Differences in foliar water uptake rate between sun and shade leaves of beech

Foliar water uptake (FWU) is a hot topic among the scientific community. With an increase in projected droughts, FWU can provide a means for plants to maintain a water status sufficient to continue physiological processes. The capability of plants for FWU is well-recognized across numerous species, prompting studies that typically emphasize interspecific comparisons to underscore this mechanism’s importance. While this approach is of utmost importance to elucidate on the fitness and competitive strength of species in the face of climate change, water absorption through leaves is not uniform. It varies even within individual trees. This variation is especially evident in trees that show vertical leaf differentiation due to varying microclimatic conditions within their canopies. This study focused on beech (Fagus sylvatica L.) trees, comparing FWU rates between sun-exposed and shaded leaves of an adult tree specimen. The observed discrepancy in uptake rates (Q) between sun and shade leaves hints toward different FWU dynamics. These results are a first step in disentangling the generalizations about leaf water absorption. Studying FWU at a higher spatial resolution at the leaf level within a species, may therefore allow for more nuanced conclusions regarding its importance for particular species.