Response of Radiata Pine to Salt Stress. I. Water Relations, Osmotic Adjustment and Salt Uptake

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Abstract
Transpiration, total needle water potential and osmotic water potential, and proline concentration in needle sap were determined in radiata pine (Pinus radiata D. Don) seedlings subjected to a step- wise decrease in osmotic potential of their liquid rooting medium by addition of CaCl2 or NaCl (absorbable), or PEG 4000 (non-absorbable). Resultant concentrations of N, P, K, Mg, Ca, Na, and Cl were determined in needle, stem, and root tissue as well as in expressed needle sap. Seedling damage resulting from salt treatment was not due to water stress. CaCl2 caused greater damage than iso-osmotic concentrations of NaCI, and the damage was associated with Cl excess and an induced P deficiency. Seedlings rapidly salinized with NaCl rapidly and continuously absorbed ions into their needle sap until death, whereas those more slowly salinized appeared able to keep absorption to a lower level and escape visible injury. Proline accumulated in needle sap under both water and salt stress. Proline accumulation under salt stress could not be explained in terms of water stress alone. Radiata pine seedlings appeared better adapted to avoid rather than tolerate high ion concentrations in their living tissues.

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