Effects Of High Temperature Stress On The Growth And Physiology Of Three Rhododendron Species

Rhododendron species are rich and diverse,and different rhododendron varieties have varying resistance and adaptability to high temperatures.In recent years,due to frequent human activities,the production of greenhouse gases has intensified,leading to global warming.Especially in recent years,the summer temperature in Changsha has repeatedly reached new highs,and the duration of high temperatures has been continuously extended,leading to a continuous increase in the mortality rate of rhododendrons in Hunan Province.To address the series of issues related to the adaptability of Rhododendron to high-temperature environments,Rhododendron rivulare Hand.-Mazz.,R.latoucheae Franch,and R.more(Blum)G.were selected Don)was used as the experimental material and an artificial climate box was used to maintain air humidity as a constant value,and four different temperature environments were created:control 25℃(day)/21℃(night),mild stress 32℃(day)/25℃(night),moderate stress 38℃(day)/28℃(night),and severe stress 42 ℃(day)/31℃(night).Study the effects of high temperature stress on the growth and physiological indicators of three species of rhododendrons,providing a theoretical basis for their resistance to high temperature.The main research findings are as follows:(1)As the degree of high temperature stress increases,its impact on the growth of three species of rhododendrons gradually increases.As the degree of high temperature stress increases,the growth indicators of the three rhododendrons,including plant height increment,ground diameter increment,relative water content of leaves,and total biomass,all show a significant decrease.Compared with the control(excluding total biomass),the order of decrease in plant height increment,ground diameter increment,and relative water content of leaves for the three rhododendrons is:R.rivulare Hand.Mazz.>R.more(Blum)G>R.latoucheae Franch,The order of decrease in total biomass is as follows:Rhododendron by the R.rivulare Hand.-Mazz.>R.latoucheae Franch>R.more(Blum)G;With the strengthening of high temperature stress,the root to shoot ratio of the three rhododendrons showed a trend of first increasing and then decreasing,and the overall trend showed an upward trend.Compared with the control group,the order of increase in the root to shoot ratio of the three rhododendrons was as follows:R.more(Blum)G>R.rivulare Hand.-Mazz.>R.latoucheae Franch.(2)As the degree of high temperature stress increases,its impact on the anatomical structure of the leaves of three species of rhododendron gradually increases.As the degree of high temperature stress increases,the leaf thickness,upper epidermis thickness,lower epidermis thickness,and sponge tissue thickness of the three rhododendrons show a continuous decreasing trend.Compared with the control,the order of the decrease in the above indicators is:R.rivulare Hand.-Mazz.>R.more(Blum)G>R.latoucheae Franch.At the same time,as the degree of high temperature stress increases,The thickness of Palisade cell and the ratio of the thickness of Palisade cell to the thickness of sponge tissue in the leaves of the three Rhododendron species showed a gradually increasing trend.Compared with the control,the order of increase was:R.rivulare Hand.-Mazz.>R.more(Blum)G>R.latoucheae Franch.(3)As the degree of high temperature stress increases,its impact on the photosynthesis of the three rhododendrons gradually increases.As the degree of high temperature stress increases,the chlorophyll a,chlorophyll b,carotenoid content,and total chlorophyll content in the leaves of the three rhododendrons show a gradually decreasing trend.With the increase of high temperature stress time,the chlorophyll a,chlorophyll b,carotenoid content,and total chlorophyll content in the leaves of the three rhododendrons show a gradually decreasing trend,The descending order of the above indicators for the three types of rhododendrons is:R.more(Blum)G>R.rivulare Hand.-Mazz.>R.latoucheae Franch.With the strengthening of high temperature stress,the gas exchange parameters Pn,Gs and Tr of the leaves of the three species of rhododendron showed a continuous downward trend.Compared with the control,the descending order of the above indicators of the three species of rhododendron was:R.rivulare Hand.-Mazz.>R.more(Blum)G>R.latoucheae Franch.At the same time,with the increase of high temperature stress,the Ci of the leaves of the three species of rhododendron showed a gradually increasing trend,compared with the control,The order of elevation is:R.rivulare Hand.-Mazz.>R.more(Blum)G>R.latoucheae Franch.(4)As the degree of high temperature stress increases,its impact on the physiology of the three rhododendrons gradually increases.As the degree of high temperature stress intensifies,the SOD content in the leaves of the three rhododendrons shows a gradually increasing or first increasing and then decreasing trend.Among them,the SOD content of the staghorn rhododendron shows a gradually increasing trend,while the other two rhododendrons show a trend of first increasing and then decreasing.Compared with the control,the overall trend shows an increasing trend.The order of the increase in SOD content of the three rhododendrons is:R.rivulare Hand.-Mazz.>R.more(Blum)G>R.latoucheae Franch;With the increase of high temperature stress time,the SOD content in the leaves of the three rhododendrons showed a trend of first increasing and then decreasing.As the degree of high temperature stress increases and the duration of stress increases,the MDA content in the leaves of the three rhododendrons shows a gradually increasing trend.Compared with the control,the order of MDA content increase in the three rhododendrons is:R.rivulare Hand.-Mazz.>R.more(Blum)G>R.latoucheae Franch.As the degree and duration of stress increased,the soluble protein and soluble sugar content of the three rhododendrons showed a gradually increasing or first increasing and then decreasing trend.Compared with the control,the overall trend was increasing.The order of increase in soluble protein and soluble sugar content of the three rhododendrons was:R.latoucheae Franch>R.more(Blum)G>R.rivulare Hand.-Mazz..The membership function method was used to analyze the changes in various growth and physiological indicators of three types of rhododendrons before and after high temperature stress,and the corresponding membership function values were calculated.The order of heat resistance of the three types of rhododendrons studied was:R.latoucheae Franch>R.more(Blum)G>R.rivulare Hand.-Mazz..