Do chestnut, northern red, and white oak germinant seedlings respond similarly to light treatments? II. Gas exchange and chlorophyll responses

Abstract

Understanding differences in physiological and growth strategies in low-light environments among upland oak species may help managers address the challenges of oaks’ poor regeneration. Gas exchange and chlorophyll content were measured for northern red oak ( Quercus rubra L.), chestnut oak ( Quercus prinus L.), and white oak ( Quercus alba L.) germinants grown at 25%, 18%, and 6% of full sun in one of two native forest soil mixes for two summers. Northern red and chestnut oak photosynthesis at saturating light (Amax, mass) increased by 23%–36% as light levels increased from 6% to 25% of full sun, while white oak Amax, massdeclined by 20% and plateaued at 18% of full sun. White oak light compensation point is representative of deep shade (7.2 µmol·m–2·s–1), while northern red and chestnut oak averaged 17.8 µmol·m–2·s–1. Total chlorophyll content increased as light levels decreased for all species. Of the three species, the slow-growing white oak seedlings appeared to be more efficient in utilizing light than northern red or chestnut oak seedlings. This suggests no additional benefits to increasing light above that typically found in a light shelterwood cut; however, it is crucial to control faster-growing competing vegetation.