Demand For CO₂ Concentration In Different Light Intensity Of Grafting Cucumber In Greenhouse

In this experiment, grafted cucumber in greenhouse was selected as rest material to explore the changes of form, chlorophyll content, photosynthetic rate and chlorophyll fluorescence parameters under different light intensity and CO2 concentration in order to provided theoretical basis for high yield and quality cultivation of grafting cucumber. The results show that:1. The plant height and leaf area of cucumber both were the largest with medium concentration CO2 under full light and relative 32% light. The Stem diameter was the largest with high concentration CO2 under full light.2. The chla, chlb, chl (a+b) of cucumber leaf were the largest with high concentration CO2 under full light and with medium concentration CO2 under relative 32% light.3. The Gs and Tr of cucumber leaf both were the least with high concentration CO2 under full light and relative 32% light. The Ci of cucumber leaf was the least with high concentration CO2 under three kinds of light intensity.4. The Fv/Fm, qP, ETR of cucumber leaf were the largest with high concentration CO2 under full light and relative 15% light. And they were the largest with medium concentration CO2 under relative 32% light. The NPQ of cucumber leaf was the least with high concentration CO2 under three kinds of light intensity.5. Comparing all treatment, the treatment of full light+high concentration CO2. has the largest daily average of Pn and ETR. The treatment of relative 32% light+ medium concentration CO2 has the largest daily average of Fv/Fm and qP, and daily average of NPQ was least, long-time average of Pn. Thus these two treatmen combination were the optimal combination of light intensity and CO2 concentration.6. Over time, the plant height, leaf area, stem diameter grew slowing down, and the content of chla, chlb, chl (a+b), Pn were decreased, especially the treatments of applying high concentration of CO2 in the post-processing, and made cucumber plant premature aging.7. The peak of diumal variation curve of Pn did not change with different CO2 concentrations, so the CO2 concentrations was not the main reason for caused "midday depression" phenomenon. But the diurnal changes of Pn under no shading were double-peak curve, and the phenomenon of midday depression appeared. And under shading were unimodal curve, shows that high light intensity maybe the reason that caused "midday depression" phenomenon. Proper shade could effectively relieve the midday depression phenomenon. But severe low light could cause Pn decline.