Aluminum Effects on Northern Red Oak Seedling Growth in Six Forest Soil Horizons

Abstract

AbstractThe response of northern red oak (Quercus rubra L.) seedlings to varying levels of soil Al was examined in a 16‐wk greenhouse study. Forest soil samples representing three soil series were used as growth media: Captina (Fragiudult, Missouri), Lexington (Paleudalf, Mississippi) and Becket (Fragiorthod, New York). Soil from two horizons from each series was separately amended in four treatments to create a wide range of soil Al availability: (i) control, (ii) limed [Ca(OH)2], (iii) acidified (HCl), (iv) acidified with supplemental calcium added (+ HCl and CaSO4). Treatments significantly (p < 0.05) altered soil pH (range 3.65 to 5.48), base saturation, and 0.01 M SrCl2‐extractable Al (range 0.6–37.2 mg kg−1). Compared to controls, both acidification treatments resulted in significant reductions in fine root and foliar biomass production or in fine root branching, in all horizons except the highly organic Bhs of the Fragiorthod. In the remaining five horizons, fine root branching and biomass production were highly and negatively correlated (R2 = 0.70 and 0.50, respectively) with 0.01 M SrCl2‐extractable Al. Although fine root tissue concentrations of Al correlated highly with 0.01 M SrCl2‐extractable Al levels, root tissue Al predicted root branching and biomass only moderately well (R2 = 0.30 and 0.21, respectively). Fine root branching was more sensitive to treatment effects than either root biomass production or root elongation. Reductions in foliar biomass appeared to be secondary responses to direct effects on root systems. Present soil Al levels and acidic deposition rates appear to pose no threat to northern red oak in the southern portion of its range, whereas the possibility of Al toxicity in northeastern Spodosols deserves further study.