Numerous studies have emphasized the role of riparian forests as buffers against the effects of land use on streams. However, the value of isolated forest remnants in deforested areas remains unclear. Herein, we explored the potential of forest fragments to minimize the impacts of riparian deforestation on leaf breakdown rates mediated by microorganisms and detritivores. We conducted leaf breakdown experiments in eight streams within agricultural catchments (SE, Brazil): four running from forest to deforested reaches and four running from deforested to forest reaches. We used four replicates of each stream reach type: "forest upstream", "forest downstream", "deforested downstream", and "deforested upstream". In each reach, we incubated leaves of the native tree species Miconia chartacea (a fast-decomposing species) and Inga laurina (a slow-decomposing species) in single and mixed treatments, using fine and coarse mesh bags. Leaf breakdown rates depended on the presence of invertebrates and stream reach types. However, the interaction of these factors did not affect leaf breakdown rates of I. laurina in both single and mixed treatments. Invertebrates contributed to the breakdown of M. chartacea leaves in single and mixed treatments, but this contribution depended on the reach type. Specifically, leaf breakdown was lower in deforested upstream reaches than in forest upstream. The effect of the interaction between invertebrates' presence and stream reach type on leaf breakdown rates, associated with the emergence of litter-mixing effects in preserved reaches, highlights the importance of forest fragments to stream biodiversity and functioning in deforested areas. These results show the significant role of invertebrates and stream conditions in leaf breakdown within agricultural areas. They also emphasize the complexity of leaf breakdown and the importance of leaf traits and environmental conditions in this process.