Studies On Photosynthesis And Water Physiology Of Populus Euphratica Oliv's Polymorphic Leaves

Populus euphratica Oliv is the only tree which could form a large area of natural forest in arid desert regions of Northwest China. Because of the long-term adaptation of the continental climate of extreme drought, the leaf shapes of P.euphratica were showed polymorphism. Perhaps, this particular phenomenon is a strategy of P.euphratica to adapt to the environmental changes, it's not only to ensure the survival of P.euphratica under the salt and drought stress, but also to make full use of high light intensity for photosynthesis. In order to understand the ecological adaptation mechanism of polymorphic leaves of P.euphratica, the photosynthetic characteristics, stomatal characteristics and water physiology of dentate broad-ovate leaves and lanceolate leaves from P.euphratica which grow in Beijing, Wuhai and Huhehaote were studied. To analysis the adaptation ability and to understand the ecological adaptation mechanism of polymorphic leaves of P. euphratica.1. The Pn of dentate broad-ovate leaves always higher than that of lanceolate leaves. Under normal condition, the light compensation point of dentate broad-ovate leaves and lanceolate leaves are 60μmolm-2s-1 and 75μmolm-2s-1, the light saturation point of both are higher than 1600μmolm-2s-1, dentate broad-ovate leaves'is higher. The diurnal change of Pn of these two kinds of leaves shows single peak curve, both of them could not reach the light saturation point under normal condition, and the highest Pn is at 11 am; the diurnal change of Tr and Gs of these two kinds of leaves is similar. The Tr of dentate broad-ovate leaves is higher than that of lanceolate leaves.2. The stomatal density, stomatal size, and stomatal opening rate at adaxial side are higher than that of at abaxial one in both of the two kinds of leaves. The Stomatal density and stomatal size of dentate broad-ovate leaves are higher than that of lanceolate leaves, the stomatal opening rate of dentate broad-ovate leaves is lower than that of lanceolate leaves, showed xerophytic structure. 3. The average hydraulic conductivity of branches with dentate broad-ovate leaves (6.61×10-5kgs-1MPa-1) is higher than that of lanceolate leaves (5.19×10-5kgs-1MPa-1).The reduction of hydraulic conductivity of dentate broad-ovate leaves (0.06×10-5kgs-1MPa-1) is obviously lower than that of lanceolate leaves (1.88×10-5kgs-1MPa-1) after water stress. The study showed that the hydraulic conductivity of dentate broad-ovate leaves is more stable than that of lanceolate leaves.4. The original osmotic pressure at full turgor, the osmotic pressure at zero turgor, and the difference of these two values of dentate broad-ovate leaves are lower than that of lanceolate leaves, which indicated that dentate broad-ovate leaves could keep their normal turgor under drought stress. Theεof lanceolate leaves (2.3597) is lower than that of dentate broad-ovate leaves (8.4324), which indicated that lanceolate leaves have a higher cell wall flexibility and a better turgor ability.The study showed that, the light energy efficiency and the water stress tolerance ability of dentate broad-ovate leaves are higher than that of lanceolate leaves, may be these changes are the results of leaves of P.euphratica to adapt to the environmental stress during development.