The Hydraulic Drought-resistance Strategies Of Salix Psammophila And Caragana Korshinskii In Water/Wind Erosion Crisscross Region Of Northern Shaanxi

Plant hydraulic architecture is an important aspect of the research on plant water relations, it directly determine plant drought resistance and water use. In this paper, taking Salix psammophila and Caragana korshinskii growing in water/wind erosion crisscross region of northern Shaanxi as the materials, we explored the leaf water relations and photosynthesis, stem and root water transport efficiency and security, and the plasticity of water physiological traits of Caragana korshinskii under different habitats.The major objective was to reveal the physiological and ecological mechanisms of the two shrubs adapting to dry sandy habitats. The main results were as the follows:(1) Salix psammophila had higher leaf water potential and leaf water transport efficiency than Caragana korshinskii, but its leaves were more vulnerable to hydraulic dysfuntion than Caragana korshinskii, meanwhile,Salix psammophila reduced embolism in leaves through stricter stomatal regulation, thus maintained relatively larger hydraulic safety margin, suggesting that Salix psammophila belonged to water-spending species, and mainly adopted drought--avoidance strategies. Caragana korshinskii had higher leaf cell elastic modulus, osmotic regulation abilities, dehydration--resistance and stronger ability to resist embolism than Salix psammophila,implying that Caragana korshinskii leaves mainly adopted the conservative drought--tolerance strategy.(2) Salix psammophila had a relatively higher water transport efficiency in stems and roots, its stems and roots were also more vulnerable to embolism than those of Caragana korshinskii. The roots of the two shrubs had higher hydraulic efficiency and hydraulic vulnerability than stems. Salix psammophila stem had diurnal embolism repairing, but Caragana korshinskii stems and the roots of the two shrubs didn’t had that function, diurnal embolism and repairing might be an important mechanism for Salix psammophila to adapt to dry sandy habitat.(3) Higher hydraulic conductivity and vulnerability in Salix psammophila stems may be attributed to its longer maximum xylem vessel length, higher xylem vessel density, larger xylem vessel area /cross-sectional area, larger pit area / vessel wall and lower wood density when compared to Caragana korshinskii. Higher hydraulic conductivity and vulnerability in Salix psammophila roots may be related with its larger vessel diameter, higher xylem vessel area /cross-sectional area and lower wood density.(4) For the four habitats, slope top + aeolian sandy soil covering loessial sandy soil and gully + dam silt loess sandy soil had significantly higher average soil water content in 1~3m and 3m soil layer than those of slope+ loess-red clay and slope top + aeolian sandy soil. The crown size, height, and current-year twig lengh of Caragana korshinskii growing on slope+ loess-red clay and slope top + aeolian sandy soil significantly decreased, leaf thickness increased, midday leaf water potential, net photosynthetic rate, stomatal conductance and transpiration rate also significantly reduced. Among these parameters, current-year twig length, net photosynthetic rate, stomatal conductance and transpiration rate showed a larger plasticity.