Study On The Adaption Of Two Cultivars Of Hemerocallis To High Temperature And Water Stresses

With the acceleration of global warming and urbanization,extreme droughts,extreme rainfall and other extreme weather occur frequently.In the north of China,the rainfall concentrates in summer,and impermeable underlying surface increase in cities,both of that induce the frequent occurrence of short-term heavy rainfall in summer and lead to the vulnerability of cities to flood and waterlogging disasters.Rain Water Garden is one of the green infrastructure which use natural resources such as plants,soil and other natural resources to storage and infiltration rain water under the background of sponge city construction,which plays an important role in landscape ecology and is in the state of alternation of dry and wet for a long time.Therefore,according to the landscape ecological function of Rain Water garden,the environmental characteristics of dry-wet alternation and the simultaneous occurrence of extreme weather phenomena of high temperature and drought in summer.It is of great significance to choose landscape plants which are both drought-tolerant and waterlogging-tolerant for Rain garden.Hemerocallis is rich in germplasm resources,variety,high in ornamental value and strong resistance to stress,therefore,Hemerocallis 'Lusty Lealand' and Hemerocallis 'Heal Frans' were used in this study to study the growth,physiological and biochemical changes of them under combined high temperature and high temperature drought stress,water flooding stress and drought-water flooding alternate stress were.The results were as follows:(1)Under high temperature and combined high temperature and drought stress,the biomass of 2 Hemerocallis cultivars showed an increasing trend of root/shoot ratio.Both of 2 Hemerocallis cultivars showed obvious stress symptoms in the early stage of high temperature and drought combined stress and the stress damage showed under combined stress was greater than that of high temperature stress.Under high temperature stress,no materials died,but at the end of combined stress of high temperature and drought,20%of both 2 Hemerocallis cultivars died.The contents of protein,proline and soluble sugar increased significantly.The SOD activity increased at first and then decreased,and the APX activity continued to increase,and SOD plays an important role in scavenging reactive oxygen species before APX.Under both stresses,the Pn,Gs,Tr of 2 cultivars decreased significantly.under high temperature stress,the Ci of the two cultivars decreased continuously,while the Ci increased with the decrease of Pn at 6 days of high temperature and drought combined stress.Evaluated by membership function method,the tolerance of 2 Hemerocallis cultivars under high temperature stress and combined high temperature and drought stress was as follows:Hemerocallis 'Lusty Lealand'>Hemerocallis 'Heal Frans'.(2)Treated with different depths of flooding stress,the stress symptoms of 2 Hemerocallis cultivars appeared at 15 days after surface flooding stress,after the gradual recovery,the injury symptoms appeared again.After 40 days of soil surface flooding,there was no death,but after 15 days of complete flooding,the shoot decay of the two Hemerocallis cultivars,with a fatality rate of 80%.Under flooding stress,the net photosynthetic rate,stomatal conductivity?transpiration rate?root activity decreased and chlorophyll content of 2 Hemerocallis cultivars decreased,and the decrease range of each index under complete flooding stress for 5 days was higher than that for 15 days under soil surface flooding stress.However,the content of soluble protein,proline and SOD,APX enzyme activity were increased and accumulated in varying degrees.In addition,both of Hemerocallis 'Lusty Lealand' and Hemerocallis 'Heal Frans'accumulated a large amount of ethanol dehydrogenase and lactic dehydrogenase during the stress period,and the accumulation was significantly higher than that under complete flooding stress.This indicates that 2 Hemerocallis cultivars can adapt to the short-term hypoxia environment through the synthesis of anoxic respiratory enzymes,and the ability of root anoxic respiration is weakened under the condition of complete flooding.Evaluated by membership function method,the tolerance of 2 Hemerocallis cultivars under different gradient flooding stress was as follows:Hemerocallis 'Lusty Lealand'>Hemerocallis'Heal Frans'.(3)Under four kinds of alternation of dry and wet stress,mild alternation of dry and wet could promote the growth of Hemerocallis to a certain extent.In arid environment,the activity of antioxidant enzymes was enhanced and osmotic regulators were accumulated to resist the effects of drought stress.Suitable flooding can promote the growth of plants,but the increase of flooding water level or the enhancement of drought stress will inhibit the growth of plants.