Vertical variation and economic strategy of leaf trait of major tree species in a typical mixed broadleaved-Korean pine forest

Aims An analysis of the variations in leaf traits of different tree species contributes to the understanding of plant community structures.Methods This study explored the effect of the light environment on leaf traits at different canopy heights in a typical mixed broadleaved-Korean pine forest. We measured the leaf mass per area (LMA), leaf thickness (LT), leaf dry matter content (LDMC), chlorophyll content (CCI), leaf carbon content (C), mass-based and area-based nitrogen content (N_mass and N_area), and mass-based and area-based phosphorus content (P_mass and P_area) for 15 broad-leaved tree species in this forest.Important findings We found that the LMA of Fraxinus mandschurica and Populus ussuriensis in the upper canopy were significantly higher than that in the lower canopy, but no significant vertical changes were detected in other species within the canopy. The CCI of Betula platyphylla increased from the lower to upper canopy. In contrast, the CCI of Ulmus japonica in the upper canopy was significantly higher than that in the middle canopy. The N_mass of Fraxinus mandschurica in the middle canopy was significantly higher than that in the upper canopy. These results indicated that the variations in leaf traits within the canopy were different among species. The LMA was positively correlated with the LT and LDMC in all three canopies, but the correlations of other trait combinations were only significant in one or two canopies. The results suggest that the leaves of Populus davidiana and Populus ussuriensis tend to adopt survival strategies involving lower photosynthetic ability, nutrient concentrations, and respiratory rates, while the leaves of Phellodendron amurense and Maackia amurensis tend to be located at the other end of the economics spectrum with contrasting trait values. Differences in species response to light may alter leaf morphological and chemical traits in canopy layers, and hence contribute to community assembly and species coexistence.