Analysis of changes in anatomical characteristics and physiologic features of heteromorphic leaves in a desert tree, Populus euphratica

摘要

Populus euphratica Oliv. is well-adapted to extreme desert environments and possess the characteristic of heterophylly. On the same tree, the lanceolate, broad-ovate, and dentate broad-ovate leaves distribute in the different tiers of the canopy. The lanceolate leaves distribute on the lower canopy, broad-ovate leaves on the middle canopy, and dentate broad-ovate leaves on the upper canopy. The leaf structure was found to be xeromorphic. The stomatal densities of the three typical leaves were different and decreased in value from dentate broadovate, to broad-ovate, and to lanceolate leaves. The osmotic potentials at full and zero turgor were lowest in dentate broad-ovate leaves. In an appropriate growth environment, the chlorophyll fluorescence parameters of the three leaf types were almost the same and significantly changed upon exposure to short-term water stress. These results showed that dentate broad-ovate leaves can maintain their normal size and shape under arid and hot conditions because of their relatively thick cell wall and high mechanical strength. Moreover, dentate broad-ovate leaves had more developed vascular bundles in the main vein than the other types and thus more efficiently transported water and salts. These results suggested that dentate broad-ovate leaves can efficiently adapt to changing conditions, with more obvious xeromorphic characteristics and a relatively higher photosynthesis rate under drought conditions, compared with the others leaf types.