Responses Of Photosynthetic Physiological Characteristics Of Phragmites Australis And Spartina Alterniflora To Warmed Growth Temperature In Yangtze River Esthetic Wetlands

The impact of global warming on ecosystems and the response and adaptation of ecosystems to climate change have become hot spots in climate change research field in recent years.To some degree,climate warming could affect the photosynthetic physiological processes of plants,plant species interactions and ecosystem material cycle,and then lead to the change of tructure and function of ecosystem.In this study,the open-top chamber(OTC)was used to two-year simulated warming Phragmites australis and Spartina alterniflora in the Yangtze River Estuary Wetland in Chongming,Shanghai.We measured and analyzed the response of photosynthetic characteristics changes of P.australis and S.alterniflora throughout the growing season and other important physiological parameters to warming.The results will provide basic data for realizing the response of coastal wetland plant carbon assimilation to climate change,providing references for predicting invasion trend of S.alterniflora under future climate change conditions.The main conclusions as follows: 1.Except for light compensation point(LCP)and water use efficiency(WUE),the photosynthetic parameters of both plants first increased and then gradually decreased throughout the growing season under all treatment in first and second year,of which peak values of photosynthetic parameters appeared from July to September,and the variation trends were basically same as temperature and soil temperature.Compared with the control grou,two-year warming increased the photosynthetic capacity of P.australis and S.alterniflora,but the relative extent of S.alterniflora was greater.Warming enhanced significantly S.alterniflora in more months than P.australis.It indicates that S.alterniflora responds more sensitively to warming.2.The response sensitivity of different photosynthetic parameters of two plats to same warming was different.Among them,the maximum net photosynthetic rate(Pmax)and light saturation point(LSP)were the most sensitive.The mouth patterns of response of Pmax,LSP,dark respiration rate(Rd),and stomatal conductance(Gs)to warming throughout the growing season were less different between the two years,while transpiration rates(Tr),WUE,and LCP were greater.The response sensitivity of photosynthetic characteristics to warming showed obviously seasonal variation.Generally,the vigorous growth period(July-September)was the most sensitive phases,but the early and late growth periods showed lowwer sensitivity.3.Whether warming or not,the photosynthetic activity of two plants has been reduced with the proportion increase of the other side,but that of P.australis was more.It could be related to P.australis and S.alterniflora inhibited each other,and changes in canopy environment.Warming would enhance the inhibitory effect of S.alterniflora's on photosynthesis of P.australis,and causing stronger inhibition effect in the second year.Warming and planting patterns had significant interactions on Pmax of P.australis and S.alterniflora.The above showed that warming would affect the interspecific competition between P.australis and S.alterniflora by affecting the photosynthetic characteristics.4.Warming increased photosynthesis of top leaves of P.australis and S.alterniflora,but no markedly affect bottom leaves.Warming increased the photosynthetic difference between the top and bottom leaves of P.australis and S.alterniflora.It showed that the photosynthetic characteristics of top leaves responded more sensitively to warming than the bottom.5.Warming had no significant effect on stem total nitrogen content of the two plants,but significantly increased the total nitrogen content of S.alterniflora leaves(308.69%),and no significant effect on P.australis.Warming significantly increased the content of chlorophyll a,chlorophyll b and total chlorophyll in the leaves of both plants(P<0.05),but the absolute increment of S.alterniflora was greater.The contents of chlorophyll a and total chlorophyll in S.alterniflora were significantly lower than those in P.australis whether warming or not(P<0.05).Warming had no significant effect on the contents of malondialdehyde(MDA),soluble sugar and soluble protein in leaves of P.australis and S.alterniflora.The above results indicated that the changes of photosynthetic characteristics of two plants may be related to the ability of plant leaves to light utilization and some chemical changes.