Abstract
Because of the importance of hydraulic architecture in understanding physiological differences between small and large trees, we tested the hypothesis that foliar δ13C increased with aboveground flow-path length in longleaf pine (Pinus palustris Mill.) trees of varying age and size at two sites in the lower Coastal Plain. This species offered a unique opportunity to examine variability in foliar δ13C in relation to pathway length because of the open, well-mixed canopy in savanna-like stands and concentration of foliage in splayed tufts on branch ends. At both sites, models with total flow-path length (bole + branch) explained 78–81% of the variation in foliar δ13C, and a full model with separate slopes and intercepts for each tree was required. Branch flow-path length was highly correlated with foliar δ13C and the models accounted for 76–88% of the variation in foliar δ13C, and a reduced model with one slope was suitable for each site. Flow-path length was not as well correlated to foliar N concentration, specific leaf area or tuft leaf area. Greater δ13C enrichment with increasing flow-path length indicates the need for mechanistic studies to better understand the role of hydraulic resistance in controlling leaf-level physiology within the canopy and among different size longleaf pine trees.