Leaf Trait Variation in Eurya emarginata Across Four Island Populations and Under Experimental Shading

Whether the leaf economics spectrum (LES) and its trait correlations operate at the intraspecific level, and how light versus soil nutrients are associated with leaf traits, remain unclear in stress-tolerant island plants. We quantified leaf morphological, anatomical, and LES traits of Eurya emarginata across four island populations and evaluated their associations with field-measured light availability (canopy density) and soil conditions; a shading experiment was used to test light-driven plasticity directly. Across field populations, leaf anatomical traits showed greater variability than LES traits (Kruskal–Wallis, p = 0.001). Most leaf trait pairs were correlated at the metapopulation level, whereas within local island populations many of these correlations became non-significant; this pattern may reflect smaller sample sizes and narrower trait ranges within islands as well as possible biological decoupling. Redundancy analysis indicated that canopy density was the main variable associated with leaf morphological and anatomical trait variation, whereas soil nutrients were the main variables associated with LES trait variation. The shading experiment confirmed that reduced light availability altered structural and photosynthetic traits. Our results show that light and soil conditions are associated with different trait groups, and that trait associations are scale-dependent. We conclude that intraspecific leaf trait variation in island populations is context-dependent, with anatomical traits varying more than LES traits, and that trait correlations observed at broad scales are not necessarily maintained within local populations.