Study On The Heat Tolerance Of Sorbus In The High Plain And Low Mountain Areas Of Beijing

Sorbus is one of the important Chinese native tree species with high ornamental value ranging from 500 t o 2 000 m altitude.In order to gradually realize the introduction and application of Sorbus in Beijing and other North China plain areas,it is necessary to gather and screen excellent germplasm resources of So rbus,and gradually introduce it from the middle or high altitude mountainous areas to the low altitude a reas,such as Beijing and other cities in the North China plain.The greater the difference of altitude gra dient,the more difficult the introduction and cultivation of sorbus.The main factor limiting the successfu l introduction of Sorbus to Beijing is the high temperature in summer.In the hot summer in the low alt itude plain area,the seedlings of Sorbus will seriously burn,and even the whole plant will die.Therefor e,it is a very meaningful study to establish a complete evaluation system of Sorbus clones by comparin g the natural high temperature heat resistance of different clones.In this study,we screened out good he at-resistant clones of Sorbus in the field,and explored the influence of altitude gradient and seedling age on the summer over ability of Sorbus,and provided reliable basis for the introduction and landscape ap plication of Sorbus.(1)In this study,the field trial for heat resistance of different clones was evaluated comprehensively,which provides scientific basis for fine varieties early selection adapted to Beijing high plains.2-year-old grafted seedlings of 14 clones from 5 provenances were used as materials.In the field trial,which performed in Yanqing County of Beijing with 500 m altitude,the height and stem growth of seedlings,content of malondialdehyde(MDA),soluble protein,soluble sugar,chlorophyll in the leaves,activity of superoxide dismutase(SOD)and peroxidase(POD)in the leaves were measured;And the heat resistance of 14 clones was evaluated comprehensively by membership function analysis based on principal component analysis.The value of each single index showed significant difference among 4 months and was significantly different among different clones.The growth performance of Wuling1(WL1)?Wuling2(WL2)?Shihui1(SH1)and Shihui2(SH2)was significantly better.The growth performance of Taibai1(TB1)and Taibai2(TB2)was the worst;The MDA content of TB1 and TB2 increased most significantly from May to June,showing poor heat resistance.However,the MDA content of Fengning2(FN2)and WL2 decreased,showing stronger heat resistance than other clones;The activity of two protective enzymes of WL2,Fengning1(FN1)and FN2 was higher than that of other clones.The chlorophyll content of FN1 and FN2 was minimally impacted by high temperature;The content of osmotic regulator of Songshan1(SS1)?Songshan2(SS2)?Songshan3(SS3)and Songshan4(SS4)was higher than that of other clones;Correlation analysis showed significant positive correlation exists between every two groups of chlorophyll content(P<0.01);Chlorophyll and ground diameter growth(P<0.05)was significantly negatively correlated;Significant positive correlation was found between height and ground diameter of seedlings;After principal component analysis,10 single indexes were transformed into 4 new independent comprehensive indexes;After the comprehensive evaluation of the membership function,the sequence of field heat resistance of each clone seedling from strong to weak is: WL2,WL1,FN1,SH2,SH1,FN2,SS2,Huangshan shuiyu2(HS2),SS4,SS3,SS1,Huangshan shuiyu1(HS1),TB2,TB1.(2)In order to explore the difference of summer overing ability of Sorbus pohuashanensis at different altitude gradients,this paper analyzed the changes of MDA content,SOD and POD enzyme activity,soluble sugar content and other physiological indexes of Sorbus pohuashanensis at 200 m,300m and 460 m altitude in Xishan Forest Farm of Beijing.The order of the stability of active oxygen metabolism of Sorbus pohuashanensis was x-460,x-300 and X-200.The stability of active oxygen metabolism in summer was affected by altitude gradient,and increased with altitude gradient.The order of photosynthetic capacity in different altitude gradients was x-460,x-300 and X-200.The photosynthetic capacity of Sorbus pohuashanensis was affected by the altitude gradient,and increased with the rise of elevation gradient.The permeabilities of different altitude gradients were x-300,x-460 and X-200.There is no certain rule between the altitude gradient and the osmoregulation ability of Sorbus pohuashanensis mandshurica in summer.