NaCl and Na2SO4 alter responses of jack pine (Pinus banksiana) seedlings to boron

Using sand culture, we examined the responses of 6-month-old jack pine (Pinus banksiana Lamb.) seedlings to boron and salinity (sodium chloride and sodium sulfate) treatments. During 4 weeks of treatments, 60 mM NaCl and 60 mM Na₂SO₄ significantly decreased survival, new shoot length, number of new roots, shoot to root dry weight ratio and transpiration rates. When applied in absence of the salts, B had little effect on the measured variables. However, when applied together with salts, B decreased seedling survival, increased needle injury and altered tissue elemental concentrations in jack pine seedlings. In 2 mM B treatment, B concentration was higher in the shoots than in the roots. However, when 2 mM B was present in NaCl and Na₂SO₄ treatments, shoot boron concentration declined and greater proportion of B accumulated in the roots. This shift corresponded to a decline in transpiration rates. In plants treated with NaCl, Na accumulated primarily in the shoots, while in Na₂SO₄-treated plants Na accumulated mostly in the roots. Based on the electrolyte leakage and needle necrosis data, Cl^– appears to be the major factor contributing to seedling injury and B aggravates the injurious effects of NaCl. We suggest that Cl^– may contribute to Na and B toxicity in jack pine by altering cell membrane permeability leading to increased Na concentration in the shoots.