Polystyrene nanoparticles intensify the algae-mediated negative priming effect on leaf litter decomposition

The potential threat of nanoplastics on the heterotrophic decomposition of leaf litter lies in their impact on microbial activity and community structure in streams. Therefore, it is crucial to understand the interactions between benthic algae and microbial decomposers when assessing the functioning of stream ecosystems. However, the potential influence of benthic algae on the response of heterotrophic decomposers to nanoplastics remains unknown. This study investigated the interactions between benthic algae and heterotrophic microbial decomposers in the presence of polystyrene nanoparticles (PS-NPs), focusing on their role in leaf litter decomposition and nutrient cycling. The microcosm experiment demonstrated a negative priming effect of benthic algae on leaf decomposition in the absence of PS-NPs. In contrast, the algae-mediated negative priming effect was significantly intensified under PS-NP exposures, decreasing the decomposition rate by 21.3 %. During the various ecological processes, PS-NP exposures significantly reduced the algal biomass and dissolved organic carbon, which in turn disrupted the transfer of labile carbon from benthic algae to heterotrophic microbial decomposers and consequently impeding leaf decomposition process. Additionally, the synergistic effect of benthic algae and PS-NPs decreased the fungal diversity and undermined the dominance of functional genera (i.e., Setophaeosphaeria and Tetracladium) within the microbial decomposer community. In summary, this study offers innovative insights into the interactions among microbial communities colonizing streambed substrates under plastic pollution, highlighting the ecological implications of nanoplastic detrimental influences on aquatic ecosystems.