Morphological and physiological responses of current sophora davidii seedlings to drought stress
白刺花幼苗对不同强度干旱胁迫的形态与生理响应

Sophora davidii, an endemic leguminous shrub, is a potential tool species for vegetation and ecosystem rehabilitation in the arid region of the upper reaches of the Minjiang River, southwest China. In order to assess the ability of tolerating drought in the species, we investigated the effects of drought stress on growth, biomass production and partitioning, water-use efficiency, leaf anatomical characteristics and photosynthetic pigment contents of S. davidii seedlings. Two-month-old seedlings were grown under water supply regimes of 100, 80, 60, 40 and 20% water-holding capacity (WHC), respectively, in an open-sided greenhouse. Leaf area, branch number, basal diameter, root length, root mass per soil volume, biomass production and WUE were the greatest in the seedlings of 100% WHC treatment, and they slightly declined in 80% WHC but were greatly reduced in 60%-40% WHC and were severely retarded by 20% WHC. As expected, drought induced an increase in root mass fraction and a decrease in leaf mass fraction, thereby maintaining a balance between water-losing and water-obtaining processes. Drought stress increased palisade mesophyll thickness while reduced spongy mesophyll thickness. Moreover, drought significantly increased Chla, Chlb, Chla+b, and carotenoid contents (Car), but decreased the ratios of Cha/b and Chl/Car. The results demonstrated that S. davidii seedlings avoid or tolerate drought by reducing branching intensity and leaf area while maintaining a high percentage of root mass and chlorophyll content in leaves. The fact that there was no mortality and leaf shedding in the seedlings even under 20% WHC condition indicates that this native N-fixing shrub species has a great potential for vegetation restoration in dry valleys of the Hengduan Mountain and other arid regions.