PARENT SESSION
Oral Session # 64: Plant Ecology V: Physiology and Function II.
Presiding: G North
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 102.

Does elevated CO₂ alter growth allometry of northern tree species?

Kubiske, Mark^*,1, McDonald, Evan¹, Marquardt, Paula¹, King, John², Zak, Don³, Pregitzer, Kurt², Holmes, Bill³, Karnosky, David², ¹ US Forest Service, Rhinelander, WI² Michigan Technological University, Houghton, MI³ University of Michigan, Ann Arbor, MI

ABSTRACT- In two separate experiments, various planting arrangements of aspen (Populus tremuloides), birch (Betula papyrifera) and maple (Acer saccharum) trees were grown in elevated CO₂ in factorial combination with soil fertility (using open-topped chambers), and atmospheric ozone (using the Aspen FACE facility). Trees were harvested after at least three growing seasons under treatments, and dissected into dry mass of leaves, wood, coarse roots and fine roots (<2 mm diam). In both experiments, elevated CO₂ significantly increased total tree and organ biomass. The CO₂ effect on growth was augmented by high N soil and eliminated by elevated O₃. There were few significant effects of CO₂, soil N, or O₃ on biomass allocation among different plant organs. Regression analysis indicated that such effects were driven by differences in tree size and were not true shifts in growth allometry due to CO₂, soil N or O₃. In open-topped chambers, aspen in monoculture were significantly smaller than aspen grown in combination with maple, whereas the reverse was true for maple. In FACE, aspen trees in monoculture were significantly larger than those grown with maple. In both experiments, aspen trees grown in monoculture had a larger proportion of biomass in stems and a smaller proportion of biomass in roots compared to those grown in combination with maple. In open-topped chambers, maple grown in combination with aspen had larger proportion of biomass in leaves whereas those in monoculture had larger proportion in roots. Regressions indicated that differences in biomass allocation among planting arrangements represented real shifts in growth allometry. Results from both experiments indicate that elevated CO₂, elevated O₃, and soil N availability have minimal effect on growth allometry whereas competitive interactions with other species are very influential in altering growth allometry.

Key words: FACE, soil N, competiton, ozone