AMONG-AND WITHIN-PROVENANCE VARIABILITY OF PINUS PONDEROSA (PINACEAE) SEEDLING RESPONSE TO LONG-TERM ELEVATED CO₂ EXPOSURE

Among-and within-provenance variability in growth and physiological performance were investigated in Pinus ponderosa Dougl. ex P. Laws, seedlings subjected to ambient or elevated carbon dioxide (ambient + 175 μLL⁻¹ or ambient + 350 μLL⁻¹ CO₂) for 16 months. Among-provenance variability was studied with bulk-collection sources from 5 different physiographic regions of California. Within-provenance variability was investigated with three half-sibling families from a common physiographic locale. Regardless of source, stem volume increased at ambient + 175 μLL⁻¹ CO₂, but further increase in CO₂ to ambient + 350 μLL⁻¹ resulted in a variety of stem volume responses with about equal numbers of sources showing either no change or slight increases. Physiological responses to elevated CO₂, including decreased efficiencies of photochemical transfer (Fv/Fm), no change in stomatal conductance, and increased photosynthesis and water-use efficiency, were consistent among half-sibling families. Thus, for this limited survey, there was little evidence for within-provenance variation in physiological response to elevated CO₂. Among-and within-provenance variability in growth response to CO₂ suggests differing genetic control of carbon acquisition and allocation mechanisms among sources of P. ponderosa. Understanding the extent and sources of intraspecific variation in growth and physiological responses to elevated CO₂ is a critical need in developing management strategies that account for future altered environments.