Associations among leaf traits should change as plants grow due to shifts in resource requirements and availability, but it remains unclear how these associations change across ontogenetic stages, especially in species-rich forest communities. For over 50 co-occurring woody species in a Japanese temperate forest, we measured leaf traits (LMA: leaf mass per area, leaf size, leaf thickness, leaf strength, DMC: dry matter content, C: carbon, N: nitrogen, P: phosphorus, and secondary metabolites) at four ontogenetic stages of current-year seedling, seedling, sapling, and adult. We evaluated leaf trait associations, and also their relationships with seed mass, separately at each ontogenetic stage, using principal component analysis.
We found that, in current-year seedlings, most leaf traits (e.g., leaf size, LMA, strength, DMC, and lignin) and seed mass, except foliar nutrient contents (N and P), were positively associated with the PC1. On the other hand, at later ontogenetic stages, the PC1s were associated with fewer leaf traits, showing the trade-off between LMA and N commonly known as leaf economics spectrum. These results suggest that seed mass has strong influences on leaf morphological and physical traits of current-year seedling, although leaf trait associations gradually diverged as plants grow being independent of seed mass.