GROWTH, PHYSIOLOGY, AND NUTRITION OF LOBLOLLY-PINE SEEDLINGS STRESSEDBY 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 E lectric Power Research Insitute are summarized here. The overall objec tive of the ROPIS program was to develop a general mechanistic theory of plant response to air pollutants and other stresses. Direct and ind irect phytotoxic impacts of O3 combined with induced deficiencies of k ey nutrients as a consequence of acidic deposition are important compo nents in many of the hypotheses used to explain reported declines in f orest growth. In order to address these concerns as they relate to lob lolly pine (Pinus taeda L.) growth and develop a greater level of mech anistic 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 O3; an d (ii) determine the underlying physiological and edaphic basis for lo blolly growth response to O3, acidic precipitation, and soil Mg status . An open-top chamber facility located at Oak Ridge, TN provided contr olled O3 exposure for the genotype screening study (1986-88) and contr olled O3 exposure and rainfall exclusion and addition for the O3-rainf all acidity-soil Mg interaction study (1987-89). A variety of experime ntal techniques, measurements, and statistical procedures were used ov er a 4-yr period to quantify various aspects of plant growth, physiolo gy, and soil-plant relationships. Results from the genotype screening study indicate that although family-specifiC O3 effects were observed at the end of the first year, no statistically significant O3 effects on diameter, height, or total biomass were evident at the end of three growing seasons; nor were any significant O3-family interactions foun d. In the interaction study, rainfall acidity and soil Mg level had on ly minimal affects on seedling growth and physiology. Ozone exposure p roduced significant changes in many variables, the most important bein g a net retention of carbon in above-ground biomass and a subsequent r eduction in carbon allocation to the root system. This change could ha ve important longterm implications for the tree's ability to obtain wa ter and nutrients, maintain important rhizosphere organisms, and achie ve a level of vigor that protects against disease and insect attack.