Responses of jack pine (Pinus banksiana) seedlings to root zone pH and calcium

Plants growing in calcareous soils are exposed to high pH and elevated calcium levels which may reduce growth and produce high mortality in sensitive plants. In this study, we examined the hypotheses that in the high pH-sensitive jack pine (Pinus banksiana) seedlings, elevated root zone pH would reduce the ability of seedlings to control Ca uptake and the increase in Ca tissue concentrations would further aggravate the detrimental effects of high pH. We conducted two separate experiments to (i) investigate growth and physiological responses of jack pine (P. banksiana) seedlings to root zone pH ranging from 6 to 9, and (ii) examine the effects of 0.25 mM, 1 mM, 5 mM, and 10 mM Ca on physiological responses and nutrient uptake in jack pine seedlings exposed to the root zone pH of 6.5, 7.5, and 8.5 in nutrient solution culture. High root zone pH and high Ca concentrations significantly reduced growth, net photosynthesis, transpiration rates, needle chlorophyll concentrations, and root cortex cell lengths in seedlings. High root zone pH also decreased needle Ca and B concentrations, but the examined concentrations of Ca in nutrient solution had little effect on the needle composition of the examined essential elements including Fe, P, K, Cu, B, Mn, and Zn. We concluded that poor growth of conifer trees reported for calcareous soils is likely due to impaired root growth and the effects on gas exchange, likely caused by the reduced water uptake at high pH and elevated Ca levels.