LAUSR

Urbanization has dramatically destabilized crucial ecosystem functions through extensive land‐use changes, habitat fragmentation, and modified species compositions. However, the mechanisms through which urbanization affects river ecosystem multifunctionality (EMF)—the simultaneous performance of multiple ecosystem functions—remain largely unknown. This study evaluated the impact of urbanization on EMF using macroinvertebrate community data collected from 83 sampling sites across the Yangtze River Delta, China (30°47′N–32°02′N, 119°55′E–121°20′E). We investigated the pathways by which urbanization change ecosystem multifunctionality, including: (1) biotic (such as biodiversity) and abiotic (such as water quality) pathways, (2) taxonomic diversity and functional diversity, and (3) rare species compared to common species. Partial Least Squares Path Modeling revealed that urbanization negatively impacted EMF through both biotic (macroinvertebrate biodiversity) and abiotic (total dissolved solids, salinity, and conductivity) pathways, with the former playing a dominant role. Taxonomic diversity emerged as a stronger positive predictor of EMF than functional diversity. Moreover, the taxonomic diversity was positively correlated with consumer biomass and photosynthetically active radiation and negatively with nutrient concentration. We further showed stronger effects of rare than common species in maintaining EMF. Our study fills a gap in the mechanistic understanding of river ecosystem multifunctionality in plain river networks under urbanization and informs strategies for sustainable urban development. We recommend that conservation efforts in urban areas should prioritize the protection of taxonomic diversity and rare species of macroinvertebrates.