomato leaves

In order to investigate the effect of short-term sub-high temperature stress on photosynthesis of tomato leaves , the authors utilized artificial climate chamber to simulate 35℃ sub-high temperature environment during the 1st inflorescence flowering, with 25℃ as control to study the effects of short-term sub-high temperature stress on diurnal changes of photosynthesis of tomato leaves. The results showed that: when tomato leaves treated with sub-high temperature at 35℃ for less than three days, it was shown that net photosynthetic rate was higher than that of control, while treated for more than six days, the net photosynthetic rate was lower than that of control in suitable illumination intensity conditions; The diurnal changes of net photosynthesis rate of tomato in suitable temperature treatment(control, 25℃) did not appear “midday depression” , while the diurnal changes of net photosynthesis rate of tomato in sub-high temperature treatment(35℃) appeared lightly “midday depression”. The sub-high temperature treatment(35℃) improved stomatal conductance, reduced stomatal limitation, improved the ratio of open stomata, increased intercellular CO2 concentration and transpiration rate. These results illustrate that: in suitable illumination intensity conditions, the tomato which suffered sub-high temperature stress for a short time can adjust some oneself reaction to adapt to environment, in order to avoid the decline of net photosynthetic rate. But when it is treated for more than six days, photosynthetic rate is affected. The “midday depression” is not just related to illumination intensity, but also related to temperature. The effects of sub-high temperature treatment on net photosynthetic rate is not related to stomatal factors, but to nonstomatal factors.