Abstract: The study on the effects of long-term suboptimal temperature (T₁) and short-term low temperature (T₂) under low light density on cucumber seedling's growth and its photosynthesis showed that the growth speed,photosynthetic rate (Pn),carboxylation efficiency (CE),apparent quantum yield (AQY) and actual quantum yield of P SⅡ electron transport (Ф_PSⅡ) all declined remarkably,and the photochemical efficiency of PSⅡ (F_v/F_m) also decreased to some extent.The decreasing extents of Pn,CE and AQY of T₁ were less than those of T₂,while the recovery rate of T₁ was slower than that of T₂.The F_v/F_m and Ф_PSⅡ of T₁ declined to less extent and resiled quickly,while those of T₂ decreased to larger extent and recovered slowly.The contents of chlorophyll a,chlorophyll b and carotenoid of T₁ increased remarkably after being treated,while those of T₂ decreased evidently.The Chl a/b of both T₁ and T₂ declined remarkably.With recovery time going,the pigment of T₁ declined under most conditions,while that of T₂ increased gradually.Three days later,the pigment content of T₁ and T₂ were both higher than control.The Chl a/b had no significant change during the recovery period,and was still obviously lower than control.

Key words: Low light density, Long-term suboptimal temperature, Short-term low temperature, Photosynthesis, Growth speed, Cucumber