Temporally disjunct herbaceous species differ in leaf embolism resistance

In the temperate Northern Hemisphere, herbaceous community composition undergoes major seasonal phenological shifts. Despite significant variation in water availability across growing seasons, few studies have associated physiological traits with seasonal shifts in community composition. Key ecophysiological traits, including leaf embolism resistance, were measured in 41 phylogenetically diverse herbaceous species native to the central forest-grassland ecotone of North America. Traits were tracked monthly in Solidago canadensis L. to explore seasonal plasticity. Correlations between ecophysiological traits and flowering time, plant height, and ecological guild were examined. Further analyses were conducted to investigate if traits were constrained by phylogeny or seasonal differences in climatic variables. Taller and later flowering species had more embolism-resistant leaf xylem and greater stomatal safety margins (SSM) than smaller, spring-flowering species. We found no seasonal variation in traits in S. canadensis, suggesting minimal seasonal phenotypic plasticity in these traits. No phylogenetic signal was found for any trait suggesting that climate rather than phylogeny drives variation in ecophysiological traits in herbs. We conclude that leaf embolism resistance and SSM are adaptively relevant traits associated with the phenological differentiation of temporally disjunct herbaceous species. The association of leaf embolism resistance and phenology has implications for herbaceous community adaptation to changing climates.