胡杨异形叶叶绿素荧光特性对高温的响应

Response of chlorophyll fluorescence characteristics of Populus euphratica heteromorphic Leaves to high temperature

胡杨(Populus euphratica Oliv)是塔里木极端干旱荒漠区优势乔木树种,由于其生长在荒漠环境中,极端高温远高于其它地区,因此研究胡杨对高温胁迫的响应特征对于解释胡杨的抗逆机理与生态适应策略具有极为重要的意义。以胡杨3种典型的异形叶为材料,研究不同温度对其叶绿素荧光特性和能量分配的影响。结果表明,25—45℃温度下胡杨异形叶的F0、Fm、Fv/Fm与Fv/F0变化不大,尤其Fv/Fm仍能保持在0.78左右,光合反应正常;高温胁迫下(>45℃)Fm、Fv/F0、Fv/Fm、F′v/F′m、qP、ΦPSⅡ、P和ETR均大幅降低;F0、qN、E显著上升,而D先上升后下降,说明高温抑制了PSⅡ的功能,使PSⅡ反应中心活性下降,QA-的还原速率加快,光化学电子传递速率降低,某些能量耗散途径受阻,影响了PSⅠ和PSⅡ激发能的平衡分配,最终导致光合机构受损、光合速率降低。胡杨3种异形叶的叶绿素荧光参数随温度升高变幅不同,高温处理下锯齿阔卵形叶各参数均高于卵形叶与条形叶,表明锯齿阔卵形叶比卵形叶和条形叶具有更强的高温耐受能力。用模糊数学的隶属度函数对胡杨3种异形叶的耐热性进行综合评价,锯齿阔卵形叶的耐热性最强。

Populus euphratica Oliv,a member in the family Salicaceae,is typical xeromorphic mesophyte and an important tree species of desert riparian forests in arid regions.It is mainly distributed in central Asia,west Asia and the Mediterranean region,especially in the basins of inland rivers of the northwest arid regions of China where it occupies the widest distribution area.The largest and most typical desert riparian forest is found along the Tarim River and occupies over 350,000 km2.P.euphratica possesses many excellent characteristics such as tolerance to cold,high temperature,drought,salt and alkali soils.It plays an active role in climatic regulation,desert extension management,river bank protection,channels stabilization and oasis conservation.It has not only protected desert fragile ecological system but also been an irreplaceable natural barrier.P.euphratica is highly prized in the Tarim Basin for its great ecological,economical and social benefits.During the growth and development of P.euphratica,the leaf morphology changes in order to adapt drought,high temperature stress in extremely arid desert region of Tarim basin.In most cases,a single adult tree commonly comprises polymorphic leaves,including lanceolate,oval and serrated broad-oval leaves.The lanceolate,oval and serrated broad-oval leaves come out in turn.In one plant with multiple types of leaf shapes at the same time,the heteromorphic leaf distribution in the canopy from top to bottom is serrated broad-oval,oval and lanceolate,respectively.In this study some standard adult plants with three typical leaf shapes were selected from the planted forest stands in Tarim basin.The purpose of the study was to measure physiological responses of P.euphratica to high temperature stress and to understand drought-resistance mechanism of this tree species under heat stress conditions..Seven temperature treatments with 25℃,30℃,35℃,40℃,45℃,50℃ and 55℃ were designed to compare the responses of three heteromorphic leaves of P.euphratica including chlorophyll fluorescence characteristics and excitation energy distribution in growth chamber.The results showed that there were slight variations in F0,Fm,Fv/Fm and Fv/F0 of P.euphratica heteromorphic leaves from 25℃ to 45℃.The ratio of Fv/Fm was observed to maintain 78% of normal photosynthesis reaction.Yet,a few parameters such as Fm,Fv/F0,Fv/Fm,Fv/F′m,qP,ΦPSⅡ,P and ETR were significantly decreased with heat stress（45℃）,and the values of F0,qN and E were found to increase significantly.The level of D parameter increased at the initial stage and decreased at the later stage.The results indicate that high temperature stress decreased the activity of PSⅡreaction center and photochemical electron transfer rate,inhibited the heat dissipation and distribution balance of excitation energy between PSⅠand PSⅡ,which led to the structural damage of photosynthetic apparatus and functional descend in photosynthetic ability.The chlorophyll fluorescence parameters of P.euphratica heteromorphic leaves varied significantly from each other in seven temperature treatments.Furthermore,the chlorophyll fluorescence level of serrated broad-oval leaf was significantly higher than that of lanceolate and oval leaf.This demonstrated that serrated broad-oval leaf had better tolerance to heat stress than other leaf types did.Finally,the membership function of fuzzy mathematics was used to analyze the tolerance abilities of three heteromorphic leaves under heat stress.The results indicates that the serrated broad-oval leaf was the most tolerant to heat stress.