Hydraulic characteristics of Lycium barbarum L. seedlings under drought stress and re-watering conditions

Lycium barbarum L. is the main commercial crop across the arid lands in northwestern China, which is drought resistant with various functions, such as soil improvement, soil fertility enhancement. To determine water transport characteristics and increase the potential for agricultural productivity of L. barbarum, we conducted a pot experiment at the agricultural demonstration site in Gulang, Gansu Province (37.09°N, 102.79°E). The experiment consisted of 3 treatments — normal water application (N), moderate drought (M) and severe drought (S). The hydraulics characteristics of the canopy and root, photosynthetic rate (P_n) and stomatal conductance (G_s) were monitored in 2-year-old seedlings of 'Ningqi 1', 'Ningqi 5' and 'Mengqi 1' varieties of L. barbarum during drought stress. The effect of re-watering after drought stress on the hydraulics characteristics of the shoot system was determined in the study. The results showed that hydraulic conductance of canopy, shoot and root gradually declined with increasing drought stress. Also hydraulic conductance of the plant decreased with increasing degree of drought stress and the ratio of root to plant (R_root/R_plant) hydraulic conductance resistance increased the most in 'Ningqi 5'. It was also noted that the canopy equation of xylem embolism vulnerability curve in L. barbarum seedlings and xylem water potential loss of hydraulic conductance was 50% in 'Ningqi 1', significant higher than those in 'Ningqi 5' and 'Mengqi 1'. Also there was a statistically significant correlation (P < 0.05) among specific hydraulic conductance of leaf (K_{l, leaf}) and stomatal conductance (G_s) as well as photosynthetic rate (P_n) of leaf of L. barbarum. The growth of plants after drought stress was largely determined by the ability of root system to absorb water following re-watering after 4 days of drought stress. The recovery of hydraulic conductance was fastest with the most obvious compensation effect of water transportation for 'Mengqi 1' and the slowest hydraulic conductance recovery for 'Ningqi 5'. The results suggested that drought-tolerate characteristics was associated with hydraulic conductance in L. barbarum. Hydraulic sensitivity of root to drought stress reflected a continuous capacity of plant to resist drought. The ability of the root system to recover from drought stress and compensation effect was critical for plant soil water utilization under adverse conditions. It was important to regulate the hydraulic conductance of roots for improvement of soil water use efficiency.