Morphological adaptation of four dominant Caragana species in the desert area of the Inner Mongolia Plateau

MA Cheng-Cang~(1,2),GAO Yu-Bao~(1,*),GUO Hong-Yu,WU Jian-Bo~1,WANG Jin-Long~1 (1.College of Life Science,Nankai University,Tianjin 300071,China;2.Department of Biology,Tianjin Normal University,Tianjin 300074,China).  

Caragana species grow mainly in the arid and semi-arid areas of Asia and Europe.Geographically,the number of Caragana species declines with increasing precipitation and temperature,as well as increases with rising altitude.They may be found in forest,grassland and desert ecosystems,but more often in grassland and desert.The adaptation of these Caragana species to the climatic conditions of the desert has made them become dominant plants in the desert.In desert region there is very little precipitation,high temperature and strong solar radiation.Among these environmental factors,precipitation affects most the growth and development of the plants there.What made these species be adaptive to the climate of a desert region? To answer this,the distribution and morphological adaptation of four dominant Caragana species —C.korshinskii,C.stenophylla,C.tibetica and C.roborovskyi in the desert area of the Inner Mongolia Plateau were studied.An analysis on geographical distribution,growth and developmental pattern indicated that these four Caragana species grew normally in the Alashan region,and were adapted to the desert environment there.The leaf of C.stenophylla took the form of tile(tegular),which hindered gas exchange to a certain extent and reduced the area receiving solar radiation.The leaf of C.tibetica was tube-shaped,which resulted in a potentially greater obstruction for gas exchange and a smaller area receiving solar light.The C.korshinskii with densely fallen silky villis,C.stenophylla with densely offwhite villis,C.tibetica with densely silky villis,and C.roborovoskyi with densely straight silky villis had strong reflecting ability,which could lower their leaf temperature,and therefore reduce their transpiration rate.The strip-shaped leaf in C.stenophylla and C.tibetica,and small leaf area,great ratio of thickness to area,less leaf biomass,and specific leaf area(SLA) in four desert Caragana species led to the reduction in area of transpiration and radiation reception,thus enhancing these four desert Caragana species' ability to preserve water.All these features enable these desert Caragana species to adapt to the arid environment where atmospheric temperature is high and solar radiation is intensive.These desert Caragana species had low chlorophyll content.Such low chlorophyll content and offwhite villis or silky villis resulted in a paleness of leaf color,which enabled the four Caragana species to avoid strong solar radiation.For this reason,the plants had lower leaf temperature and their transpiration was decreased so that they were able to adapt to their habitats well.This was a characteristic in adaptation to intensive sunlight,high temperature and long-lasting drought.Higher Chl.a/b in C.korshinskii and C.tibetica was an adaptation to intensive sunlight.By comparing the morphological characteristics of these four species,we found that the patterns of adaptation to the arid environment were different from each other in the four desert Caragana species.

【Key Words】： Caragana desert adaptation morphology chlorophyll content
【Fund】： 国家重点基础研究发展规划资助项目(G2000018601)~~
【CateGory Index】： S793;Q944.3

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