Effects of light intensity on the growth and energy balance of photosystem II electron transport in Quercus alba seedlings

Abstract

Quercus alba (white oak) seedlings were grown at four levels of irradiance (5, 15, 30 and 100% of full sunlight) under a rain out shelter. After one growing season, the greatest diameter and height growth, biomass (root, leaf, and stem) and leaf area were observed on seedlings under 100% of full sunlight. Seedlings under 15, 30 and 100% of full sunlight allocated more biomass to roots (∼ 70%) than seedlings under 5% of full sunlight (∼ 58%), suggesting a priority in root growth unless light is severely limited. Leaf weight ratio, specific leaf area, and leaf area ratio increased with the degree of shading, indicating acclimation of leaves to different light intensities. Acclimation to light intensity closely correlated with the fluorescence parameter 1-qP. Non-photochemical quenching was also affected as shade intensity increased. The apparent reduction in electron transport rate (ETR) through photosystem II (PS II) increased with light intensity, and light saturated ETR under 5% of full sunlight was only 46% of that under full sunlight. The shift from photochemical to non-photochemical quenching occurred in response to increasing actinic light and as growth irradiance declined, the 'quenching shift rate' declined as well. Overall, Quercus alba seedlings demonstrated strong growth and allometric responses to light intensity. © INRA, EDP Sciences, 2006.