Drought tolerance characteristics of black spruce (Picea mariana) seedlings in relation to sodium sulfate and sodium chloride injury

This study examined the feasibility of using water relations to screen black spruce (Picea mariana (Mill.) BSP) planting stock for salt tolerance, prior to planting in saline oil sands tailings. To do so, water relations parameters were derived from pressure–volume curves for individual seedlings prior to salt stress treatments. Pressure–volume curves were constructed for branches removed from the seedlings and the seedlings were subsequently treated with 60 mM NaCl, 120 mM NaCl, or 90 mM Na2SO4 in solution culture. After 2 weeks of treatment, seedlings treated with NaCl solutions had greater needle electrolyte leakage and visible needle injury compared with equimolar and iso-osmotic solutions of Na2SO4, suggesting that chloride played a role in needle injury. At turgor loss point, a more negative osmotic potential was significantly correlated with lower electrolyte leakage in seedlings treated with Na2SO4 but not in those treated with NaCl. The results suggest that, in contrast with NaCl, Na2SO4 injury to black spruce seedlings may be largely due to osmotic stress and that drought tolerance parameters may be more helpful in predicting salt tolerance in plants treated with Na2SO4 than in those treated with NaCl.Key words: osmotic stress, salt stress, drought tolerance, water relations, ion toxicity, black spruce.