PROCEEDINGS: Index of Abstracts

THE CHRONIC RESPONSE OF YELLOW-POPLAR AND EASTERN WHITE PINE TO OZONE AND ELEVATED CARBON DIOXIDE: THREE-YEAR SUMMARY

Joanne Rebbeck

USDA Forest Service, Northeastern Forest Experiment Station, 359 Main Road, Delaware, OH 43015.

Abstract: The objective of this study was to determine the long-term effects of ozone (O₃) and carbon dioxide (CO₂) on the growth and physiology of eastern white pine (Pinus strobus) and yellow-poplar (Liriodendron tulipifera) under plantation conditions. Two separate plantations of each species were established in Delaware, Ohio, in 1991 and 1992. Seedlings were fumigated from mid-May to mid-October in 1992, 1993, and 1994 in standard 3m diameter open-top chambers. The treatments, each replicated three times in a randomized block design, included charcoal-filtered air (CF), 1X ambient O₃ (1X), 2X ambient O₃ (2X), 2X ambient ozone plus 350 ppm CO₂ above ambient (2X+CO₂), and open-air (OA) chamberless plot. Monthly growth and physiological measurements taken during each growing season included stem height and basal diameter, photosynthesis, stomatal conductance, chlorophyll content, and foliar nitrogen and phosphorus concentration. Subsamples of yellow-poplar were destructively harvested in 1993. First-season exposure to O₃ plus CO₂ appeared to have a stimulatory effect on the growth of both species. In 1993, decreases in white pine height growth, though not significant, were observed for both 2X- and 2X+CO₂-grown seedlings. Biomass and growth stimulations were observed on yellow-poplar in 1993, with mean increases of 14 percent in stem diameter and 16 percent in total plant height of yellow-poplar grown in 2X+CO₂ compared with all other treatments. Although not statistically significant at p = 0.05, 2X+CO₂-grown yellow-poplar had greater leaf, stem, branch and root biomass, and total leaf area compared with all other treatments. No significant effects on the growth of white pine were observed. However in late August 1994, both total height and basal stem diameter of 2X+CO₂-grown yellow-poplar were 21 percent greater than for all other treatments. The slower growing white pine appears to be responding differently to O₃ plus CO₂ than yellow-poplar.