Effects of soil fertility and time on the leaf physiology of sugar maple in relation to forest decline

Two studies were conducted to assess physiological responses of declining sugar maple (Acer saccharum Marsh.) in southern Quebec to wet acidic precipitation and increased soil fertility. Leaves of sugar maple were relatively acidic, had low external neutralization capacity (ENC = 5.1 $ mu$equiv. H$ sp{+} rm g sp{-1}$) and buffering capacity index (BCI = 103 $ mu$equiv. H$ sp{+} rm g sp{-1}$), and higher ENC/BCI compared to three other tree species. Deciduous species showed a higher BCI and a lower ENC in August. Our results suggest that sugar maple may be relatively sensitive to wet acidic deposition and that leaf buffering capacity is related to photosynthesis potential and seasonal change in foliar Ca concentration. Foliar analyses revealed that fertilization with a mixture of K, Ca, and Mg had significant effects on leaf concentrations of K, free amino acids (FAA) and the ratios of N to K, and FAA to N after two growing seasons. Our results suggest that base cation fertilization improved the N and K status of sugar maple and that leaf carbon partitioning appeared to be more dynamic in fertilized trees