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Effects of elevated CO 2 and shade on growth and physiology in five northern tree species.
Sefcik, Lesley*,1, Ellsworth, David1, 1 University of Michigan, Ann Arbor, MI
ABSTRACT- The CO2 stimulation response of growth is variable among different tree species, and this variability is likely to have strong effects on the species composition and dynamics of successional forest communities and future landscapes. We compared four co-occurring deciduous angiosperms, Betula papyrifera, Populus tremuloides, Acer saccharum , and Fagus grandifolia , and one evergreen gymnosperm, Pinus strobus , representing groups with contrasting reported shade-tolerances. Using open-top chambers at the University of Michigan Biological Station, one-year-old seedlings were grown in two partial pressures of CO2 (ambient; 36 Pa and elevated; 56 Pa), and two levels of light (2% and 8% of full sun), reflecting the average aspen forest understory and very low light micro-sites. Physiological measurements of biomass accumulation, light response and A-Ci curves were measured to determine the effects of elevated CO2 and differing light levels on these parameters in species differing in shade tolerance. Under deep shade conditions, late successional, shade tolerant species have larger increases in relative growth rates and photosynthesis (especially in sunflecks) due to elevated CO2 compared to the less shade tolerant, early successional species. In contrast, at higher light levels, shade intolerant species have larger increases in relative growth rates and photosynthesis than the tolerant ones. The evidence suggests that under elevated CO2 conditions, shade tolerant species will have a relative carbon gain advantage over shade intolerant species, though only in deeply shaded forest environments where they currently perform better.
KEY WORDS: elevated CO 2, shade, contrasting shade tolerance, relative growth rate