Intra‐crown variation of leaf mass per area of Fagus crenata is driven by light acclimation of leaf thickness and hydraulic acclimation of leaf density.

In trees, leaf anatomy acclimates to the vertical light and hydraulic gradients within the crown. Intra‐crown trait variation reflects phenotypic plasticity, which is considered a measure of individual‐level acclimation to environmental variation. Here, we compared plasticity of leaf anatomical traits among trees from five regional populations of Fagus crenata and assessed the contribution of these traits to leaf mass per area (LMA). Intra‐crown variation of LMA was larger than variation among trees from different sites, suggesting phenotypic plasticity is greater than genetic variation. After intra‐crown light effects were removed, LMA increased with increasing height, suggesting, in addition to light acclimation, hydraulic limitation drives intra‐crown variation. LMA was positively correlated with leaf thickness and negatively correlated with mesophyll porosity. Leaf thickness accounted for 39% of the variation in LMA, while palisade thickness accounted for 62% of the variation in leaf thickness, suggesting light was the main driver of leaf thickness. Thicker leaves also had denser mesophyll and thicker epidermal layers, both acclimations to low water availability (i.e., hydraulic limitation). Among the traits, intra‐crown plasticity was highest for mesophyll porosity, while there was no difference among trees from different sites in overall trait plasticity. Our results indicate phenotypic plasticity of leaf traits in F. crenata is mainly driven by light availability, while some traits, such as leaf density, may be driven by hydraulic limitation. In regional populations with high phenotypic plasticity, individual‐level acclimation may buffer negative effects of future climate change on growth and productivity of F. crenata. [ABSTRACT FROM AUTHOR]