Effect On Physiological And Biochemical Mechanism Of Different Fall Dormancay Alfalfa Under High CO₂Concentration

The atmospheric concentration of CO2increased year by year, which will has deeply impact on plant growth, atmospheric environment, social and economic aspects, which is expected will reach to500-970μ mol.mol-1from375μ mol.mol-1by the end of this century Alfalfa (Medicago sativa) is a kind of high quality forage which widely planted around the world and had a high impact on the development of grass industry. In this experiment, we choosed three alfalfa of American standard fall dormancy control variety:Maverick (FD1), ABI700(FD6), UC-1465(FD11) as experimental materials, aimd to explore the change of photosynthesis, dry matter accumulation, the ecological structureand explore the mechanism in response in the different growth period when the concentration of CO2increased to550μ mol.mol-1and700μ mol.mol-1, the main conclusions obtained are as follows:1. Elevated CO2can greatly increased germination rate, germination potential and germination index, shorten mean germination time of alfalfa (P<0.01). The germination rate increased by about121.00-126.00%; germination potential increased by about113.00-127.00%; germination index increased about129.00-146.00%; the average germination days shortened about0.12-0.23d of alfalfa under the high concentration of CO2treatment. The treatment of550μ mol.mol-1had more ideal effect. FD11had higher germination rate and more tidy, faster under the high concentration of CO2treatment.2. The high concentration of CO2promoted the the entire growth period3.255.75d in advance of three types fall dormancy alfalfa, in addition, which extended the flowering period is about0-0.5d of alfalfa. The higher the concentration of CO2, plant fresh weight, dry weight per plant was higher of three kinds of alfalfa. The plant fresh weight increased by an average of about19.97-32.56%; the average dry weight per plant increased by about29.33-64.04%with high CO2concentration treatment. In addition, CO2concentration had significant positive effect on the plant height and leaf area of alfalfa (P＜0.05), no significant effect on stem diameter (P>0.05). In general, the higher the concentration of CO2, the growth period would reach earlier, also he higher the concentration of CO2,the bigger leaf area, plant height,and the higher the yield. FD11grew fastest, which had bigger leaf area, plant height and yield higher,had most early growth period after flowering stage.3.The treatment of high concentration of CO2can significantly promote the photosynthetic rate of net photosynthesis of Alfalfa increased Pn throughout the whole growth period of (P<0.01), the higher the concentration of CO?, the higher net photosynthetic rate of Alfalfa. The treatment of high concentration of CO2can greatly improve the alfalfa PSI1reaction center opening ratio, improve the photoelectron transfer ratio of alfalfa, improve the efficiency of the photochemical reaction of non photochemical quenching; reduce the arc protection coefficient of alfalfa, alfalfa photosynthesis, net photosynthetic rate increased in short term (about75d). Alfalfa will occur "photosynthetic adaptation phenomenon in long term (about75-145d), the photosynthetic system of alfalfa will be inhibited, the net photosynthetic rate decreased. During the initial period, the effect of concentration of CO2is more obvious, photosynthetic of FD11and FD6is stronger under high CO2concentration treatment.4. The higher concentration of CO2in the whole growth period, the larger leaf thickness, alfalfa epidermis thickness, palisade tissue thickness, spongy tissue, and the compactness and porosity had no obvious change. Each index of FD1thickening grew faster before early flowering stage, each index of FD11thickening grew faster after early flowering stage. Before the flowering period, stomatal density of leaves of alfalfa is lower with the increase of CO2concentration; After flowering period, there was no significant differences in stomatal density of fall Dormancy Alfalfa between the treatment group and the control group, and the stomatal density had being increased. Secondly, the higher the concentration of CO2, the lower stomatal conductance PCI potential of alfalfa. The concentration of CO2had impact on stomatal opening effect significantly (P<0.05), stomatal opening has been in a dynamic change, stomatal opening maximum decreased by24.79%-28.31%in maturity period when the concentration of CO2increased.6. The higher the concentration of CO2, the higher content of chlorophyll, soluble sugar, auxin, gibberellins of alfalfa. In addition, higher concentration of CO2can reduce the MDA content and abscisic acid content of alfalfa. Meanwhile, the treatment of elevated CO2concentration could suppresse the proline (Pro) content expect the flowering stage. The treatment of elevated CO2concentration had great influence on the physiological indexes in the early growth stage and flowering stage.However, there was no obvious difference between the different fall dormancy alfalfa.