OZONE, ACIDIC PRECIPITATION, AND SOIL MG EFFECTS ON GROWTH AND NUTRITION OF LOBLOLLY-PINE SEEDLINGS

Height, diameter, biomass, and nutrient concentration and content were determined for loblolly pine (Pinus taeda L.) seedlings grown at two levels of soil Mg and exposed to chronic levels of O3 and simulated acidic precipitation. Nutrient contents in precipitation and throughfall were also determined. Seedlings were planted in a sandy loam soil (Lilly series) having approximately 15 or 35 mg/kg Mg and were exposed to subambient, ambient, or twice ambient concentrations of O3 in open-top chambers from May through to October of 1987 and April through to October of 1988. Seedlings also received simulated rainfall at pH 3.8 or 5.2 in volumes equivalent to ambient rainfall. After two growing seasons, height and diameter were significantly greater for seedlings exposed to subambient and twice ambient O3 than for seedlings exposed to ambient O3. Biomass of all seedling components was progressively reduced with increasing O3 concentrations. Net throughfall nutrient contents and foliar nutrient contents were not significantly affected by precipitation pH treatments, indicating that foliar leaching was not accelerated by increasing the acidity of precipitation from pH 5.2 to 3.8. Throughfall and foliar nutrient contents were not significantly affected by O3 treatments, and no significant O3 x precipitation pH interactions occurred, indicating that after two growing seasons O3 did not act to exacerbate foliar leaching. Seedlings grown in soil having 15 mg/kg Mg exhibited significantly reduced Mg concentrations and contents in all components, but seedling growth was not significantly affected by this treatment.