Effects Of CO₂ Concentration And Salt Stress On Physiological Characteristics Of Medicago Sativa Cv. Pianguan Seedlings

In recent years,atmospheric CO₂ concentration continues to increase,causing greenhouse effect,soil salinization is increasingly intensified,and affecting the growth and development of Medicago sativa.The aim of the experiment was to explore the response of Medicago sativa cv.Pianguan to CO₂ concentration and salt stress.The artificial climate incubators were used to set two CO₂ concentrations of 400 and 800 ppm.The pot experiment was used to simulate salt stress（Na Cl）.The changes of growth characteristics,photosynthetic characteristics,cell membrane permeability,osmotic adjustment substances,ion accumulation and active oxygen metabolism of Medicago sativa cv.Pianguan under different CO₂concentration（400 and 800 ppm）and Na Cl concentration（0,75,150,225,300 mmol·L-1）treatment for different days（7,14,21,28 d）were researched.The main results were as follows:（1）Salt stress inhibited the growth,seedling biomass accumulation and leaf thickness of Medicago sativa cv.Pianguan.The inhibition of salt stress was significant（P<0.05）after 28 days treatment.CO₂ concentration of 800 ppm promoted the growth and development of Medicago sativa cv.Pianguan,and enhanced the adaptability of Medicago sativa cv.Pianguan to salt stress.（2）Salt stress inhibited the photosynthesis of Medicago sativa cv.Pianguan,and reduced the photosynthetic characteristics of Medicago sativa cv.Pianguan.After 21 and 28 days treatment,salt stress significantly increased（P<0.05）the intercellular CO₂ concentration（Ci）of Medicago sativa cv.Pianguan at 400 ppm CO₂,and the Ci rised after significantly decreased（P<0.05）at 800 ppm CO₂ concentration.For the other indicators,salt stress was significantly reduced（P<0.05）after 14-28 days treatment.The 800 ppm CO₂ concentration improved water use efficiency,restored PSII photochemical activity,ensured the normal generation of photosynthetic harmonization,enhanced photosynthesis,and to a certain extent alleviated the adverse effects of salt stress on photosynthesis of Medicago sativa cv.Pianguan.（3）Salt stress improveded membrane permeability of Medicago sativa cv.Pianguan,decreased osmotic potential and accumulation of harmful ions,and salt stress was significantly decreased（P<0.05）after 21 and 28 days treatment.CO₂ concentration of 800 ppm effectively alleviated the decrease of leaf relative water content,reduced relative electrolytic leakage and malonaldehyde,and to a certain extent enhanced the water retention ability of salinized plants;It promoted synthesis of soluble sugar and soluble protein in plants under salt stress,improved the water absorption capacity of cells,reduced proline in plants,increased osmotic potential,and maintained the ion balance in Medicago sativa cv.Pianguan.（4）Salt stress improveded the accumulation of reactive oxygen species（ROS）and the enzymatic and non-enzymatic systems in Medicago sativa cv.Pianguan,and salt stress was significantly increased（P<0.05）after 28 days treatment.CO₂ concentration of 800 ppm alleviated the oxidative damage of Medicago sativa cv.Pianguan under salinity stress,reduced O₂-and H2O₂ content,and increased the content of superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）and ascorbic acid peroxidase（APX）,glutathione reductase（GR）,ascorbic acid（ASA）and glutathione（GSH）so that the salt tolerance of Medicago sativa cv.Pianguan was enhanced.In summary,the higher CO₂ concentration could increase the seedling biomass and leaf thickness of Medicago sativa cv.Pianguan under salt stress.The photosynthesis,water absorption and retention capacity,osmotic adjustment ability of Medicago sativa cv.Pianguan were enhanced.The ion balance in Medicago sativa cv.Pianguan was maintained.The accumulation of ROS in Medicago sativa cv.Pianguan was reduced,the antioxidant enzymes and antioxidants improved.The higher CO₂ concentration alleviates the damage of Medicago sativa cv.Pianguan under salt stress,and improves the salt tolerance of Medicago sativa cv.Pianguan.