Leaf development, transpiration and ion uptake and distribution in sugarcane cultivars grown under salinity

Abstract

The effects of salinity on leaf growth, initiation and senescence, on transpiration rates, on leaf water potential and on uptake and distribution of several ions were studied in two sugarcane cultivars differing in salinity sensitivity. Plants, growing in a growing mixture in pots, were exposed to salinized irrigation water for 68 days, starting 60 days after planting. EC values of the irrigation water were 1.0, 2.0, 4.0, 8.0 and 12 dS/m, obtained by using a mixture of NaCl and CaCl2. Plants were also grown in nutrient solution and were at a similar age when exposed to a salinity level of 3 dS/m for 30 days followed by 6.0 dS/m for an additional 30 days. Two Na:Ca ratios of 18:1 and 1:2 were used for salinization of the nutrient solution. Both leaf dry weight and area decreased with increasing salinity, but in the more salinity tolerant cultivar H69-8235, the decrease was moderate. Salinity hardly reduced average area per leaf in H69-8235, while the number of leaves declined sharply. This decline was caused by enhanced senescence of mature leaves and not by a decreased rate of leaf initiation. In the more sensitive cultivar, H65-7052, leaf area and initiation of new leaves were sharply reduced by salinity while leaf senescence was less affected. Leaf water potential decreased during the early stages of salinity exposure, and the reduction in water potential was larger in H69-8235. Salinity also decreased the rate of transpiration rate but to a lesser extent than leaf development and growth. The accumulation of Cl and Na in the TVD (top visible dewlap) leaf of the tolerant cultivar H69-8235 was greater than in the sensitive cultivar H65-7052. The concentration of Cl in the TVD leaf was more than 10 times that of Na in both cultivars. The concentration of both ions, but not of K, increased during the early stages of salinity exposure and then remained constant. A gradient in concentration of Cl and Na over the plant was found in both cultivars at all salinity levels, and was steepest between the TVD and younger leaves. No specific Na effect on leaf growth or transpiration could be detected. The accumulation of Cl and Na but not of K occurred primarily in the roots rather than in the leaves and stalks.