Photosynthesis adaptation of cucumber seedlings to suboptimal temperature and low light intensity stress

In order to determine the mechanism of photosynthesis adaptation to adverse temperature and light intensity for cucumber seedlings, the effects of low light, suboptimal temperature, suboptimal temperature and low light stress on photosynthesis of cucumber seedlings were investigated with Jinyou 3 as material. The results showed that low light, suboptimal temperature, suboptimal temperature and low light stress all led to decrease in net photosynthetic rate(Pn) and RuBP carboxylase activity remarkably. Decrease in Pn under the stress condition was mainly attributed to non-stomatal limitation, besides the treatments under suboptimal temperature, suboptimal temperature and low light intensity, which had something to do with stomatal limitation. Temperature plays a primary role when suboptimal temperature and low light intensity appear simultaneously. The light compensation point decreased during ten-day low light or suboptimal temperature and low light stress. Low light or suboptimal temperature and low light stress caused decrease in actual photochemical efficiency of PSⅡ(ΦPSⅡ) and initial fluorescence(Fo), little changes in maximal photochemical efficiency of PSⅡ in darkness(Fv/Fm). Suboptimal temperature led to decrease in ΦPSⅡ and Fv/Fm, but no significant changes in Fo. This result suggested that no photo-inhibition occurred under low light or suboptimal temperature and low light intensity stress, suboptimal temperature was likely to induce PSⅡ photo-inhibition, but no significant injury to PSⅡ reaction center occurred.