Abstract: To explore the mechanism of heat tolerance in Rhododendron hybridum under high temperature stress by foliar application of 2，4‐electrobrassinolide（EBR），inoculation with arbuscular mycorrhizal fungi（AMF）Diversifiospora epigaea，as well as their combined treatment，using Rhododendron hybridum ‘Yunqi Yanxia’cuttings as experimental materials，indoor pot experiments were conducted to investigate the effects of control（CK，normal temperature，without adding AMF or EBR treatment），separate high temperature treatment（HS），HS+AMF，HS+EBR，HS+EBR+AMF treatment on the photosynthetic pigment content，gas exchange parameters，chlorophyll fluorescence parameters，and hormone content of R.hybridum.Under high temperature stress，the growth of R.hybridum was inhibited，and the appearance phenotype was characterized by yellowing and reduced leaf size，with most leaves dying. Spraying EBR on leaves could promote the increase of AMF infection rate，branch attachment rate，and vesicles，but had no significant effect on AMF number of entry point.Compared with high temperature treatment alone（HS），the content of chlorophyll a，chlorophyll b，total chlorophyll，and carotenoids in R.hybridum increased by 84.3%，182.3%，105.8%，and 150.6%，respectively，under HS+EBR+AMF treatment.The net photosynthetic rate（Pn），transpiration rate（Tr），stomatal conductance（Gs），and instantaneous water use efficiency（WUE） increased by 129.5%，78.9%，32.7%，and 28.1%，while the intercellular CO₂ concentration（Ci） decreased by 11.7%.At the same time，HS+EBR+AMF treatment increased the maximum photochemical quantum efficiency（Fv/Fm），PSⅡ potential activity（Fv/Fo），and photochemical quenching coefficient（qP）of PSⅡ in the leaves of R.hybridum，while reducing the non photochemical quenching coefficient（NPQ）.It promoted the energy used for electron transfer per unit reaction center（E_ETo/RC），absorbed light energy per unit area（E_ABS/CSm），captured light energy（E_TRo/CSm），and quantum yield of electron transfer（E_ETo/CSm） in R. hybridum leaves.Under high temperature stress，the contents of zeaxanthin（ZT），gibberellin（GA3），and indole‐3‐acetic acid（IAA） in the leaves of R.hybridum decreased，while the content of abscisic acid（ABA）increased.After HS+EBR+AMF treatment，ZT，GA3，and IAA contents increased by 54.2%，43.2%，and 29.5%，respectively，while the content of ABA decreased by 26.5%.EBR can promote the infection and development of AMF，and compared with single AMF or EBR treatment，the combination of the two treatments has the best effect on enhancing the heat tolerance of R.hybridum.

Key words: Rhododendron hybridum；High temperature；2, 4‐epibrassinolide；Arbuscular mycorrhizal fungi；Chlorophyll；Hormone metabolism；Photosynthesis

摘要： 为探究高温胁迫下叶际施用2，4-表油菜素内酯（EBR）、接种丛枝菌根真菌（AMF）地表多样孢囊霉（Diversispora epigaea）及其复合处理对四季杜鹃耐热性的影响机制，以四季杜鹃（Rhododendron hybridum）云栖烟霞扦插苗为试验材料，采用室内盆栽试验，研究对照（CK，正常温度，不添加AMF、EBR）、单独高温（HS）、HS+AMF、HS+EBR、HS+EBR+AMF处理对四季杜鹃光合色素含量、气体交换参数、叶绿素荧光参数以及激素含量的影响。结果表明，高温胁迫抑制四季杜鹃生长，外观表型上表现为叶片黄化变小，大部分叶片枯死。叶片喷施EBR可以促进AMF侵染率、丛枝着生率以及泡囊数的增加，但对侵入位点数无显著影响。与HS处理相比，HS+EBR+AMF处理下四季杜鹃叶绿素a、叶绿素b、总叶绿素和类胡萝卜素含量分别增加84.3%、182.3%、105.8%和150.6%，净光合速率（Pn）、蒸腾速率（Tr）、气孔导度（Gs）和瞬时水分利用效率（WUE）提高129.5%、78.9%、32.7%和28.1%，胞间CO₂浓度（Ci）下降11.7%；同时，HS+EBR+AMF处理增加了四季杜鹃叶片中PSⅡ最大光化学量子效率（Fv/Fm）、PSⅡ潜在活性（Fv/Fo）以及光化学猝灭系数（qP），降低了非光化学猝灭系数（NPQ），对四季杜鹃叶片中单位反应中心用于电子传递的能量（E_ETo/RC）、单位面积吸收的光能（E_ABS/CSm）、捕获的光能（E_TRo/CSm）、电子传递的量子产额（E_ETo/CSm）具有促进作用。高温胁迫下，四季杜鹃叶片中玉米素（ZT）、赤霉素（GA₃）、生长素（IAA）含量降低，而脱落酸（ABA）含量增加，HS+EBR+AMF处理后ZT、GA₃、IAA含量分别增加54.2%、43.2%和29.5%，ABA含量下降26.5%。综上，EBR可以促进AMF对植物的侵染，相较于单一AMF或者EBR处理，二者复合处理下增强四季杜鹃耐热性的效果最好。

关键词: 四季杜鹃；高温；2, 4-表油菜素内酯；丛枝菌根真菌；叶绿素；激素代谢；光合作用