Springtime Leaf Development of Mature Sessile Oak Trees as Based on Multi-Seasonal Monitoring Data

Based on a four year leaf growth data-set we modelled the thermal time-dependent leafontogeny in upper and lower canopy layers of mature sessile oak trees, in a Quercetum petraeae-cerrisforest stand (NE Hungary). Our regression models revealed no considerable differences between thetiming of leaf unfolding and leaf expansion of different canopy layers. On the other hand seasonalcourse in leaf mass-to-area ratio (LMA) indicated that sun leaves needed considerably longer thermaltime to fully develop their anatomical structures compared to shade leaves. LMA of sun leaves washigher during the whole leaf maturation process suggesting that ‘sun’ and ‘shade’ characteristicsdevelop in very early stage of leaf ontogeny. Functioning of photosynthetic apparatus (Fv/Fo) in shadeleaves have built up faster and performed better in all developmental stages which could be attributedto two main factors: 1) very early determination of leaf traits as a function of light environment and 2)evolving shading effect of upper canopy layer eliminates photoinhibition in lower leaves.