Large trees experience strong microclimatic gradients within their crowns, particularly in irradiance, which decreases exponentially from the top canopy downwards. Light availability affects the morphology, photosynthesis, and construction cost of leaves and branches, but to date it remains unclear whether these effects translate to a different carbon balance of sun and shade branches. In our new study, current and former PPE members Cedric Zahnd, Miro Zehnder, Ansgar Kahmen and Günter Hoch used data collected from mature trees at the Swiss Canopy Crane II site to compare relative carbon costs (i.e. branch carbon cost expressed as percentage of life-time carbon uptake) between sun and shade branches. We found surprisingly similar relative carbon costs between sun and shade branches and among the nine studied species. Our results highlight that, at least in forests with relatively open canopies, the balance of assimilation and carbon costs at the branch-level is finely tuned along the light gradient, suggesting a high degree of C autonomy even in shaded branches.

 Link to the publication: https://onlinelibrary.wiley.com/doi/full/10.1111/pce.70413