Photosynthetic Light Response of Bottomland Oak Seedlings Raised under Partial Sunlight

Seedlings of cherrybark oak (Quercus pagoda Rafinesque), Nuttall oak (Quercus nuttallii Palmer) and overcup oak (Quercus lyrata Walter) were grown under two light levels, partial (20 percent) or full sunlight, to study physiological acclimation of leaves to low light availability. Shifts in leaf morphology were noted for seedlings raised beneath partial sunlight, and photosynthetic light response curves indicated that bottomland oaks varied in their degree of physiological acclimation to low light availability. Greatest shifts in leaf function under partial sunlight were observed for cherrybark oak which exhibited a 48 percent decrease in net photosynthesis at light saturation (Pn-sat), and a 55 percent decrease in dark respiration rate (Rd) (based on leaf area). These adjustments to the photosynthetic mechanism were accompanied by a 46 percent decrease in the light compensation point (LCP). In contrast, Nuttall oak leaves showed similar rates of Pn-sat, Rd and apparent quantum yield (φ) regardless of the light environment in which they developed. Overcup oak leaves were intermediate in response exhibiting a 53 percent decreased in Rd and a 57 percent increase in φ, but Pn-sat was not decreased for leaves grown under partial sunlight. Silvicultural implications of these results for bottomland oak regeneration are presented. 1Research Forester, Center for Bottomland Hardwoods Research, Southern Research Station, USDA Forest Service, Stoneville, MS. Citation for proceedings: Outcalt, Kenneth W., ed. 2002. Proceedings of the eleventh biennial southern silvicultural research conference. Gen. Tech. Rep. SRS–48. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 622 p.