Nitrogen and phosphorus addition mitigates microplastic community impacts on coastal saline-alkaline wetland ecosystems

Microplastic community (MPC)-composed of diverse sizes (150-3000 μm) and polymer types (e.g., low-density polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride)-pose substantial threats to coastal saline-alkaline wetland ecosystems, while nitrogen (N) and phosphorus (P) fertilization is implemented as a key restoration measure. However, the impacts of N and P inputs on soil microbial communities, plant productivity, and ecosystem stability within MPC-coexisting environments remain largely unknown. To address this, we conducted a 30-day microcosm experiment to examine the effects of MPC alone or combined with N and/or P on soil physicochemical properties, microbial composition, diversity, co-occurrence networks, plant productivity, and ecosystem stability. Results indicate that MPC combined with N induced soil acidification while increasing soil organic matter, available P, and ammonium-N, whereas combined N and P inputs enhanced alkaline phosphatase activity. Nutrient inputs with MPC altered bacterial composition, and P addition benefited microbial community diversity. Both MPC alone and MPC with N and P increased network complexity. Notably, MPC enhanced plant productivity, while combined N and P inputs substantially improved soil and plant stability. Collectively, soil MPC diversity and complexity contribute to enhanced plant productivity, while N and P inputs mitigate the impacts of MPC contamination-specifically by optimizing soil enzyme activity (e.g., ALP), promoting microbial diversity and network complexity, and balancing soil C:P stoichiometry-thereby mitigating MPC impacts on the soil-plant system in coastal saline-alkaline wetlands.