From intraspecific plasticity to community-level trait filtering: shifts toward mechanically robust and resource-conservative traits near the shoreline of a coastal dune

Abstract Coastal dunes exhibit spatially heterogeneous environmental gradients, yet plant functional trait responses to such gradients at both within-species and community levels remain unclear. Here, we examined intraspecific and interspecific variation in leaf and root traits along a shoreline–inland gradient encompassing foredunes, interdunes, and backdunes at the Tottori Sand Dunes, Japan, by quantifying intraspecific variation for two dominant species ( Carex kobomugi and Ischaemum anthephoroides ) and assessing interspecific variation using community-weighted mean (CWM) trait values. In C. kobomugi , most leaf traits changed monotonically along the shoreline–inland gradient, with leaf toughness as a significant exception exhibiting a unimodal pattern. Shoreline individuals exhibited thicker, tougher leaves, whereas inland individuals expressed higher specific leaf area, indicating strong phenotypic plasticity across contrasting stress regimes. In contrast, I. anthephoroides exhibited intraspecific responses concentrated mainly on increased leaf height, indicating that the magnitude and dimensionality of intraspecific trait plasticity are species-specific. At the community level, CWMs exhibited more pronounced directional shifts, with resource-conservative, mechanically robust traits increasingly dominant along the coast. Root traits showed little intraspecific variation; however, CWM of root dry matter content increased inland, indicating community-level filtering toward conservative root strategies in inland communities. Together, results show increasing shoreward coastal stress favors mechanically robust and resource-conservative traits, expressed through species-specific plasticity in dominant species and community‐level trait filtering associated with observed compositional shifts along the shoreline–inland gradient.