Growth, ion content and photosynthetic performance of salt-stressed kiwifruit plants

Rooted cuttings of kiwifruit (Actinidia sinensis P. cv Hayward) were grown in sand-perlite mixture (1:3), and irrigated with half-strength, recycled Hoagland nutrient solution, containing 0, 5, 10, 15, 20 and 30 mM of added NaCl. Growth, ion content and gas exchange response to salt treatment were examined over 60 days. Salinity led to reduced growth, although foliar symptoms of salt toxicity were absent. Plant dry weight and leaf area were reduced significantly with 10 mM NaCl in nutrient solution. Leaf expansion rate, leaf size and number of leaves per plant were affected by NaCl salinity. Sodium accumulated mainly in roots while chloride content in leaves and roots increased significantly above 10 mM NaCl. Photosynthetic rate (Pn) decreased with increased levels of leaf chloride. The decrease in photosynthesis was only partially due to stomatal closure. There was no reduction in intercellular CO sub(2) concentration (Ci) for salt-stressed leaves indicating that nonstomatal factors were contributing to the decrease of Pn. In conclusion the data indicate that kiwifruit is a salt sensitive plant and salinity affects its growth through reduction in leaf area development and decline in photosynthetic capacity.