Effects of Suboptimal Temperature and Photo Flux Density Treatment on Growth,Photosynthetic Characteristics and Nitrogen Content of Cucumber(Cucumis sativus L.) Seedlings

[Objective] The purpose was to study the effects of suboptimal temperature and photo flux density treatment on growth,photosynthetic characteristics and nitrogen content of cucumber seedlings,and discuss its effects mechanism on growth and photosynthetic apparatus of cucumber and plants' adaptive mechanism to adversity of suboptimal temperature and photo flux density.[Method] The suboptimal temperature and photo flux density was 18/12 ℃ and(200±20) μmol/(m2·s) respectively,and cucumber seedlings were treated in 5 and 10 days under this condition.[Result] The results showed that growth of cucumber seedlings were significantly inhibited,and the biomass accumulation and leaf nitrogen content were reduced by suboptimal temperature and photo flux density stress,but no influence on nitrogen content in cucumber roots;the content of chlorophyll a and b were increased after 5 d stress and then decreased for 10 d stress.The decline of net photosynthesis of cucumber seedlings under suboptimal temperature and PFD stress for 5 d were caused primarily by stomatal limitation,and the decline for 10 d were caused mainly by non-stomatal limitation.[Conclusion] The study provides a theoretical basis for finding out effective measures on controlling suboptimal temperature and photo flux density environment to guide greenhouse cucumber production in winter and spring.