OZONE, ACIDIC PRECIPITATION, AND SOIL MG IMPACTS ON SOIL AND LOBLOLLY-PINE SEEDLING NUTRIENT STATUS AFTER 3 GROWING SEASONS

Recent studies have suggested that the growth of loblolly pine (Pinus taeda L.) has declined in the southeastern United States, possibly due to acidic deposition and air pollutants, especially under conditions of low nutrient availability. Consequently, the potential for individual and synergistic impacts of O3, acidic precipitation, and soil Mg status on the nutrient status of loblolly pine seedlings and soil was investigated over a 3 yr study period. Thirty-six open top chambers equipped with a rainfall exclusion/addition system were utilized to administer three levels of O3 (subambient, ambient, or twice ambient) and two acidic precipitation treatments (pH 3.8 or 5.2) to seedlings growing in 24-L plastic pots containing soil having either 35 or 15 mg kg-1 of exchangeable Mg. Each chamber contained 36 pots, and each treatment combination was replicated six times for a total of 1296 individual pots. After three seasons, throughfall and foliar nutrition data indicated that foliar leaching was not accelerated by increasing the acidity of precipitation from pH 5.2 to 3.8 and that increasing O3 did not act to exacerbate foliar leaching. Further, foliar nutrient concentrations were not significantly affected by precipitation pH or O3 treatments. Soil and soil solution data also indicate no accelerated soil leaching associated with chronic acidic precipitation. Differences in soil Mg treatments were reflected in soil solution and seedling Mg contents, but the 15 mg kg-1 soil Mg treatment was not sufficiently low enough to induce Mg deficiency in the seedlings.