Growth, physiology, and nutrition of loblolly pine seedlings stressed by ozone and acidic precipitation : a summary of the ropis-south project

Previously published results from a multidisciplinary research program, Response of Plants to Interacting Stress (ROPIS), initiated by the Electric Power Research Institute are summarized here. The overall objective of the ROPIS program was to develop a general mechanistic theory of plant response to air pollutants and other stresses. Direct and indirect phytotoxic impacts of O sub(3) combined with induced deficiencies of key nutrients as a consequence of acidic deposition are important components in many of the hypotheses used to explain reported declines in forest growth. In order to address these concerns as they relate to loblolly pine (Pinus taeda L.) growth and develop a greater level of mechanistic understanding of stress response, a study was formulated with two major objectives: (i) over a multi-yr period evaluate the role of loblolly pine genotype in governing loblolly growth response to O sub(3); and (ii) determine the underlying physiological and edaphic basis for loblolly growth response to O sub(3), acidic precipitation, and soil Mg status. An open top chamber facility located at Oak Ridge, TN provided controlled O sub(3) exposure for the genotype screening study (1986-88) and controlled O sub(3) exposure and rainfall exclusion and addition for the O sub(3)-rainfall acidity-soil Mg interaction study (1987-89). A variety of experimental techniques, measurements, and statistical procedures were used over a 4-yr period to quantify various aspects of plant growth, physiology, and soil plant relationships. Results from the genotype screening study indicate that although family-specific O sub(3) effects were observed at the end of the first year, no statistically significant O sub(3) effects on diameter, height, or total biomass were evident at the end of three growing seasons; nor were any significant O sub(3)-family interactions found. In the interaction study, rainfall acidity and soil Mg level had only minimal affects on seedling growth and physiology. Ozone exposure produced significant changes in many variables, the most important being a net retention of carbon in above-ground biomass and a subsequent reduction in carbon allocation to the root system. This change could have important longterm implications for the tree's ability to obtain water and nutrients, maintain important rhizosphere organisms, and achieve a level of vigor that protects against disease and insect attack.