Characteristics Of Phenology And Physiological Ecology Of Populus Euphratica Oliv. In Ejina

Populus euphratica (Populus euphratica Oliv.) is the only tree species in dry desert in Ejna Banner that can replace and form forests naturally, which is very important in ecological and economical construction in the area. In order to fully understanding the living and growing feature of the Populus euphratica, we have studied P. euphratica from phenology and physiological ecology in Ejina Banner. The results were showed:1. Underground the adverse growing environment in this area, the height growth of P. euphratica has been inhibited obviously. So we depend on the leaf shape and distribution characteristics, DBH and if stoutly,but not the height of the P. euphratica, as the primary index, the age levels of the matural P. euphratica tree can be divided as:Four age levels of seedling, young tree, mature tree and overmature tree. Based on the main composition of the forest, the different forest stand have been divided3ages of young, mature and overmature growth.2.According to the study of the forest stand, we understood that the main growing strategies is that to distribute the resource to sprout tillers for regeneration, and to give up the rejuvenation of the canopy.3. By two-way indicator species analysis (TWINSPAN) and the distended canonical correspondence analysis (DCCA), we know that the level of underground water is the main environment factor of all for the distribution of the phytocoenosis which underground of the P. euphratica trees. The river is main effect factor for the vegetative cover in the P. euphratica trees which growing on the river bank.4. P. euphratica tree is a kind of heterophyll trees, according to the proportion of length and wide of the leaves, can be divided into broad leaves and narrow leaves. The time for sprouting, expansion, discolour and defoliation of broad leaf is about5～10days earlier than narrow leaf., only the defoliation cycle is longer. The leaves expansion method is different, for the narrow leaf be expansion in order, the two peak expansion times will appear in April and June; and the broad leaf the peak expansion time only appears in April. The amount of leaves on single branch of narrow leaf is more than the amount of leaves on broad leaf. The construction cost for the single leaf of the broad leaf is more than narrow leaf.5. The optical compensation point and saturation point of the narrow leaf of P. euphratica are lower than those of broad leaf for14.5%and42.9%respectively, and when at the optical saturation pint, the maximum net photosynthesis speed is lower than that of the broad leaf for69.5%. The transpiration rate of narrow leaf is higher than broad leaf and yang tree same as..6. The main moisture losing method for either narrow or broad leaf of P. euphratica is stomatal transpiration.Ψπ0of mature tree and immature broad leaf of P. euphratica are lower than those of narrow leaf for about26.1%and11.9%respectively, and Va%s are higher than those of narrow leaf for about39.1%and16.7%. The narrow leaf is higher than the broad leaf, so the drought-enduring capacity of broad leaf is better than narrow leaf, only the drought-enduring method is different, which reflects that the broad leaf maintains the expansion pressure of cells mainly through the high concentration of solute or the solute accumulation, and the abilities to bear the drought and keep the moisture and narrow leaf mainly depend on the resilience and the water store ability of the cell wall.