Effects Of Carbohydrates Reserves And Consumption On The Submergence Tolerance Of Cynodon Dactylon And Hemarthria Altissima

Since the operation of the Three Gorges Dam,its scheduling scheme leaded to a 30 meters' hydro-fluctuation belt in riparian zone.The original terrestrial ecosystem evolved to a wetland ecosystem which was submerged in winter and exposed in summer.Anti-season and long-time submergence made most plants gradually disappeare in original riparian zone.The ecological environment of the Three Gorges Reservoir Region was severely affected.When plants in the Three Gorges Reservoir Region were submerged,they would suffer low oxygen,low light and low CO2 stresses.Plants can change respiratory metabolism,elongate to out of the water surface to against hypoxia stress.But low light and low CO2 environment severely hampered photosynthesis underwater.Plants can't normally accumulate carbohydrates for plant physiological needs.For those plants which can not grow out of water surface,carbohydrates reserves and consumption are important for their survival during submergence period,because these decide whether those plants can successfully live through submergence period.The purpose of this study is to determine whether plant submergence tolerance is relevant with carbohydrates reserves and consumption characteristics,and then we can get a further interpretation of the mechanism why flooding-tolerant species can tolerate submergence.In order to define whether plant submergence tolerance is related to carbohydrates reserves and consumption characteristics,we selected Cynodon dactylon and Hemarthria altissima,which have different submergence tolerance as the research objects.All experiment treatments were in dark environment,and we set up completely submergence and non-submergence two treatments,30,60,90,120,150,180,210,240 days eight time gradients.We studied two kinds of plants' survival,growth dynamics and carbohydrates consumption and so on.The results are as follows.(1)The carbohydrates reserves before submergence in plants provide Material basis for plants during submergence period.Cynodon dactylon and Hemarthria altissima's stems are the parts which have the highest concentration of carbohydrates.Before submergence,there was no significant difference between the concentrations of carbohydrates in leaves between Cynodon dactylon and Hemarthria altissima.Cynodon dactylon's carbohydrates concentrations in stems,belowground parts and the whole plants are more than Hemarthria altissima's,respectively.Compared with Hemarthria altissima,Cynodon dactylon have more carbohydrate reserves that can provide more energy for plants' respiration and growth underwater.(2)Submergence inhibits plants' elongation.The rate of newly produced leaves and stem segments of Cynodon dactylon and Hemarthria altissima under non-submergence conditions are higher than those under submergence conditions respectively.The biomass of new tissues of Cynodon dactylon and Hemarthria altissima under non-submergence conditions are also higher than that under submergence conditions.Under submergence environment,plants suffered hypoxia stress,so carbohydrates utilization efficiency reduced,the energy for plants' growth also reduced.Plants' growth weakened so that the consumption of carbohydrates reduced,prolonged the survival time under experiment treatments.(3)Carbohydrates consumption rates affect plants' submergence tolerance.Cynodon dactylon's carbohydrates consumption rate is lower than Hemarthria altissima's,suggests that Cynodon dactylon has the characteristics of slow consumption from the genetic traits.Compared with Hemarthria altissima,Cnodon dactylon produced fewer new tissues,also the original leaves and new tissues' faster death cause fewer carbohydrates consumption.After 240 days' submergence treatment,the residual rate of carbohydrates concentration in Cynodon dactylon was 48.39% and the residual rate of carbohydrates concentration in Hemarthria altissima was 28.43%.Cynodon dactylon's high residual rate of carbohydrates concentration ensured plants survive longer underwater,which reflects the stronger submergence tolerance than Hemarthria altissima.(4)After same time treatment,Cynodon dactylon and Hemarthria altissima's survival rates under submergence conditions were significantly higher than that under non-submergence conditions,and Cynodon dactylon's survival rate was higher than Hemarthria altissima's when under the same conditions.After 240 days' submergence treatment,Cynodon dactylon's survival rate was 100%,Hemarthria altissima's survival rate was 96.7%.Cynodon dactylon and Hemarthria altissima began to die after 90 days' treatment under non-submergence conditions.After 150 days' non-submergence treatment,all the Hemarthria altissima plants were all dead,but there were 21% Cynodon dactylon plants still alive after 240 days' non-submergence treatment.The mainly factor that caused Cynodon dactylon and Hemarthria altissima's death was because the available carbohydrates in plants have run out.(5)Submergence didn't affect Cynodon dactylon and Hemarthria altissima's carbohydrate utilization in leaves and stems of Cynodon dactylon and Hemarthria altissima' are the same.Two species' different submergence tolerance were mostly affected by the carbohydrates reserves and consumption characteristics.