Relationship between herbivory and leaf traits in mangroves on Iriomote Island, southern Japan

Leaf herbivory potentially affects carbon (C) and nutrient cycling in forest ecosystems. It is especially critical to study the leaf herbivory rates in mangroves to understand the pattern of resource changes from the detrital pathway to the grazing pathway. However, determinants of leaf herbivory rates in mangroves are poorly understood. We examined the differences in leaf herbivory rates among leaf phenotypes (sun or shade leaves), leaf ages (young or old leaves), and season (summer or winter) and investigated the relationships between the leaf herbivory rates and 12 leaf traits (including chemical, physiological, and physical/mechanical traits) in each of six communities from the seaward fringe to the inland of subtropical mangroves on Iriomote Island, southern Japan. The herbivory rates decreased from seaward to landward mangrove species, excluding one species in the landward mangroves. The herbivory rates also decreased as the concentration of condensed tannins or the tannins:nitrogen ratio increased but did not correlate with the other leaf traits. Overall, season, leaf phenotype, and leaf age had no effect on the herbivory rate. However, in the two seaward and one rhizophoraceous species, the herbivory rates were higher in summer than in winter and were affected by the leaf phenotypes. The concentration of leaf condensed tannins moderately influenced leaf herbivory, fluctuating from seaward to landward; therefore, it was one of the factors driving the grazing pathway in mangroves. Understanding these mechanisms is critical for a comprehensive appreciation of the high productivity of and nutrient cycling in mangrove forest ecosystems.