Abstract: Caragana korshinskii is widely used for sand-binding in Shapotou, Ningxia, China. Ii has adapted well to the habitat during the establishment. With the increasing age and the consumption of available soil water, the initially-planted C. korshinskii had degraded. To examine the relationship between the shrub age and the population degradation, we conducted field experiments on different-aged C. korshinskii (25-, 13- and 3-year-old) for the measurements of leaf water potential, leaf relative water content, leaf-specific apparent hydraulic conductance, photosynthetic rate and water use efficiency. We analyzed the relationships between photosynthetic properties and leaf water potential among the different-aged shrubs. The results showed that the photosynthetic capacities of young-mature and juvenile were higher than those of old-growth, while their water use efficiencies were lower compared to old-growth. The nonlinear relationships between both net assimilation rate (A) and stomatal conductance (G_s) with leaf water potential (Ψ) show that different-aged C. korshinskii plants adopt different drought response strategies. Juveniles reduce water loss through closing stomata, while older C. korshinskii plants respond to drought by adjusting WUE. Although the old-growth C. korshinskii maximized water use by increasing the WUE, the decreased photosynthesis and plant water potentials would slow the growth of plants and lead to their degradation.

Key words: Caragana korshinskii, shrub age, photosynthetic rate, water use efficiency