SENSITIVITY OF TREE SEEDLINGS TO ALUMINUM .3. RED SPRUCE AND LOBLOLLY-PINE

Unexplained declines in the growth of both red spruce (Pica rubens Sarg.) and loblolly pine (Pinus Taeda L.) have been reported within their natural ranges recently. The possible role of Al phytotoxicity as a causal agent in these declines has been studied extensively. Results of experiments with seedlings grown in solution, sand, and soil indicate minimal involvement of Al in the decline of loblolly pine. However, both controlled studies and field data indicate that reductions in tissue Ca and Mg may occur at Al concentrations well below those causing direct injury. Thus, Al may be involved in reductions in pine growth through interference with nutrient uptake and translocation. Several independent studies demonstrate that Al does directly affect growth of red spruce seedlings at Al concentrations of ≤0.25 mM, a concentration that might approach the range of soil solution. Al concentrations measured in native red spruce stands in the Appalachian Mountains (0.1-0.28 mM). In these seedling studies, concentration of Ca and Mg in red spruce roots and foilage were also markedly reduced by relatively low solution Al concentrations. Thus, a contributing role for Al phytotoxicity in red spruce decline, through both direct biomass reduction and indirect effects due to interference with nutrient uptake, appears plausible.