The Role of Leaf Area Development and Photosynthetic Capacity in Determining Growth of Kenaf under Moderate Salt Stress

Growth, net CO2 exchange rate and plant water relations were analysed in kenaf (Hibiscus cannabinus) cv. Cuba-108, a stem fibre crop, grown at 1, 37 and 75 mM NaCl. Dry weight was reduced only at 75 mM NaCl although leaf area was affected at both 37 and 75 mM NaCl. Growth analysis following nine serial harvests over 40 days showed a significant decline in leaf area ratio with salt stress but no decrease in net assimilation rate. CO2 exchange rate, measured on recently expanded leaves by infrared gas analysis, increased in plants grown at 37 mM NaCl and was unchanged at 75 mM NaCl. Pressure-volume analysis of plant water relations showed an osmotic adjustment of 0.15 MPa in plants grown at 75 mM but no adjustment at 37 mM NaCl. Turgor potential declined in plants grown at either salt level and fell to near zero during midday. We conclude that growth in kenaf under moderate salt stress is affected primarily through a reduction in expansive growth and leaf area development rather than a decline in photosynthetic capacity.