Daily carbon gain of red maple and tulip-poplar growing in ambient and elevated CO2 in a forest understory environment.
NAUMBURG, E.* 1, D.S.ELLSWORTH 1,2 and R.W.PEARCY 1
Duke University, Durham, NC 27708-3028 USA 1
Brookhaven National Laboratory, Upton, NY 11973-5000 USA 2
It has long been of interest to determine whether carbon gain differences in species underlie observed species differences in apparent shade tolerance. Further, increasing atmospheric CO2 could differentially affect carbon gain in species with contrasting shade tolerance. We estimated daily carbon gain under ambient and elevated CO2 in red maple (Acer rubrum, shade tolerant) and tulip-poplar (Liriodendron tulipifera, shade intolerant) with a physiological and architectural model and allometric relationships for saplings in Duke Forest, NC. Daily courses of PFD (photosynthetic photon flux density) were estimated using canopy photos together with a ray-tracing model (YPLANT) that contained spatial information for branches of 22 of study plants. These PFD courses were used in a dynamic sunfleck photosynthesis model that predicts photosynthesis as a function of light and species-specific photosynthetic parameters. Daily photosynthesis of whole plants was scaled from individual branches using leaf-area-stem diameter relationships. At ambient CO2, tulip-poplar had slightly higher canopy daily carbon gain than red maple because of slightly higher leaf-level carbon assimilation and higher leaf area in plants < 2 cm diameter (0.5 m height). At larger diameters, however, red maple had higher canopy-level carbon gain because of higher leaf areas. Under elevated CO2 in FACE, red maple had similar canopy assimilation rates as tulip-poplar despite greater photosynthetic enhancement in red maple under elevated CO2. The latter was due to slight reductions in specific leaf area that resulted in lower canopy leaf area for red maple under elevated CO2. These results indicate that while shade intolerant species can have a carbon gain advantage when small, this advantage is not maintained for larger saplings and may contribute to low understory survival. Elevated CO2 will not change this pattern.
Keywords: shade tolerance, elevated CO2, carbon gain, sunflecks
This abstract is being presented at: 10:30 AM in session:
Poster Session #18: Elevated CO2.