We studied the effects of 0.5, 1 and 2 mM boron (B) on growth, water and nutrient uptake in 6-month-old jack pine ( Pinus banksiana) seedlings. After 6 weeks of treatment, B did not significantly affect survival and the measured growth parameters in jack pine. However, B-treated seedlings exhibited needle tip necrosis that progressed toward the bases of the needles in high concentration treatments. The visible needle injury was accompanied by an increase in electrolyte leakage from the needles and B accumulation in needles. The needles of plants treated with 2 mM B contained three-fold higher concentration of B than with the roots. In plants treated with B for four 10 and 6 weeks, stomatal conductance was reduced with a concomitant reduction in a steady-state root water flow. However, tissue concentrations of essential elements including K, P, Ca, Mg, and S were not altered by the B treatments. Therefore, water transport did not appear to affect uptake and distribution of mineral nutrients in jack pine and the observed needle necrosis and electrolyte leakage could be explained by B accumulation in the needles. Although photosynthetic pigments and the measured growth parameters were not altered by the 6-week B treatments, long-term growth effects should be anticipated due to effect of B on water relations. Read less