Daily carbon assimilation and sunflect utilization in a northern hardwood understory.

Abstract

Daily light levels were measured for a cloud free day in midsummer in three northern hardwood stands. Maximum gross photosynthetic rates, estimated daily carbon assimilation, and the percentage of assimilation due to sunflecks were determined for three species of understory seedlings (Fagus grandifolia, Acer saccharum, and Fraxinus americana). F. americana, a less shade tolerant species, had the highest maximum gross photosynthetic rates. F. grandifolia, a very tolerant species, had the lowest estimated carbon assimilation. Plants with the highest estimated carbon assimilation were growing in the stand with the highest daily light levels. Temepratures at which gas exchange measurements were taken signficantly affected maximum photosynthetic rates. Microsite variation in light levels were found to have a strong effect on the percentage of a plant's carbon gain due to sunflecks.