Plant Litter from Rare Species Increases Functional Diversity and Decomposition of Species Mixtures

Biodiversity loss is altering key ecosystem processes as primary production and decomposition, however, the after-life effects of plant diversity (species-mixing effects) on instream organic matter (litter) decomposition is still under debate. Available evidence of litter species-mixing effect (or the lack of) comes from studies using dominant plant species, despite rare species comprising the majority of species in an ecosystem and can contribute to ecosystem functions or in the provisioning of essential elements. Here, we simulated different extinction scenarios of plant from rare species by incubating leaf litter in artificial channels located within a tropical stream. We thus, assessed whether the loss of litter from rare plant species alters functional diversity (resource dissimilarity) and litter quality (resource concentration) of species mixtures and change decomposition, N loss and fungal biomass production. We show that the loss of litter from rare plant species reduced the functional diversity of litter mixtures and consequently, reduced decomposition, N loss and fungal biomass production. Although species lost also changed the nutritional quality of litter mixtures (resource concentration), it did not affect decomposition or N loss but fungal biomass production. Also, when only similar rare species were present, processes were reduced to higher rates than in the scenario with only dissimilar rare species (except for N loss). Our findings reveal the relevance of litter from rare plant species to key ecosystem processes related to carbon and nutrient flow in tropical streams, especially when dissimilar traits are added to litter pools.