Effects Of Water Level Changes In The Baisn Of Poyang Lake And Le'an River On The Physiological And Ecological Characteristics Of The Plants In The Riparian Zone In Summer

The typical wetland of Poyang Lake and Le'an River Basin is affected by its special topographic conditions and climatic conditions,there are obvious coexistence and alternation of droughts and floods in summer.Therefore,plants growing in the riparian zone are susceptible to flooding-drought stress.This research selected the dominant species of Rumex japonicus,Polygonum hydropiper and Alternanthera Philoxeroides as experimental materials to simulate water lever change pattern through the indoor potting method.Based on soil moisture moisture change pattern in the riparian zone of the Le'an River in summer,water treatment groups inclouding control?CK?,infiltration?INF?,half submerged?HS?,full submerged?FS?,control-control?CC?,control-drought?CD?,infiltration-drought?ID?,half submerged-drought?HD?,full submerged-drought?FD?were applied.We studied the physiological and ecological adaptability of three riparian plants under different soil water level,which provided a theoretical basis for the selection of phytoremediation species and population construction in riparian zones.The results were as belows.?1?After flooding for 14 days,the infiltration?INF?and half submerged?HS?treatments increased the plant stem height and biomass of the Rumex japonicus and Alternanthera Philoxeroides,but had no significant effect on the plant height and biomass of Polygonum hydropiper.By contrast,under the full submerged?FS?treatment,Rumex japonicus suffered stem breakage and leaf rot,such that the plant stem height and biomass were significantly lower?P<0.05?than those in the control group?CK?;the plant height and biomass of Alternanthera Philoxeroides were significantly higher?P<0.05?than those of CK groups?by 41.28%,38.18%,respectively?;Rumex japonicus and Alternanthera Philoxeroides increased their biomass allocation to roots and reduced the investment in stems and leaves;and the biomass allocation pattern of Polygonum hydropiper did not change significantly.In INF and HS treatment,all three species demonstrated adaptation to flooding by increasing the content of soluble sugar and soluble protein,reducing the production of membrane lipid peroxidation?MDA?,and reducing root vigor,while the soluble sugar content of Polygonum hydropiper was not significantly different from that of CK group.Under FS conditions,the content of soluble protein and soluble sugar of Alternanthera Philoxeroides and Polygonum hydropiper were significantly increased;Rumex japonicus could not adapt to the high-intensity flooding environment,leading to eventual plant mortality.The results showed that the flooding tolerance of the three herbs decreases in the order Alternanthera Philoxeroides?Polygonum hydropiper?Rumex japonicus.?2?After 14 days of drought,different indicators of different plants showed different changes.The survival rate of each treatment group was 100%,while most of the Rumex japonicus in the FD treatment group withered and died,indicating that the full submerged in the early stage inhibited its adaptability to drought stress.The values of net photosynthetic rate?P_n?,total chlorophyll content?Chlt?,effective quantum yield(Fv/Fml_ss)and root vigor of the three plant in CD groups were significantly lower than those in CC group.Conversely,the content of soluble sugar and soluble sugar and MDA in CD groups were higher than that of the CC group.With the increase of the previous flooding intensity,the ability of drought resistance in the late stage of Rumex japonicus decreased significantly and a number of plants had died in the FD group.There were no significant differences in the degree of P_n,stomatal conductance?G_s?,w?Chla?,w?Chlt?and other indicators in ID,HD and FD treatment groups of Polygonum hydropiper compared with the CD group,which indicates that the previous flooding did not increase photosynthetic physiological sensitivity to late drought stress.At the same time,the P_n,G_s,the content of soluble sugar and soluble protein of Alternanthera Philoxeroides were significantly higher than that in CC group,indicating that the full submerged in the early stage contributed to the its adaptability to the late drought stress.These changes indicated that all three plants could adapt to a certain degree of"flood-drought"stress,the adaptability of Rumex japonicus is weaker than that of Polygonum hydropiper and Alternanthera Philoxeroides?3?After the normal water supply was restored for 9ds,Alternanthera Philoxeroides and Polygonum hydropiper returned to normal growth,and some of the Rumex japonicus in FD treatment group grew new leaves.There were no significant differences in P_n,G_s,T_r,w?Chla?,w?Chlt?,Fv/Fml_ss,the content of soluble sugar and root vigor between the Polygonum hydropiper and Alternanthera Philoxeroides treatment groups compared with the CC group.It indicated that both two plants are well tolerant to flooding and drought.The values of Pn,Gs,Tr,w?Chla?,w?Chlt?,and Fv/Fml_sss in the CD,ID,and FD groups were less than or significantly smaller than in CC group of Rumex japonicus,indicating that it had a certain resilience during the rehydration stage but could not offset the damage caused by the previous water stress.The above results showed that Polygonum hydropiper and Alternanthera Philoxeroides could adapt to a certain degree of flooding and drought stress,and showed strong recovery ability in the rehydration stage,while the Rumex japonicus could not adapt to this complex water stress through growth adaptation and physiological regulation.Therefore,it is considered that Polygonum hydropiper and Alternanthera Philoxeroides could be used as alternative species for the restoration of the wetland ecosystem in the basin of Poyang Lake and Le'an River.