Effects Of Water Flooding Stress On The Distribution,Physiological And Growth Status Of The Plant Communities In The Riparian Of Le'an River

Plant community is a product of the interaction between plants and the environment.It provides the main material resources for human survival,maintaining the health and function of the Earth's ecosystem.It is the material basis for human survival and development indispensable,having irreplaceable role.Community structure is an important indicator of the community.The dominant species on the formation of community structure and community environment has a significant role in the control.(1)In riparian zone of Le'an River is the study area in this paper.Studying distribution dominant species at the riparian zone of Le'an River in different seasons.The results showed that these features as well as its possible causes and the water level of Le'An River fluctuation relations were discussed.In the study area,the spring's dominant plant is Carex cinerascens population,with Cynodondactylon and Polygonum hydropiper.In summer,Le'an River's water level rises,Carex cinerascens exit in riparian zone of Le'an River,Hemarthria sibirica become the dominant plant,because of far away from the river.Cynodondactylon is immediately followed by the species,with Polygonum hydropiper and Hydrocotyle sibthorpioides.The important value of Hemarthria sibirica declined but still is the dominant plant until the autumn.The important value of the Cynodondactylon plant is still high,and the important value of Carex cinerascens become the third.In winter,Hemarthria sibirica is the riparian zone of Le'an River dominant species,and the plants of Hemarthria sibirica disappeared from the riparian zone of Le'an River until spring.In summary,Le'an River riparian zone is closely related with the distribution of the Le'an River water level fluctuation in different dominant species,showing obvious characteristics of seasonal variation.(2)This paper aims at exploring the physiological and morphological characteristics and response mechanism of riparian plants under water flooding stress,the dominant plants such as Cynodon dactylon,Hemarthria altissima,Alternanthera Philoxeroides,Polygonum hydropiper,rumex japonicus,Nasturtium palustre were collected from riparian zone of the Le'an River and cultured indoor using soil pot methods.The water level was controlled using toughened glass tank.Different water flooding stress conditions were set up as follows: Control group(CK),infiltration(INF),half flooded(HALF)and all flooded(ALL).We measured thechanges of chlorophyll contents,photosynthetic parameters,fluorescence parameters,fluorescence imaging and morphology at different periods of water stress,and analyzed the above indexes reflected in the level of community and the resilience response mechanism of the plant groups under the water flooding stress.Under short-term water stress condition,our results shown that the degree of total chlorophyll(Chlt),net photosynthetic rate(Pn),transpiration rate(Tr),intercellular CO2 concentration(Ci),maximum quantum yield(QYmax),plant height and leaf number of each plant were decreased compared with the control group(CK).However,the average contents of Chlt,Pn and QYmax in the infiltration groups were slightly higher than those of the control group.The concentration of intercellular CO2(Ci)was elevated,while the values of non-photochemical quenching(NPQlss)was decreased first and then increased.The physiological and morphological indexes of the four plants under the long term water stress was comparable to the short term water stress.The Pn and leaf number in all flooded groups significantly decreased compared to the corresponding short term warter stress groups,Cynodon dactylon,Hemarthria altissima,Alternanthera Philoxeroides,Polygonum hydropiper w(Chlt),Pn and leaf number significantly lower than CK group(P<0.05): Cynodon dactylon:100%,100%,100%;Hemarthria altissima: 67.9%,63.8%,62.3%;Alternanthera Philoxeroides: 73.6%,83.2%,89.6%;Polygonum hydropiper: 54.5%,100%,100%;rumex japonicus:69.14%?75.69%?80.2%;Nasturtium palustre:61.33%?70.28% ? 70.0%,respectively.All plants of Cynodon dactylon and Polygonum hydropiper died in all flooded groups,suggesting that the effects of water stress under the different water levels of the four plants and the resistance of the plants to counteract the effect of water stress.(3)And in this paper,It has become a crucial research topic to explore the effects of water flooding stresses on riparian vegetation and its physiological response for the future protection of riparian plant groups.In this study,the physiological response of the antioxidant enzyme systems of the riparian plants to the water flooding stresses was explored in order to investigate its intrinsic response rules,and to provide some basic data and a theoretical basis for the protection and restoration of riparian plant communities.The dominant plant groups included Hemarthria compressa,Alternanthera philoxeroides,and Rorippa islandica.Samples were collected on the banks of the Le'an River,and these were taken as thestudy materials.An indoor soil potting culture method was used to create an artificially controlled water level in a toughened glass tank.Then,four types of different flooding stress groups were set,namely the control(CK),infiltration(INF),half flooding(HALF),and full flooding(FULL).The species growth indexes in the different stress cycles under different stress conditions and the activity changes in the antioxidant enzymes were measured,including superoxide dismutase(SOD),peroxidase(POD),and catalase(CAT).The tolerance responses of the various plant groups to the water flooding stresses were analyzed.The results showed that,under the different water flooding stresses,three different types of plants were generally able to grow normally.However,the water flooding stress inhibited the plant growth to different degrees.Furthermore,when compared with the control group,the plants' root weight,stem weight,and biomass were all significantly lower.In addition,when compared with the control group(CK),the SOD,POD,CAT and other variables of these three different plants increased to different degrees within a seven-day cycle under the different water flooding stresses.It was also observed that each species significantly increased when undergoing the full water flooding stress(FULL).The average values of the SOD,POD,and CAT of the three species were higher than those of the control group(CK),with increases of 186,310,and 263 %,respectively.During the 14-day cycle,the indexes of the SOD,POD,and CAT of the Rorippa islandica plants,as well as two types of indexes of the POD and CAT of the Alternanthera philoxeroides plants,which had undergone full water flooding stress(FULL),displayed significant decreases of 153 %,25 %,67.8 %,137 %,and 19.6 %,respectively,when compared with those which underwent the half flooding stress conditions(HALF).These results indicated that the antioxidant enzyme activities of three species were enhanced under the medium water flooding stress conditions,but weakened under the full water flooding stress conditions.