Population Differences In Responses To Water And Fertilization Supply In Populus Przewalskii Maxim

Water deficit is the critical factor which constraints tree production in arid and semi-arid regions, especially in northern, northwestern China, inner-Mongolia and Qinghai-Tibet plateau. Considering that poplars distribute widely with high adaptability and grow rapidly with large production in these regions, it is most important to investigate how poplars respond to drought stress environment. In this experiment, we used two contrasting populations of Populus przewalskii Maxim., which were from dry and wet climate regions respectively, as model plants to study the population differences in growth, morphological, physiological and biochemical responses to different watering and fertilization regimes. The results are as follows: 1. Drought stress significantly affected the growth, morphological, physiological and biochemical properties of two contrasting populations. Some properties decreased significantly by drought stress, such as height, basal diameter, total biomass, leaf area, net photosynthesis rate, transpiration rate and stomatal conductance; on the other hand, drought stress increased some properties, such as fine root/total root ratio, leaf abscisic acid content, instantaneous water use efficiency and carbon isotope composition. In addition, leaf relative water content reduced and the activity of peroxidase increased under drought stress. 2. Significant population differences of P. przewalskii cuttings were observed in plant growth and physiological properties under both well-watered and drought stressed treatments. Compared with the wet climate population, the dry climate population had smaller height, basal diameter, total biomass, leaf area and fine root/total root ratio, and higher net photosynthesis rate, transpiration rate, stomatal conductance, instantaneous water use efficiency and leaf abscisic acid content as effected by drought stress. 3. These morphological and physiological adaptations to water availability showed that the different populations may employ different survival strategies under drought stress at the initial phase of seedling growth and establishment. The dry climate population exhibited a conservative water use strategies with higher drought tolerance, while the wet climate population possessed a prodigal water use strategy with lower drought tolerance. These differences in drought responses may be used as criteria for genotype selection in different climate regions. 4. Watering, fertilization and their interaction affected the performance of P. przewalskii cuttings in growth, morphology and physiology properties. With the decrease of water and fertilization availabilities, plants allocated more dry matter into root. Under well-watered treatment, fertilization improved plant growth and gas exchange such as height, basal diameter, total biomass, leaf area and net photosynthesis rate, however, fertilization inhibited these properties under drought stress. Moreover, fertilization increased instantaneous water use efficiency under both watering regimes.