Litter decomposition of exotic and native plant species of agricultural importance in Amazonian streams

The conversion of riparian vegetation into monocultures alters the input of allochthonous energy and the heterotrophy of streams. Here, we aimed to assess the implication of leaf litter inputs from plant species of agricultural importance on decomposition in Amazonian streams. We hypothesized that decomposition is low in litter with high concentrations of lignin and cellulose, regardless of the origin of plant species (exotic or native). We incubated leaf litter from plant species of agricultural importance, such as cocoa (native) and oil palm (exotic), as a control, leaf litter of Hymenaea courbaril (native) in four streams for 60 days. Contrary to our initial expectations, the leaf litter from oil palm, which was of higher quality and had lower concentrations of structuring compounds (lignin and cellulose), did not differ in decomposition rates from the lower quality leaf litter of the control species, which presented higher concentrations of structuring compounds. We recorded higher decomposition rate in cocoa, which had intermediate concentrations of structural compounds. Our results indicate a negative effect of the conversion of riparian vegetation into oil palm monocultures (Elaeis guineensis) for the processing of organic matter in Amazonian streams, due to the slower decomposition rate of the leaf litter of this species.