Physiological And Biochemical Adaptation Mechanisms Of Three Species Of Perennial Herbaceous Plants In The Drawdown Zone Of The Three Gorges Reservoir

Since the completion of the Three Gorges Reservoir,the vegetation structure has been degraded seriously and the plant species diversity has decreased significantly under the dual disturbance of "artificial and natural".The restoration of degraded ecosystem is urgent.A large number of facts have been proved that herbaceous plant seeds and propagates are the key to artificial restoration of degraded ecosystem.At present,there have been some reports on the adaptation mechanism of annual herbaceous plants to waterlogging or submergence stress in the Three Gorges Reservoir area,but for perennial herbaceous plants,In particular,the study of adaptation mechanism under seasonal waterlogging or submergence stress at different altitudes in the actual subsidence area is rarely reported.Therefore,three species of perennial herbaceous plants,Cynodondactylonlinn.pers.l.,Medicago falcata l.and Medicago sativa l.of the Three Gorges Reservoir were studied in this paper.The adaptation mechanism of perennial herbaceous plants to seasonal submergence stress was explored from the following two ways: 1)the adaptation mechanism of seed submergence tolerance from 2014 to 2016,and the adaptation mechanism of seed tolerance to submergence stress was studied in three perennial herbaceous hyacinth,I.e.,150 m,160m,165 m and 174 m,respectively,in different heights in the actual decaying area,in which three species of perennial herbaceous plants were studied.Alfalfa and alfalfa seeds were treated with water flooding to analyze seed viability,seed germination rate,physiological and antioxidant system related enzyme activities,so as to explore the possibility of three kinds of perennial herbaceous seeds for artificial restoration in the decaying area.2)the adaptation mechanism of the breeding body to water flooding stress,mainly aimed at the perennial herbaceous plants with poor adaptability to submergence stress,2013-2015,and taking the representative perennial herbaceous Cynodondactylonlinn.pers.L as the experimental object,in the 150 m height of the actual declining area.Through sowing seeds in the mature stage to form a propagator,and then to construct adaptive plants with different times of seasonal flooding(different years of adaptation,the following with the same number of years),and the growth related indexes of different years of adaptation of Cynodondactylonlinn.pers.L.The accumulation and distribution patterns of unstructured carbohydrates were analyzed to understand the adaptation mechanism of the vegetative bodies of the submergence tolerant plant to the seasonal submergence stress.The results show that:1)After three species of perennial herbaceous seeds were subjected to submergence stress at different elevation,in general,the seed viability of submerged seeds in the middle area of the water-level-fluctuation,160 m and 165 m,were highly in three species,respectively,but the viability of submerged seeds decreased significantly near the waterline,174 m,and the down area,150 m.2)The seed germination rate of three perennial herbaceous seeds,only Medicago falcata L.could germinated at 174 mg 165m elevation,12.00 ±2.08 and 4.33±1.45% ±1.45 m,respectively,after water submergence.Although Cynodondactylonlinn.pers.L.and Medicago sativa L.could keep highly seed viability and non-significant difference compared with the control,but after a long period of submergence stress,the germination ability was lost.3)The content of soluble sugar and soluble protein decreased significantly,while the amount of starch synthesis increased.The storage resources of seeds was accelerated consumption by low efficiency anaerobic respiration under submergence stress,the increase of starch content may be reserve the direct utilization of carbohydrates for seed germination and seedling establishment.4)The seeds of three perennial herbaceous plants can induced to increase the activity of antioxidant related enzymes by submergence stress at different elevation,thus avoiding the damage caused by reactive oxygen species.5)In 50 d recovery,the height and longest leaf length of the different adaptation plant were lower than that grown in normal condition.During the recovery period,limited resources were used for leaf building to rapidly accumulate photoassimilate,rather than for plant elongation.6)After seasonal submergence stress in the water-level-fluctuation zone,there were significant differences in the allocation patterns of non-structural carbohydrates between the adaptation plants and the control plants(without flooding): the storage patterns of non-structural carbohydrates tended to stolon in the adaptation plants of different years.The non-structural carbohydrate storage of the control plants tended to the root.7)The non-structural carbohydrate accumulation of multi-year adaptive plants(local plant of Shaiwangba)was significantly higher than that of two-year,three-year old and control plants.In totally,the results suggested that the perennial herbaceous Medicago falcata L.seeds can endure submergence stress at 165 m and 174 m,and germinate,which can be used to construct vegetation in the Three Gorges Reservoir.The adaptability of Cynodondactylonlinn.pers.L.and Medicago sativa L.seeds to submergence stress is poor.How to use the seeds for ecological restoration in the decaying area should be further explored.Through the change of accumulation and distribution strategies of non-structural carbohydrates,it may be one of adaptive strategies of Cynodondactylonlinn.pers.L.for endure the seasonal submergence of the Three Gorges Reservoir.