Relationship Between Ecological Adaptability And Geographical Distribution Of Some Dominant Caragana Species In Inner Mongolia Plateau

There are 16 Caragana species in Inner Mongolia Plateau and they are found over a vast area of land (from the east in Hulunbeier grassland, 125 E, to the west in Alashan desert, 98 E), which varies with climate and vegetation along longitudinal series. The number of species within the genus Caragana increases following the environmental gradient from the east to the west, or from forest to grassland and to then desert. In order to explore the biological basis for the geographical distribution of these Caragena species, a comparative study was conducted within and between the species in respect of growth and development, morphology structure, photosynthetic apparatus, osmotic adjustment, water metabolism, photosynthetic characteristics and protective enzymes. The results of the study are shown as follows: (1) The morphological structure and physiological characteristics of Caragana species were in adaptation to solar radiation, air temperature and humidity in their own habitats, and these were responsible for the geographical distribution of the Caraganna species. (2) The Caragana species were adaptable to their environment by means of morphological variations, water adjustment, lower transpiration, higher water use efficiency, and variations in carbon assimilation characteristics, photosynthetic apparatus and protective enzyme system. (3) The representative species of the pinnately compound leaf group - C. microphylla adapted well to the semi-arid climate, while the representative species of the pseudo-palmately compound leaf group- C. stenophylJa well adapted to semi-arid and intensively droughty climate. C, stenophylla was more adaptative to drought, high temperature and intensive radiation than C. microphylla. This provided an evidence for the viewpoint that the pinnately compound leaf group was primitive and pseudo-palmately compound leaf group was relatively advanced. (4) The adaptation strategy of the Caragana species in the desert region differed from each other: C. korshinskii, C. stenophylla and C. tibetica relied on stronger water holding ability, while C. roborovskyi relied on stronger ability of enduring water content variations. (5) C. microphylla, C. davazamcii and C. korshinskii formed a geographical cline in Inner Mongolia plateau. Taking into account the climate change of Inner Mongolia Plateau and the geographical distribution of these three species, it seeded to be reasonable to conclude that the formation of this geographical cline was the consequence of plant adaptation to natural environment. (6) In the evolutionary course of the Caragena species, there was an evident intraspecific variation within C. davazamcii, from which two morphological types were evolved, i.e., green-leaf type and gray-leaf type. (7) In sense of phylogenesis, C. davazamcii was in the position between C. korshinkii and C. microphylla. The green-leaf type C. davazamcii was similar to C. microphylla, and the gray-leaf type C. davazamcii was similar to C. korshinkii. Thus the evolutionary course could be C. microphylla- green-leaf type C. davazamcii-- gray-leaf type C. davazamcii-- C. korshinkii. (8) Genetic differentiation hadoccurred among Caragana populations in Inner Mongolia Plateau, and this indicated that the adaptation of Caragana populations to their environment was molecularly based. (9) Some certain characteristics of photosynthesis and water metabolism of Caragana species in Inner Mongolia Plateau were in relation to the water conditions of their habitats. (10) The morphological structure of leaf of Caragana species in Inner Mongolia Plateau was in accordance with their physiological and biochemical function. (11) Although the Caragana species in desert possessed many features to adapt to their environment, their adaptation was somewhat limited, and the environmental changes may have gone beyond their adaptability. In summary, the Caragana species in Inner Mongolia Plateau adapted to their environments in ways of group differentiation, species differentiation, geographical cline, morphological types and pop...