The Effects Of CO₂ Enrichment To The Physiological Characteristic Of Cucumber (Cucumis Sativus L.) Under Salt Stress

Atmospheric carbon dioxide levels CO₂ have been increased from 280 ppm to 370 ppm since industrial revolution. It will continue to increase and will probably reach 550 ppm by the end of the 21st centuary. CO₂ is the most important carbon source for plants. It has been reported that growth yield can be increased by elevating CO₂. .In recent years, with the cultivation expanded greatly in the greenhouse, the secondary salinization of the soil is becoming heavier and has become a main factor of limiting the sustainable development of vegetable production. Cucumber (Cucumis sativus L.) is an important vegetable and is widely planted in open field and greenhouse. Therefore, the research of salt tolerance in cucumber is of theoretic and practical significance to direct the production of cucumber and improve the use efficiency of greenhouse. In this experiment we studied the effects of CO₂ enrichment on the physiological and biochemical mechanisms in cucumber under salt stress in order to clarify the possible mechanisms of enhancing salt tolerance in plants. The main results were presented as follows:1.Under salt stress the growth of cucumber was inhibited, CO₂ treatment significantly increased plant leaf area and shoot fresh,dry weight, but had no significantl effect on the root. Pn was decreased by salt stress. Elavating CO₂ did not increase Pn ,even slightly decreased. Tr and Gs were decreased by salt stress, under CO₂ enrichment Tr and Gs were decreased and WUE was increased. Under 75 mM NaCl treatment quantum yield of PSII (ΦPSII) was increased. There were no obvious differences of Fv/Fm among different treatments. qP was decreased by salt stress, but did not obviously affected by CO₂ enrichment. NPQ was significantly decreased by CO₂ enrichment.2. Under salt stress, in the absence of CO₂ enrichment the content of MDA was increased, while in CO₂ enrichment the content of MDA had almost no change. POD activity was decreased by salt stress, but had no change in the condition of CO₂ enrichment. Salt stress elavated SOD and APX activity, more significantly under CO₂ enrichment. CO₂ enrichment did not improve CAT activity with or without salt stress, while salt stress increased CAT activity.3. Salt stress significantly decreased the absorption of K⁺ and increased the absorption of Na⁺, however, the effect of elevated CO₂ under salt stress was not obvious. Under CO₂ enrichment, K⁺/Na⁺ in leaves was slightly higher, while in roots, it was not consistent, but the extent of the decrease is smaller.