The Influence of Litter Diversity on Leaf Breakdown and the Colonization of Decomposer Communities in Subtropical Highland Grassland Streams

Abstract

Litter diversity can enhance leaf breakdown through selective effects when driven by a particular species or specific leaf chemical characteristics. We analyzed the influence of leaf mixtures on leaf breakdown and associated decomposers in a highland grassland stream that receives low-diversity leaf inputs. We incubated leaves of Ocotea diospyrifolia, Nectandra megapotamica, Myrcia eugenioides, and Miconia flammea in coarse mesh litter bags containing a leaf mixture of the four species, as well as leaves of each species in single treatments (6 streams × 3 replicates × 5 treatments = 90 sampling units). We found that leaves in single treatments had higher breakdown rates than the mixed treatment, suggesting that increased litter diversity did not positively influence leaf breakdown in highland grassland streams. Adaptations of decomposer assemblages to poorly structured riparian vegetation may have outweighed the potential effects of litter diversity. We found higher importance of leaf quality, measured by nutrient content, in driving leaf breakdown, with the effect of litter diversity on leaf breakdown rates depending on individual leaf chemical characteristics. Despite the lack of litter diversity positive effects on breakdown rates, the mixture treatment showed higher diversity of fungi and invertebrate decomposers. The leaf mixture may have increased habitat structure but reduced the number of individuals due to increased resource heterogeneity, favoring specialists. Functional feeding groups exhibited the expected patterns for their feeding strategies, with shredders benefiting from litter diversity and scrapers preferring single leaf treatments. Overall, riparian vegetation diversity was not crucial for organic matter processing but positively influenced decomposer diversity.