Differences in leaf and root tip traits between tree species growing on ridges and in valley of a subtropical evergreen broad-leaved forest in southwestern Japan

Abstract

The leaf and root tip traits of tree species have evolved to acquire resources, such as light, water, and nutrients, in their habitats. Understanding the relationships between leaf and root tip traits and growth environments provides critical insights to predict tree community responses to environmental change. The aim of this study was to elucidate the differences in leaf and root tip traits among tree species and their relationships with topographic differences in subtropical trees. We measured four leaf traits (specific leaf area, thickness, area, and nitrogen concentration) and four root tip traits (specific root tip length, tissue density, diameter, and nitrogen concentration) and analyzed the difference in leaf and root tip traits between tree species specifically growing on ridges (ridge species) and in valleys (valley species) and the relationships among the traits. Leaf traits differed between ridge and valley species, whereas root tip traits did not differ. Ridge species formed small, thick, low-nitrogen leaves, which are possibly associated with high dry and wind stress tolerance, whereas the valley species formed broad, thin, high-nitrogen leaves, which may be associated with high light-acquisition efficiency. These patterns reflect a trade-off between resource acquisition and stress tolerance for leaf traits. Furthermore, the relationships between leaf and root tip traits were confirmed only for the nitrogen concentration: the leaf nitrogen concentration was positively correlated with the root tip nitrogen concentration. This result implies that tree species optimally balance photosynthetic activity with nutrient- and water-absorption activities by varying nitrogen concentrations.