Effects of salt stress on the root growth and leaf water use efficiency of cucumber seedlings
盐胁迫对黄瓜幼苗根系生长和水分利用的影响

By the method of water culture, and with the seedlings of two cucumber cultivars having different tolerance to salt stress as test materials, this paper studied their root growth, vitality, and membrane permeability, as well as their leaf growth, transpiration rate (Tr) , relative water content (RWC) , and water use efficiency (WUE) under effects of different NaCl levels. The results showed that under salt stress, the absorption surface area of root was declined, whereas its membrane permeability was increased significantly. The leaf number per cucumber seedling was decreased, compared with that of the control. Both Tr and RWC were markedly decreased after 2 days exposure to salt stress. During the period of salt treatment, root vitality and leaf WUE were increased initially, but decreased then. For the salt-susceptible cultivar Jinchun No. 2, the decrement of its root vitality was 18.01% , 12. 17% and 10. 95 % higher than that of the salt tolerant cultivar Changchun Mici on the 9th day exposure to 50, 75 and 100 mmol x L(-1) NaCl, and the decrement of its leaf WUE was 2. 74% , 5. 27% and 0. 23 % higher than that of Changchun Mici on the 8th day exposure to 50, 75 and 100 mmol x L(-1) NaCl, respectively. Under short-term salt stress, the absorption capacity of root was raised to compensate its reduced absorption surface area, while the decrease of Tr and the increase of WUE could reduce the leaf water loss, which alleviated the imbalance between water demand and need and improved the salt-tolerance of cucumber seedlings. After 5 days exposure to salt stress, both root vitality and leaf WUE decreased, which showed more severe water imbalance. It could be concluded that the decrease of root absorption capacity was one of the main reasons of water imbalance, and the decrease of leaf WUE was one of the responses to water imbalance. Both the absorption capacity of root and the WUE of leaf were closely related to the salt-tolerance of cucumber cultivar.