内蒙古高原荒漠区几种锦鸡儿属(Caragana)优势植物的生理生态适应特性

比较了内蒙古高原荒漠区4种锦鸡儿属(Caragana)优势植物——柠条锦鸡儿、狭叶锦鸡儿、垫状锦鸡儿和荒漠锦鸡儿的生理适应特性。研究发现:4种锦鸡儿属植物中,荒漠锦鸡儿的叶片含水量、束缚水/自由水比值、水势以及水分利用效率最低,气孔导度日变化表现为与气温变化相似的早晚低、中午高的单峰曲线。4种锦鸡儿蒸腾速率日变化状况相似,均在10:00达到最大,以后逐渐降低,但日蒸腾积累值垫状锦鸡儿<荒漠锦鸡儿<柠条锦鸡儿<狭叶锦鸡儿。相比较,柠条锦鸡儿、狭叶锦鸡儿和垫状锦鸡儿对当地的水分条件有良好的适应性,能够保持较好的水分状况,水分亏缺在15%以下,而荒漠锦鸡儿叶水分亏缺日变幅较大,保水能力不及其它3种。渗透调节比较研究发现:荒漠锦鸡儿的渗透势最低,细胞质离子浓度最高,无机渗透调节物产生的渗透势所占的比例也更大,说明其低渗透势的维持主要来自无机渗透调节物质的较多积累。保护酶和自由基比较研究发现:POD和SOD活性荒漠锦鸡儿明显高于其它3个种,但CAT活性在4种植物中无显著差别;叶片自由基含量狭叶锦鸡儿>荒漠锦鸡儿>柠条锦鸡儿>垫状锦鸡儿。这些结果表明:(1)荒漠锦鸡儿对干旱环境的适应方式与其它3种不同,柠条锦鸡儿、狭叶锦鸡儿和垫状锦鸡儿以强保水能力、维持稳定的水分而适应,而荒漠锦鸡儿以更负的渗透势、更高细胞质离子浓度弥补其更多的水分消耗和对水分变化的强耐性而适应,较高的保护酶活性可能是其强耐性的生理基础之一。(2)保水能力弱的锦鸡儿种主要通过无机离子的积累,调节细胞质渗透势,保持水分平衡,这是一种相对节省能量的适应对策。

A Comparison of ecophysiological characteristics of four dominant Caragana species in adaptation to Desert Habitat of the Inner Mongolia Plateau

Caragana species grow mainly in the arid and semi-arid areas of Asia and Europe.Geographically,the number of species declines with increasing precipitation and temperature,and increases with increasing altitude.They typically grow in grasslands or deserts,but are sometimes found in forests.The adaptation of these Caragana species to the climatic conditions of the desert has made them become dominant plants in the desert.In desert regions there are high temperatures,strong solar radiation and very little precipitation.Among these environmental factors,the growth and development of plants are most influenced by precipitation.What made these species become adaptive to the climate of a desert region? To answer this,the eaophysiological characteristics of four dominant Caragana species-Caragana korshinskii,C.stenophylla,C.tibetica and C.roborovskyi,which grow in the desert area of the Inner Mongolia Plateau,were investigated.Leaf water content,the ratio of bound water to free water,leaf water potential and water-use efficiency of C.roborovsky were lowest among four Caragana species.The diurnal change of stomatal conductance of C.roborovskyi was different from that of the other species,and corresponded to the changes of daytime temperatures which were low on morning and afternoon,high during noon,and presented a single peak curve.Diurnal changes of transpiration rate of four dominant Caragana species were similar,and they all reached their maximum at 10:00 am,and then decreased gradually.The order for the daily cumulative value of transpiration was as follows:C.tibetica < C.roborovsky < C.korshinskii < C.stenophylla.Based on adaptations to water conditions of arid environment,C.korshinskii,C.stenophylla and C.tibetica to maintained good water status-leaf water deficit was lower than 15%.While the C.roborovsky's diurnal change range of leaf water deficit was much wider,its ability of keeping water was not as great as that of the other three Caragana species.Result from studies on the osmotic adjustment indicated that C.roborovsky had the lowest osmotic potential and highest leaf cytoplasm ion concentration.The lower the osmotic potential in the Caragana species,the more contribution of inorganic ions were to the total negative osmotic potential,which hinted these negative osmotic potential came from accumulation of inorganic ions.Results from studies on antioxidative enzyme systems and free radical content showed that activities of POD and SOD were highest in C.roborovskyi among the four species,while the activity of CAT kept similar between the four species.The order of free radical content was as follows:C.stenophylla > C.roborovskyi > C.korshinskii > C.tibetica.From these eaophysiological characters,we arrived at two main conclusions,as follows:(1) Adaptation strategy of C.roborovsky to drought was different from that of the other three species.C.korshinskii,C.tibetica and C.stenophylla were adaptable to arid environment through a greater ability of preserving water to keep water status stable,while C.roborovsky might rely on its lower osmotic potential and higher leaf cytoplasm ion concentration to supplement excess water consumption.C.roborovsky rely on greater ability of enduring variations in water conditions to adapt to its arid habitat too,and its fairly high activities of antioxidative enzymes might be one of the physiological bases for its stronger ability of endurance.(2) The low water retaining ability of Caragana species adjusted their cytoplasm osmotic potential mainly through accumulating inorganic ions,and thereby maintained water balance.This is probably an energy-saving adaptation strategy.