Abstract: This experiment dealt with the influence of CO₂ at the concentrations of 200,350,500,700 and 1000 mg/kg on photosynthetic and respiratory rates and RubisCO activity. The results showed that the CO₂ enrichment did increase the photosynthetic rate of upper leaves of cucumber, especially under intensive light conditions. The response of photosynthetic rate to the different CO₂ concentrations appeared low at the beginning, then higher and finally lower. The respiratory rates of these leaves increased rapidly with the enrichment of CO₂, until 6 min. Later all dropped to their lowest levels despite the CO₂ concentrations, from when there was no notable effect of CO₂ concentrations on the respiratory rates. The photosynthesis rate was positively correlated with the atmospheric and intercellular CO₂ concentrations. Generally the stomatal conductance was not a factor to inhibit photosynthetic at high CO₂ concentrations. The RuBP carboxylase activity was enhanced while RuBP oxygenase activity and also the ratio of the former to the latter decreased. Nevertheless,when the CO₂ concentrations were over 500mg/kg,the activity of RuBP carboxylase increased slightly.

Key words: Cucumber, CO₂ concentration, Photosynthetic rate, Respiratory rate

CLC Number: 

• S642.201