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

The effects of salinity on leaf growth, initiation and senescence, on trans piration rates, on leaf water potential and on uptake and distribution of s everal ions were studied in two sugarcane cultivars differing in salinity s ensitivity. Plants, growing in a growing mixture in pots, were exposed to s alinized 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, obtaine d 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 ra tios of 18:1 and 1:2 were used for salinization of the nutrient solution. B oth leaf dry weight and area decreased with increasing salinity, but in the more salinity tolerant cultivar H69-8235, the decrease was moderate. Salin ity hardly reduced average area per leaf in H69-8235, while the number of l eaves declined sharply. This decline was caused by enhanced senescence of m ature leaves and not by a decreased rate of leaf initiation. In the more se nsitive cultivar, H65-7052, leaf area and initiation of new leaves were sha rply reduced by salinity while leaf senescence was less affected. Leaf wate r potential decreased during the early stages of salinity exposure, and the reduction in water potential was larger in H69-8235. Salinity also decreas ed the rate of transpiration rate but to a lesser extent than leaf developm ent and growth. The accumulation of Cl and Na in the TVD (top visible dewla p) 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 1 0 times that of Na in both cultivars. The concentration of both ions, but n ot of K, increased during the early stages of salinity exposure and then re mained constant. A gradient in concentration of Cl and Na over the plant wa s 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 transpi ration could be detected. The accumulation of Cl and Na but not of K occurr ed primarily in the roots rather than in the leaves and stalks.