Intracanopy variation in leaf morphology and physiology in dominant shrubs of Florida’s xeric uplands

Abstract

The variation in morphological traits and photosynthetic potentials associated with light conditions in the canopy can determine whole-plant function. However, leaf structure–function relationships are poorly studied in ecosystems experiencing nominal light attenuation. We examined morphological leaf traits (area, specific leaf area, thickness, revoluteness, length–width) and photosynthetic traits estimated from rapid light curves (PARsat, ETRmax, light harvesting efficiency α) in seven shrub species in two xeric upland ecosystems of Florida: rosemary scrub and sandhill. Across species and ecosystem types, shade leaves had greater specific leaf area, were thinner, and less revolute than sun leaves. Surprisingly, shade leaves had smaller areas than sun leaves. Three out of six species showed a tight relationship between morphological and photosynthetic traits. Species common to both sandhill and rosemary scrub ecosystems showed similar photosynthetic traits but greater sclerophylly in the scrub ecosystem. Overall, greater leaf thickness and greater leaf area of upper canopy leaves yielded higher photosynthetic capacities and saturation at higher photon flux densities compared with lower canopy leaves. Our results suggest that variation in leaf morphological traits governed by patterns in light availability have functional significance; however, ecosystem properties such as nutrient availability might also impact light-driven structure-function relationships.