Red spruce and loblolly pine nutritional responses to acidic precipitation and ozone Original Research Article

A multidisciplinary research program called Response of Plants to Interacting Stresses (ROPIS) was initiated by the Electric Power Research Institute in 1986 to develop a general mechanistic theory of plant response to interacting air pollutants and other stresses. As part of the program, the individual and combined impacts of acidic precipitation and elevated O3 on nutritional responses of red spruce (Picea rubens Sarg.) and loblolly pine (Pinus taeda L.) were evaluated. Red spruce saplings were exposed to charcoal filtered, non-filtered, 1•5 times ambient or twice ambient levels of O3 in combination with rain pH treatments of 3•1, 4•1, or 5•1 for 4 years. Similarly, loblolly pine seedlings were exposed to subambient, ambient or twice ambient O3 levels in combination with acidic precipitation treatments of pH 3•8 or 5•2 for 3 years. Cation leaching was accelerated in the pH 3•1 rain treatment in the red spruce study, driven by atmospheric inputs of H+ and SO42−. Subsequent decreases in soil pH, exchangeable pools of Ca2+ and Mg2+, and increases in exchangeable Al3+ in the organic horizon were observed. Calcium and Mg2+ fluxes in throughfall of red spruce were also enhanced at pH 3•1, and foliar concentrations of Mg2+ were reduced. In contrast, soil pH and nutrient concentrations as well as foliar leaching in the loblolly pine study were not significantly affected by either the pH 3•8 or 5•2 rain treatments. Ozone exposure had no effect on throughfall or soil solution ionic flux for either species. Results indicate that ambient rainfall acidities are not likely to affect the nutritional status of loblolly pine. High elevation red spruce forests, however, could be impacted by acidic deposition via enhanced soil acidification, leading to Al3+ mobilization and reduced availability of important base cations as well as increased foliar leaching.