Functional coordination among leaf, xylem, phloem and ray parenchyma governs the carbon-water economy of woody plants, yet the allocation principles and climatic drivers remain poorly explored. We hypothesized that species at lower altitudes and/or latitudes invest more in xylem and phloem per unit leaf area to compensate for higher transpirational losses, whereas species from higher altitudes and/or latitudes allocate proportionally more to ray parenchyma to enhance storage. Using canopy cranes across four Chinese forests, we quantified how leaf area, branch tissue cross-sectional areas, constituent cell types and functional traits for 55 canopy species varied and coordinated along altitudinal and latitudinal gradients. Contrary to the hypothesis that warmer climates favour greater xylem and phloem investment per leaf area, we found lower xylem-to-leaf and phloem-to-leaf ratios at low altitudes/latitudes, while ray-parenchyma-to-leaf ratios increased with altitude. Our findings demonstrate that functional ratios diverge across climates but converge within similar environments, suggesting environmental filtering drives storage-transport balances. In contrast to our expectation, trees in cold climates prioritize ray-parenchyma storage or hydraulic capacity, likely due to short growing seasons and freeze-thaw embolism repair needs. Our results imply that coordinated tissue allocation acts as an important adaptive for balancing transport and storage across diverse environments.
Zhang et al. (Tue,) studied this question.