Leaf palatability is driven by trait variation within Quercus robur crowns

Anjaharinony Andry Ny Aina Rakotomalala , Tobias Müller, Susanne Walden, Annabell Rosemarie Wagner, Lucy Saueressig, Anke Becker, Maaike Bader, Robert R Junker, Christian Lampei, Esther Meissner, Lars Opgenoorth, Stefan Pinkert, Nina Farwig

Plant–herbivore interactions vary across spatial and temporal scales in response to environmental gradients. However, despite substantial variation in leaf traits even within individuals and under similar environmental conditions, the role of leaf traits in shaping leaf palatability remains poorly understood. Here, we disentangled the effects of leaf trait variation from those of crown strata (sun vs. shade) and season on leaf palatability within the crowns of Quercus robur forest trees. Palatability was measured in no-choice feeding bioassays with Lymantria dispar caterpillars as consumed leaf volume per unit caterpillar mass. We related palatability to structural traits, including leaf dry matter content (LDMC) and leaf mass per area (LMA), and proxies for chemical traits including flavonol, anthocyanin, and nitrogen balance index (NBI). We found that more palatable leaves had higher NBI but lower LDMC, LMA, and flavonol content. Shade leaves were generally more palatable than sun leaves, reflecting trait differences between crown strata. Leaf palatability fluctuated among seasons and didn’t strictly mirror seasonal shifts in leaf traits. Our findings highlight that leaf palatability arises from spatially structured variation in leaf traits within tree crowns, whereas temporal palatability variation is highly complex and driven by factors beyond structural and chemical leaf traits.