Regulation Principle And Technique Of Photosynthesis Of Cucumber Under Suboptimal Temperature And Suboptimal Light

Responses of net photosynthesis rate (Pn) of two cucumber varieties (Jinyou No.1, a greenhouse variety and Jinyan No.4, an open-land variety) to carbon dioxide (CO₂) concentration (Cr), photon flux density (PFD) and temperature (Ta) were modeled by mathematic methods. Based on the models, effects of suboptimal temperature and suboptimal light on Pn and the physiological mechanism were studied by using phytotron. Regulation techniques to improve Pn and light utilization efficiency of greenhouse cucumber under this condition were studied then. Regulations of nitrogen levels on the quality of grafted cucumber and self-rooted cucumber were also studied. The main results were as follow:1 Greenhouse cucumbers, especially the leaves of the middle-part and underlayers of the canopy, were often in suboptimal temperature (about 18℃) and suboptimal light (200～400μmol·m^-2·s^-1) in winter and earlier spring in north China.2 Pn of the two varieties were measured under given environment (Cr, PFD, Ta and relative humidity(RH), et al.) in phytotron. Then the responses of Pn to Cr, PFD and Ta were modeled by mathematic methods. The models were:Jinyou No.1:y=exp(-242.1217/x1)*(61.0202-0.1100(x2-30.9260)^2*exp(-272.8874/x3)+0.9355;Jinyan No.4:y=exp(-179.8803/x1)* (50.0771-0.0609 (x2-34.3455) ^2*exp(-267.9653/x3)+0.7377(in the equations, x1,x2 and x3 represented values of CO₂ concentration, temperature andillumination intensity respectively and y was value of Pn).From the models, we can see that the response of Pn to Ta accorded with conic, while its responses to Cr and PFD accorded with exponential function.3 The carboxylation efficiency (CE), light compensation point (LCP), CO₂ compensation point (CCP), and dark respiration rate (Rd) of cucumber leaves decreased evidently during suboptimal temperature and light treatment, apparent quantum yield (AQY) decreased at first then increased. Comparing with those of Jinyan No.4, LCP and Rd of Jinyou No.1 were lower, AQY and CE were higher, indicated that JinyouNo.1 had better adaptability to suboptimal temperature and light. The leaf area and stalk diameter of cucumber minished, while the...