Salt-related suppression of bud break in Populus trichocarpa: Cost of inclusion, ion-specific or osmotic effects?

Salt-laden winter storms cause bud failure or delayed bud break of coastal deciduous trees. In five experiments detached shoots of different genotypes of trees and shrubs were set to break buds in solutions of variable composition and concentration containing NaCl, KCl, K 2 SO 4 , CaCl 2 , Na 2 SO 4 , PEG and glycinebetaine to evaluate the effect of: 1) specific-ion stress, 2) osmotic stress and 3) osmotic adjustment on leaf expansion at bud break of black cottonwood (Populus trichocarpa). Ion-specific toxicity, osmotic effect or osmotic adjustments were not shown to affect leaf expansion growth. In solutions up to 80 mM neither sodium nor chloride was more detrimental than potassium or sulphate. Glycinebetaine did not alleviate salt stress but suppressed growth to the same degree as NaCl at 10 and 50 mM isoosmotic concentrations. Genotypes varied in vigour but all responded similarly to elevated concentrations of solutes. Leaf growth at bud break was found to decrease with rising solute concentration at constant osmotic potential of the external solution. The cost of inclusion of solute from the external solution was a likely explanation of the observed suppression of leaf growth.