Foliar nutrient dynamics and nutrient-use efficiency of oak and pine on a low-fertility soil in Wisconsin

Abstract

Seasonal changes in 10 nutrients were investigated in the foliage and current twigs of jack pine (Pinusbanksiana Lamb.) and northern pin oak (Quercusellipsoidalis E.J. Hill) growing on a sandy, nutrient-poor soil in northwestern Wisconsin. Midsummer (July 26) concentrations of all nutrients except Zn were significantly greater in oak foliage than in current needles of pine. Whereas the absolute amounts of N, P, K, Mg, S, B, and Fe in oak foliage peaked in midsummer, generally in late July, the amounts of Ca, Zn, and Mn continued to increase until leaf abscission. The absolute amounts of all 10 nutrients in current needles of pine increased over the growing season. Absolute amounts of nutrients in 2- and 3-year-old needles generally decreased from midsummer to leaf abscission. The two species differ in mechanisms of nutrient-use efficiency. Northern pin oak has a greater requirement for all macronutrients except Mg than jack pine. Although the absolute amounts are greater, proportionally lower amounts of required nutrients are retained in perennial tissues of northern pin oak than in jack pine. A large portion of the nutrient requirement in oak is met by recycling of nutrients contributed by litterfall, throughfall, and fine-root turnover. Northern pin oak resorbed greater amounts of N and K prior to leaf abscission than jack pine. In contrast, jack pine conserves nutrients by investing low amounts of nutrients per unit of leaf or bolewood production and by returning a low proportion of nutrients in litterfall per unit aboveground tissue produced.