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.