Tamarack response to salinity: effects of sodium chloride on growth and ion, pigment, and soluble carbohydrate levels
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The extraction of bitumen from oil sands can increase levels of sodium and chloride in boreal forest soils. A study was designed to test the effect of 30 and 60 mmol/L NaCl on 6-month-old tamarack (Larix laricina (Du Roi) K. Koch.) seedlings grown in aerated nutrient solutions. After 40 days of treatment in a growth chamber, 30 mmol/L NaCl caused injury to old needles and decreased shoot biomass, root potassium concentration, root soluble carbohydrate content, as well as chlorophyll a, chlorophyll b, and carotenoid levels in old needles. Sodium content of seedlings exposed to 30 mmol/L NaCl was higher in roots than in stems and new needles, while chloride content was higher in both old and new needles. Sodium and chloride concentrations were similar in new needles and in old needles. Seedlings exposed to 60 mmol/L NaCl showed injury in both old and new needles and lower root and shoot biomass, root magnesium and potassium concentrations, and both root and stem soluble carbohydrate levels. Furthermore chlorophyll a, chlorophyll b, and carotenoid levels were lower in all needles than in the control. Sodium and chloride contents of seedlings treated with 60 mmol/L NaCl were higher in old and new needles than in roots and stems. The results suggest that tamarack seedlings have a moderate tolerance to salinity, and when exposed to 30 mmol/L NaCl the seedlings could avoid injury by maintaining a relatively high K+/Na+ ratio in new needles and controlling Na+ transport to the shoots.