Low light acclimation in five temperate broad-leaved tree species of different successional status: the significance of a shade canopy

Tree species differ largely in their capability to produce characteristic shade leaves with effective morphological and physiological acclimation to low light. By examining the sun/shade leaf differentiation in leaf morphology, foliar nitrogen and photosynthetic capacity in five temperate tree species of different successional status, we aimed at identifying those leaf traits that determine the development of a typical shade crown with low light-acclimated leaves. Leaf morphology, foliar N content, photosynthetic capacity (V (cmax), J (max) and A (max)) and leaf dark respiration (R (d)) were measured in the canopies of 26 adult trees of Fraxinus, Acer, Carpinus, Tilia and Fagus species. Six traits (the sun/shade leaf differentiation in specific leaf area, leaf size, A (max) per leaf area or per mass, photosynthetic N use efficiency and R (d)) were found to characterise best the degree of low light acclimation in shade leaves. All five species exhibited certain modifications in leaf morphology and/or physiology in response to low light; Fagus sylvatica showed the highest and Fraxinus excelsior the lowest shade leaf acclimation. Our results indicate that the five early/mid- to late-successional species have developed species-specific low light acclimation strategies in their shade crowns which differ in terms of the relative importance of leaf morphological and physiological acclimation.