Direct and Element‐Mediated Edaphic Effects Shape Resource‐Conservative Leaf Trait Variation Across Serpentine and Limestone Soils

Edaphically extreme substrates, such as serpentine and limestone, impose strong physiological constraints on plants and are frequently associated with resource-conservative leaf traits and narrow plant endemism. However, it remains unclear how edaphic selection shapes leaf traits and whether these shifts are driven primarily by direct soil-imposed constraints or indirectly by changes in leaf elemental composition. Here, we examined soil–leaf elemental relationships, leaf functional traits, and CSR strategies (Competitive, Stress-tolerant, and Ruderal strategy) using piecewise structural equation modeling across 16 populations of five closely related Epimedium taxa distributed on serpentine, limestone, and other substrates in western Japan. Despite marked differences in soil and leaf elemental composition between serpentine and limestone sites, populations on both substrates converged toward resource-conservative leaf traits, including lower specific leaf area (SLA) and a shift toward thicker leaves and higher leaf dry matter content (LDMC), even after accounting for species identity. Piecewise structural equation modeling revealed two pathways consistent with the proposed hypotheses: A strong direct association between soil elemental composition and leaf trait variation and a weaker indirect association involving leaf elemental composition. Together, our results suggest that edaphic mosaics are linked to convergent resource-conservative phenotypes through two partly overlapping pathways across serpentine and limestone soils: strong direct associations with leaf functional traits and weaker associations involving leaf elemental composition.