Abstract: Leaf functional traits reflect the ecological strategies of plants and influence their growth and distribution. While variation in leaf traits has been extensively documented across species in terrestrial ecosystems, studies in wetland ecosystems can enhance the understanding of leaf trait variation along environmental gradients. Intraspecific studies are particularly valuable for exploring trait variation and its underlying mechanism. Coastal wetlands have become hotspots for studying trait variation, and the invasive Spartina alterniflora, distributed along China’s coastline, is an ideal species for investigating leaf traits variation. We examined the geographical variation and abiotic drivers of six leaf functional traits and explored the roles of phenotypic plasticity and genetic differentiation through a two-year common garden experiment. We also analyzed the relationships between leaf traits and growth performance in both field and common garden. All leaf traits exhibited significant geographical variation, which were affected by both climatic and sedimentary variables. Common garden experiment exhibited trait-dependent response, with different leaf traits showing varying degrees of plastic response or genetic differentiation. Variation in leaf size, leaf thickness and specific leaf area was primarily driven by genetic differentiation, while variation in leaf density and leaf dry matter content was largely due to phenotypic plasticity. Leaf size and thickness were positively correlated with growth performance in both field and common garden. This study advances the understanding of leaf trait variation in terrestrial ecosystems and highlights how multiple abiotic variables shape latitudinal patterns in leaf traits. The resource acquisition strategy at high latitudes in the northern hemisphere contributes to the strong growth performance of S. alterniflora, potentially facilitating its northward expansion. In contrast, the resource conservation strategy at low latitudes may hinder its southward expansion.

Key words: adaptive mechanism, common garden, growth, latitudinal gradient, leaf traits, Spartina alternifora