Ozone, acidic precipitation, and soil Mg effects on growth and nutrition of loblolly pine seedlings

Abstract Height, diameter, biomass, and nutrient concentration and content were determined for loblolly pine ( Pinus taeda L.) seedlings growth at two levels of soil Mg and exposed to chronic levels of O 3 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 O 3 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 O 3 than for seedlings exposed to ambient O 3 . Biomass of all seedling components was progressively reduced with increasing O 3 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 O 3 treatments, and no significant O 3 × precipitation pH interactions occurred, indicating that after two growing seasons O 3 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 comonents, but seedling growth was not significantly affected by this treatment.