Eco-physiological Responses Of Alfalfa Under Drought Stress And Re-watering

The development of forage industry was effected by the drought stress to a great extent for a long time. Due to climate warming, the shortage of water resources, environment deterioration and many other reasons, drought stress has become a major obstacle which has influenced the healthy and sustainable development of modern agriculture in recent years. There are many researches about the effects of the crop growth development and physiological metabolisms under drought stress, but the general varieties or period are unitary. This experiment is set with two different drought resistance of alfalfa cultivars (Golden Empress and Sanditi), divided into two periods (branching stage and flowering stage), three different water gradients:CK (Maxmun field capacity of 75%±5%), T1 (Maxmun field capacity of 45%±5%), T2 (Maxmun field capacity of 35%±5%) to compare, and the drought rchydration recovery was also studied. To study the antioxidant capacity of alfalfa under different drought condition, determination the photosynthesis, chlorophyll fluorescence parameters, the above-ground biomass, the activate oxygen metabolism, the antioxidant enzyme activities and content of antioxidant substances under different condition of drought treatment of alfalfa are conducted. The main results are as follows:1.The photosynthesis was inhibited by the drought stress, while improving water-use efficiency, and re-watering has returned to the CK level. Water stress reduced the net photosynthetic rate, intercellular carbon dioxide concentration, stomatal conductance and transpiration rate of the branching stage and flowering stage in Golden Empress and Sanditi. And with the increasing degree of stress. T2 treatment was greatly decreased than T1 treatment in the two varieties. Among the cultivars.the process value of Golden Empress was higher than that of Sanditi. WUE values show the trend of first increased and then decreased of two varieties in branching stage and flowering stage by water stress and water-use efficiency in Gold empress was greater than Suntory. After re-watering, the Pn, Ci, Gs. Tr decreased in the drought stress, and At the 7th day after re-watering, there was no significant difference between the treatments of the same variety in two stages. Among the two varieties, the Golden Empress was generally higher than Sanditi in total photosynthetic parameters. In the two period, the Pn, the Gs and Tr of flowering stage is higher than those of branching stage in the process of drought stress and re-watering among two varieties.2.The chlorophyll a, chlorophyll b and total chlorophyll content of two varieties in branching and flowering stages was reduced by the drought stress. With the time extension by re-watering, the recovery ability of Golden empress is higher than Sanditi. At the 7th day after re-watering in the two periods, the chlorophyll index of Golden empress was recovered to the CK level, but the chlorophyll index of Sanditi in T2 treatment has not fully recovered to the CK level.3.Drought stress reduced the value of the φPS Ⅱ which was in branching stage of two varieties of alfalfa, and made the T1 and T2 value less than CK in the flowering stage:at the same time, drought stress reduced the value of the Fv/Fm in branching and flowering stages of two varieties and increased the value of Fo. Fv and Fm. After re-watering, the value of the fluorescence parameters has the equal compensation or super compensation effect.4. Drought stress increased the accumulation of active oxygen, and led to membrane lipid peroxidation. Drought stress increased the content of H2O2 and the production rate of O2 . During the stress period in two varieties, the increase in Golden Empress was less than Suntory. but the re-watering recovery capability of Golden Empress is higher than that of Sanditi. At the 7th day after re-watering, two species in branching and flowering stages all returned to the CK. level. At the 7th day after re-watering in branching stage.T1< CK< T2 And after 5 days re-watering in flowering stage, the difference was not significant. Drought stress increased the relative electrolyte leakage and MDA content during the branching stage and flowering stage. During the flowering stage of Golden empress and Sanditi. T2 treatments were significantly higher than that of CK treatments. At the 7th day after re-watering, all treatments of the two varieties recovered to the CK level in different period.5.The SOD activity first increased and then decreased under drought stress of the two varieties of alfalfa in the branching and flowering stages. And the activity of POD and CAT increased gradually. At the 7th day after re-watering, the changes of SOD activity among Sanditi and Golden empress was CK< T1< T2 in branching stage, and T1<T2<CK in flowering period. Golden empress which has strong drought resistant has higher SOD activity than Sanditi which has weak drought resistant. This is similar to the change of POD and CAT. Therefore, Golden empress has the strong recovery capability than Suntory after drought stress. Compared to the two treatment period, the drought stress of mild and moderate in the flowering stage was more likely to occur overcompensation. Drought stress reduced the content of carotenoid, and increased the content of reduced glutathione, ascorbic acid and proline. After re-watering, the treatment values were obviously recovered.6. The drought stress in branching and flowering stage reduced the biomass of alfalfa leaves. But in a certain range, Golden Empress which has strong drought resistance has higher biomass, and the decline of biomass above-ground under drought stress in branching stage was greater than that in the flowering stage. After re-watering, the biomass above-ground increased. At the 7th day after re-watering, the biomass recovered to the CK level.