两种土壤条件下山杨幼苗不同叶位叶片适应干旱胁迫的光合特性分析

The effects of soil type on photosynthetic characteristics of different leaf-position of potted Populus⁃Tremuloides under drought stress

[目的]本文通过研究叶片对不同土壤类型下的干旱胁迫的响应特征,揭示杨树不同叶位叶片光合作用对干旱胁迫的适应策略及耐旱机制,为不同土壤类型的旱区造林提供科学依据。[方法]以3~4月龄的山杨(Populustremuloides)幼苗作为材料,加拿大常用的商业混合土(PMX)和典型的山杨生长的土壤(ELL)为供试土壤,采取土壤逐渐干旱的方法进行控水试验,对山杨幼苗的叶片伸长生长,植株上、中、下部叶片的光合特性等参数进行测定,比较干旱胁迫下两种土壤类型对山杨幼苗生长及光合特性的影响。[结果]干旱胁迫下,较为紧实的土壤(ELL)中,土壤含水量较高,但可利用水分较低;杨树幼苗在干旱处理前期加速生长,尽可能多的获取资源来积累生物量,但存活的时间较短;此外,ELL基质上的幼苗会把有限的水资源优先供应给生长比较旺盛的上部叶片,加速生长,并保持较高的光合活性;较为疏松的土壤(PMX)保水性差,失水快,但土壤有效水分较高,杨树幼叶受旱后采取保守策略,叶片减缓生长,植株存活时间较长,具有较高的耐旱性。此外,干旱处理前期土壤中有限的水分优先供应功能比较成熟的中部叶片,中部叶片的光合活性、WUE也较高,直至干旱后期才转移至上部叶片。干旱中前期(≤8 d)光合速率的下降主要是气孔限制因素,后期主要是非气孔限制因素引起,而PMX基质上幼苗叶片的光合能力则可能还受其它因素如叶肉细胞导度(gm)等影响。

[Object]By studying the response characteristics of leaves to drought stress under different soil types,this paper re⁃veals the adaptation strategies and drought tolerance mechanisms of leaf photosynthesis in different leaf positions of poplar trees to drought stress.This research provided a scientific basis for afforestation in arid areas of different soil types.[Method]In a progressive drought condition,3-4 month-old P.tremuloides seedlings were used as materials to test the difference in leaf growth and photosynthetic characters between two soil types,PMX(potting mix)and ELL(Typical soil for poplar,collected from Ellerslie Research Station),by measuring leaf growth and gas exchange.The results showed that under drought stress,in the more compact soil(ELL),the soil moisture was higher but the effective moisture was lower.The young poplar seed⁃lings grew faster in the early stage of drought treatment to accumulate the resources and biomass,but their survival time was short.In addition,the seedlings in the ELL substrate gave priority to limited water resources to the upper leaves,which had more vigorous growth and maintained high photosynthetic activity.On the other hand,the relatively loose soil(PMX)had poor water retention and lost water faster,but the soil’s effective moisture was higher.Under drought stress,the young plants took a conservative strategy,and the leaves slowed down their growth.The plants survived longer had higher drought resis⁃tance.In addition,in the early stage of drought treatment,the preferential water supply was to the more mature leaves than the middle leaves,and the photosynthetic activity and water use efficiency(WUE)in the middle leaves were higher.As the drought progressed,the water supply was transferred to the upper leaves.The main limiting factor for the decrease in photosyn⁃thetic rate in the early stage of drought(less than 8 d)was stomatal conductance,and later it was mainly caused by non-stoma⁃tal restriction.The photosynthetic capacity of the leaves on the PMX substrate may be influenced by other factors such as meso⁃phyll cell conductivity(gm).