Elevated root zone pH and NaCl leads to decreased foliar nitrogen, chlorophyll, and physiological performance in trembling aspen (Populus tremuloides), green alder (Alnus alnobetula), tamarack (Larix laricina), and white spruce (Picea glauca)

Key message: Elevated root zone pH and NaCl caused a similar physiological response in all species tested. This may be a result of a deliberate stunting of growth. Abstract: Surface mining for bitumen in the Athabasca oil sands region of Northern Alberta involves the removal of all vegetation and soil from native boreal forest lands. Revegetation is challenging because reclamation sites have soils with elevated pH and NaCl levels. In the present study, trembling aspen, green alder, tamarack, and white spruce were grown in liquid culture and subjected to treatments with three pH levels (5, 7, 9) and three NaCl levels (0, 30, 60 mM) in a factorial design. After 50 days of treatment, total dry weight, gas exchange, foliar elemental, and chlorophyll concentrations were measured. Trembling aspen exhibited less than 50% survival for all pH 9 treatments, whereas green alder was sensitive to any increases in pH or NaCl. Tamarack and white spruce showed high survival and tolerance to pH levels of 9 and NaCl levels of 60 mM. However, some decreases in physiological variables were observed. All species showed decreases in total dry weight, foliar nitrogen and chlorophyll concentrations, net photosynthesis, and transpiration rates from elevated root zone pH and NaCl levels, potentially due to a deliberate downregulation of metabolism. Also, measuring chlorophyll concentration may provide a reliable indicator of seedling health. This study recommends reclamation sites with moderately high soil pH and NaCl be planted with trembling aspen, tamarack, or white spruce. Overplanting of trembling aspen may be needed to compensate for anticipated lower survival rates at pH 9. Biostimulants, such as beneficial bacteria, biochar, mycorrhizal fungi, and seaweed extracts, may be useful in reversing symptoms of plant stress.