Variability of stomatal conductance, leaf anatomy, and seasonal leaf wettability of young and adult European beech leaves along a vertical canopy gradient

Abstract

This study assessed the variation of leaf anatomy, chlorophyll content index (CCI), maximal stomatal conductance (gsmax) and leaf wettability within the canopy of an adult European beech tree (Fagus sylvatica L.) and for beech saplings placed along the vertical gradient in the canopy. At the top canopy level (CL28m) of the adult beech, CCI and leaf anatomy reflected higher light stress, while gsmax increased with height, reflecting the importance of gas exchange in the upper canopy layer. Leaf wettability, measured as drop contact angle, decreased from 85.5° ± 1.6° (summer) to 57.5° ± 2.8° (autumn) at CL28m of the adult tree. At CL22m, adult beech leaves seemed to be better optimized for photosynthesis than the CL28m leaves because of a large leaf thickness with less protective and impregnated substances, and a higher CCI. The beech saplings, in contrast, did not adapt their stomatal characteristics and leaf anatomy according to the same strategy as the adult beech leaves. Consequently, care is needed when scaling up experimental results from seedlings to adult trees.