Multiple stressors may pose greater risks to macrophyte community dynamics by driving complex and unanticipated higher-order interactions.

Freshwater ecosystems play a pivotal global role in water security and ecosystem services, but are increasingly threatened by multiple stressors, particularly emerging contaminants. These contaminants are in proximity to human activities and tend to accumulate in sediments, which further amplifies their ecological impacts on freshwater ecosystems. Nevertheless, most studies have focused on the effects of single or pairwise stressors, leaving the effects of complex higher-order interactions on macrophyte communities scant. Here, we conducted a full-factorial experiment using 96 glasshouse mesocosms in 10 L systems containing two macrophyte species (Lemna minor and Spirodela polyrhiza) maintained in a controlled glasshouse environment to investigate the single and higher-order interactive effects of the three emerging contaminants, including microplastics, antibiotics, and antiviral drugs, on two common free-floating macrophytes and their interactions. Our results show that individual and combined stressors cause species-specific responses in free-floating macrophytes, thereby directly or indirectly altering community dominance patterns. Multiple stressors mainly showed antagonistic interactions, triggering negative feedback regulation that alleviated macrophyte growth inhibition. And the feedback is context-dependent, as changes in environmental conditions and stressor combinations may reverse these feedback patterns, potentially enhancing ecological toxicity. Our findings highlight that the inherent complexity and unpredictability of higher-order interactions among multiple stressors can heighten risks to macrophyte communities. We advocate that evaluations of multiple stressors in freshwater ecosystems should integrate context-dependent responses, stressor interactions, and feedback due to redundancy and compensatory dynamics. Future studies should incorporate both biotic and abiotic stressors across multiple gradients and higher ecosystem levels, accounting for non-linear and context-dependent responses.