Ecophysiological differences among growth stages of Quercus laevis in a sandhill oak community
Plants in the sandhill habitats of the southeast are thought to be limited by soil resources such as water and nutrients. We measured ecophysiological characters related to resource use for several growth stages: Seedling Sprouts (small sprouts from small root collars), Stump Sprouts (small sprouts from large root collars) and Adults (large reproductively mature trees) of Quercus laevis (turkey oak) in SC. Adults did not differ from Stump Sprouts in water potentials, photosynthesis, stomatal conductance, or leaf nitrogen. In contrast, Seedling Sprouts differed from Stump Sprouts and Adults in June: lower predawn water potentials, lower rates of photosynthesis and stomatal conductance, higher specific leaf area, and lower leaf N concentration. The September growth stages rankings for these characters were generally similar to those in June, but variation within a growth stage was greater and thus Seedling Sprouts were only significantly different from the other two growth stages for leaf nitrogen. The differences between Seedling Sprouts and larger individuals may be due to differential access to soil resources as a function of rooting depth. Soil water availability was high in March, low in June, and higher again in September except at 1.25 m. Soil total N was higher at soil depth of 0-0.1 than 0.1-0.2 m in March, but did not differ between 0.25, 0.50, 0.75, 1.00 and 1.25 m in June. The differences in resource acquisition and resource use should relate to growth and survival of individuals within a population.