Water relations, hydraulic conductance, and vessel features of three Caragana species of the Inner Mongolia Plateau of China

摘要

From early May to late September 2005, diurnal and seasonal changes in water relations, hydraulic conductance, vessel features, photosynthesis (DCA), transpiration (DCE), and water use efficiency (WUE) were studied in the field for three Caragana species—C. microphylla Lam, C. davazamcii Sancz and C. korshinskii Kom—growing in different habitats in the Inner Mongolia Plateau of China. The three species were generally exposed to severe environmental drought during most of the growing period. Among them, C. korshinskii had the largest vessels and specific hydraulic conductivity (K_s) in one-year-old twigs while the lowest were recorded in C. microphylla. All three species had the highest Ks in the summer and the lowest in the spring. For the three species, the best leaf water status occurred in the autumn indicated by the largest diurnal mean leaf water potential (￥L) and the lowest leaf relative water deficit (RWD) while the severest leaf water stresses occurred in the spring. Caragana microphylla had larger WL than the other two species, and the lowest WL as well as the largest RWD occurred in C. korshinskii. The lowest RWD were found in C. davazamcii. The three species had the largest DCA and DCE in the autumn while the lowest values occurredin the spring for C. microphylla and C. davazamcii. Caragana korshinskii had the lowest DCA and DCE in the summer, which resulted in a decrease in soil water loss. Leaf stomatal conductance (gs) and transpiration rate (E) were found to be correlated to hydraulic conductance in soil-leaf continuum (Gt) more closely than Ks in one-year-old twigs. Generally, the seasonal changes in Gt were in accordance with those of DCA and DCE, with the exception of C. davazamcii, which had the largest Gt in the spring.Among the three species, C. davazamcii had the highest values of seasonal mean DCE and Gt, and the lowest drought resistance during the growing period, which was in line the higher soil water content in its habitat. In the spring, despite the high soil water content, C. microphylla had the greatest resistance to the leaf water deficit raised by the low Gt. In the autumn, the greatest drought resistance occurred in C. korshinskii, which was exposed to the severest water stress due to low soil water content. By analyses of seasonal changes of K_s and G_t as well as their relationships with leaf gas exchange, G_t was approved to be more important than specific subportions (one-year-old twigs in this study) in terms of leaf water supply.