Growth, morphology, and biomass allocation of recently planted seedlings of seven European tree species along a light gradient

Light is one of the most critical factors controlling tree survival and growth. Limited light availability induces phenotypic plasticity, thus enabling plants to adapt to suboptimal conditions. The plastic responses are species-specific and are thought to largely depend on species' shade tolerance. This study aims to add to existing research by trying to disentangle the effects of light, species identity, and shade tolerance on growth, biomass partitioning, and morphology of seedlings of seven common European tree species. For that purpose, we set up a shading experiment where seedlings were grown under three levels of light availability (15%, 35%, and 100%). A destructive harvest was carried out for the assessment of biomass allocation and structural complexity of plant architecture after a year of exposure to limited light. The specific leaf area increased with decreasing light availability for all species. However, we found little to no changes in relative height and diameter growth, biomass allocation to aboveground tree compartments, and structural complexity along the light gradient. We argue that because trees were grown under open field conditions, both in the nursery and for the first year of the experiment, it might have resulted in a delayed response to limited light availability. Assuming the delayed reaction of less plastic plant organs, we expect that the morphological adaptations of the tree species and intra- and interspecific differences will become more pronounced, as the trees grow older.