Detritivore identity modulates effects of nutrient enrichment and a common fungicide presence on leaf litter decomposition and fungal community.

Understanding the interaction of biotic and abiotic factors on ecosystem function is crucial for freshwater ecosystem management, However, the influence of nutrient enrichment, fungicide presence, and detritivore identity on leaf litter decomposition and associated fungal communities remains poorly understood. We conducted a microcosm experiment to examine: 1) the individual and combined effects of nutrient enrichment and a common fungicide on leaf litter decomposition and fungal communities; and 2) how two types of detritivore invertebrates (scrapers vs. shredders) influence these effects. After 35 days, we assessed: 1) leaf litter decomposition, dissolved organic carbon (DOC) production, and the activities of extracellular enzymes; and 2) the diversity, community structure, and co-occurrence networks of fungal communities. We found that both fungicides and nutrient enrichment increased enzymatic activity but did not significantly impact fungal diversity. However, fungicides changed fungal community structure and reduced detritivore-mediated decomposition and DOC production, while nutrient enrichment had the opposite effect. In combination, nutrient enrichment mitigated the negative effects of fungicides on fungal co-occurrence network stability and decomposition. We found that detritivore identity selectively influenced fungal taxa, resulting in distinct co-occurrence patterns under different stressors. The effects of nutrient enrichment and/or fungicide on leaf litter decomposition also depended on detritivore identity. This research underscores the pivotal role of detritivore identity and the interplay of biotic and abiotic factors in shaping fungal communities and modulating leaf litter decomposition, particularly in multiple stressors settings, and its implications for effective management and biodiversity conservation.