Do secondary compounds inhibit microbial- and insect-mediated leaf breakdown in a tropical rainforest stream, Costa Rica?
We examined the hypothesis that high concentrations of secondary compounds in leaf litter of some tropical riparian tree species decrease leaf breakdown by inhibiting microbial and insect colonization. We measured leaf breakdown rates, chemical changes, bacterial, fungal, and insect biomass on litterbags of eight species of common riparian trees incubated in a lowland stream in Costa Rica. The eight species spanned a wide range of litter quality due to varying concentrations of nutrients, structural and secondary compounds. Leaf breakdown rates were fast, ranging from 0.198 d(-1 )(Trema integerrima) to 0.011 d(-1) (Zygia longifolia). Processing of individual chemical constituents was also rapid: cellulose was processed threefold faster and hemicellulose was processed fourfold faster compared to similar studies in temperate streams. Leaf toughness (r = -0.86, P = 0.01) and cellulose (r = -0.78, P = 0.02) were the physicochemical parameters most strongly correlated with breakdown rate. C
