Effects of exotic fruit plants on leaf decomposition in Amazon: a study in aquatic microcosm

Introduction of exotic species into riparian vegetation can result in a negative impact on invertebrates and microorganisms and, consequently, on leaf litter decomposition. In Manaus (Brazil), exotic fruit plant species are commonly planted in the riparian zones of streams. We assessed the effects on leaf litter decomposition of replacing native vegetation ( Goupia glabra , Mabea speciosa and Protium spruceanum ) by exotic species ( Artocarpus heterophyllus , Carica papaya , Mangifera indica , Musa paradisiaca and Syzygium malaccense ) in Amazonian aquatic environments. We performed one-choice feeding (OCF) and multiple-choice feeding (MCF) experiments to evaluate leaf consumption, survival of shredders (Trichoptera: Phylloicus elektoros ), fungal sporulation rate, and microbial decomposition. Richness of aquatic hyphomycete spores was similar in all species. Sporulation rate was higher in the exotic plant S. malaccense . We recorded shredder death only in the OCF experiment with exotic species with tough leaves. Microbial decomposition was higher in exotic plants A. heterophyllus and M. indica in the OCF and MCF experiments, respectively. Leaf consumption by shredders was higher in the native plant M. speciosa in the OCF experiment and in the exotic plant C. papaya in the MCF experiment. We concluded that the effects of introducing exotic plant species into a riparian zone on shredder survival and leaf litter decomposition appear dependent on the characteristics of the leaves introduced and the species present in the riparian forest.