Deep subsoil nutrient uptake in potassium-deficient, aggrading Pinus resinosa plantation

Growth of Pinus resinosa Ait. (red pine) on a potassium-deficient sandy soil at the Charles Lathrop Pack Demonstration Forest in Warrensburg, New York, is influenced by fine-textured lenses at 2-3 m below grade. A possible mechanism for an observed increase in surface soil potassium over time is nutrient uptake by red pine roots penetrating into these fine-textured, subsoil layers, and subsequent cycling of these nutrients between foliage and surface soil horizons. To test this hypothesis, we applied nutrient tracers directly to the deep subsoil and measured their uptake over several growing seasons: Strontium was applied in 1989 and 1993, while rubidium-free potassium (the Rb/K reverse tracer method) was applied only in 1993. Trees treated in 1989 had significantly greater concentrations of foliar and bud strontium than control trees, and trees treated only in 1993 also demonstrated significant uptake of potassium 2 years after treatment. These effects were present regardless of whether the trees had been surface-fertilized with potassium five decades earlier. The results demonstrate the importance of subsoil nutrient pools in forest ecosystem function.