Study On The Optimization Selection Of Rhododendroncultivarsin West Lake Scenic Spot In Hangzhou

Rhododendron is one of the ten traditional flowers in China,which is called the "flower of beauty".As an excellent garden flowering shrubs,it plays an important role in the Color Upgrade Project of Hangzhou West Lake scenic spot.However,in the application of actual landscaping,the problems such as high temperature,lack of soil water supply and other factors or because of the high canopy density,resulting in poor growth of Rhododendron,showing sparse plants,less flowers,flowering delay and so on.Therefore,this paper first selects 13 cultivars of Rhododendron which are in the application of the West Lake scenic spot and have high ornamental value as the test material,including（Da Qinglian,Hong Shanhu,Fen Shanhu,Da Yuanyangjin,Yan Zhimi,Hong Yue,Lan Ying,Xin Tiandi,Liu Qiuhong,Zhuang Yuanhong,Guo Qihong,Yu Hudie,Zi E）.Through the method of screening and rescreening as well as the continuous drought and artificial potted controlling water,the leaf wilting degree was identified and the index of relative water content,water saturation deficit,relative conductivity,Fv/Fm,Fv/Fo,MDA,CAT,soluble protein,soluble sugar content were measured,finishing the study on screening of drought resistance of 13 Rhododendron cultivars.Besides,the rhododendron wasmade shading treatment by erecting artificially different shading rate（0,55%,75%,90%）of the sun shading net,synthetically determining and analyzing the shape index（leaf length,leaf width,leaf thickness,crown width,plant height）,physiological indexes（chlorophyll content,leaf mass,leaf water content）and photosynthetic indexes（light compensation point,light saturation point,the maximum net photosynthetic rate,respiration rate,apparent quantum efficiency）etc,finishing the study on screening of shade tolerance of 13 Rhododendron cultivars.The paper provides scientific basis for the cultivation management and landscape application of Rhododendron.The conclusions of this study are as follows:（1）The drought resistance screening test result shows that the wilt level and relative conductivity of all the cultivars have increased with the time of drought stress increased;relativewater content has decreased with the stress level increased;Fv/Fm and Fv/Fo decreased significantly under severe stress.Comprehensive evaluation of membership functions suggests that the cultivars of Guo Qihong,Yu Hudie,Yan Zhimi and Da Qinglian have better drought resistance than the other 9 cultivars of Rhododendron.To study the mechanism of drought resistance of Rhododendron further,the 4 cultivars acquired in the early screening test were carried on deeper researchand the rescreening tests show that:with drought stress degree deepened,the relative water content and water saturation deficit declinedsignificantly（P<0.05）,and it is positively related to drought stress level;MDA and relative conductivity rate value are raised with drought stress degree deepened;Fv/Fm reduce significantly in heavy degrees stress condition;soluble protein and soluble sugar content show different results due to the different cultivars;the CAT activity of other cultivars decrease under severe stress except the Yu Hudie.（2）The shading tolerance screening test result shows that the chlorophyll a,chlorophyll b,total chlorophyll,leaf area ratio and relative water content have increased with stress degree deepened and the differences between each index are significant（P<0.05）.Comprehensiveevaluation of membership funcationsresult suggests that Zi E,Zhuang Yuanhong,Yan Zhimi and Liu Qiuhong have better shading tolerance than the other 9 Rhododendroncultivars.To study the mechanism of shading tolerance of Rhododendron further,the 4 cultivars acquired in the early screening test were carried on deeper research by measuring 17 indexes and the rescreening test shows that: with the shading degree increased,the plant morphological characteristics such as leaf length,leaf width,crown width,plant height have increased,but the leaf thickness has decreased;the dry weight,fresh weight and the water content of per unit area decreased gradually with the stress level deepened;chlorophyll a,chlorophyll b,total chlorophyll content increased with the increase of stress gradient increased,while chlorophyll a/b decreased;the light saturation point of 4 cultivars are in the range of 800¹200μmol·m^-2·s^-2,light compensation are 10²5μmol·m^-2·s^-2 and dark respiration rate are 0.3⁰.9μmol·m^-2·s^-2.The three are decreased with the increasing degree of shading and the apparent quantum efficiency is not significantly decreased.（3）The comprehensive drought resistance screening and rescreening tests show thatthe drought resistance of 13 cultivars of Rhododendron is as follows: Guo Qihong>Yu Hudie>Da Qinglian>Yan Zhimi>Da Yuanyangjin>Lan Ying>Zhuang Yuanhong>Hong Yue>Xin Tiandi>Zi E>Liu Qiuhong>Fen Shanhu>Hong Shanhu.Correlation matrix analysis and principal component analysis show that the 5 indexes of CAT,MDA,soluble sugar,relative electricalconductivity and relative water content have significant effects on drought resistance.（4）The comprehensive shading tolerance screening and rescreening tests show that the shading tolerance of 13 cultivars of Rhododendron is as follows: Zhuang Yuanhong（Zi E）> Yan Zhimi > Da Yuanyangjin > Liu Qiuhong > Da Qinglian > Hong Yue > Lan Ying > Hong Shanhu > Fen Shanhu > Guo Qihong > Xin Tiandi > Yu Hudie.Correlation matrix analysis and principal component analysis show that the 5 indexes of leaf thickness,chlorophyll a,total chlorophyll content,specific leaf mass and per unit area water content have significant effects on shading tolerance,and the Rhododendron grow best under shade in 55% rate.