Light acclimation and photosynthetic response of beech (Fagus sylvatica L.) saplings under artificial shading or natural Mediterranean conditions

Acclimation of beech (Fagus sylvatica L.) to different light conditions was studied in natural regeneration below black pine canopies (Pinus nigra ssp. nigricans) in Mont-Ventoux (Vaucluse, France) and with potted saplings-from the same origin-under shaded tunnels in southern France (Avignon, Vaucluse), and north-eastern France (Nancy, Meurthe-et-Moselle). Leaf mass to area ratio and leaf carbon content per unit mass increased, while leaf nitrogen content per unit mass (N-m) remained constant, with increasing relative irradiance (RI). Maximum carboxylation rate (V-cmax) and maximum electron transport flux (J(max)) increased with RI and were higher in the natural regeneration than in the potted saplings. These two parameters were higher for the potted saplings in north-eastern France than for those in southern France. Leaf nitrogen allocation to carboxylation (P-r) or bioenergetics (P-b) did not vary with RI. P-r and P-b were higher in the natural regeneration than in the potted saplings, whereas N-m was lower in the natural regeneration than in the fertilised potted saplings. Seasonal time course of these parameters in the natural regeneration in Mont-Ventoux, from bud burst to the beginning of summer drought, showed that after the leaf expansion period, leaf composition and photosynthetic parameters remain globally constant.