Plant species is more important than urbanization for leaf litter breakdown in a semi-arid river

Leaf litter breakdown plays a crucial role in detrital-based ecosystems, and understanding the factors that influence this process is essential, particularly in data-poor semi-arid riparian zones. This study investigated the influence of land use (upstream and downstream of an urban area) on the decomposition of leaf material from common species in the area (Erythrina velutina, Anacardium occidentale, Tabebuia aurea, Croton sonderianus, and Hymenaea courbaril). Litter bags (single-species, fine and coarse mesh) containing senescent leaves were used to evaluate invertebrate density and richness, shredder and scraper abundance, and litter mass loss after oven drying. Leaf litter with high nutrient content and a low C:N ratio decomposed significantly faster than more recalcitrant litter, likely due to enhanced microbial and invertebrate colonization. Also, litter breakdown was higher when invertebrates had access to leaf material. The effect of invertebrate exclusion was pronounced for high-quality litter, where invertebrate scrapers (Thiaridae, Lymnaeidae, and Planorbiidae) seemed to play a central role in litter fragmentation. Urbanization significantly influenced breakdown rates, but its effects were contingent on litter quality and invertebrate access. Litter breakdown was higher at location under the influence of urbanization, likely due to increased nutrient availability and microbial activity. Ultimately, strong interactions were observed between litter quality, invertebrate access, and urbanization, with the urban effect being most pronounced for high-quality litter, while invertebrate-mediated effects were also stronger for high-quality litter, creating a complex and dynamic ecological condition in the studied semi-arid river.