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Polymer-Specific Effects of Microplastics on Sweet Potato Performance and Soil Enzyme Activities
Summary
A controlled 50-day experiment found that polystyrene, polyethylene, and polypropylene microplastics have markedly different effects on sweet potato growth, nutrient uptake, soil enzyme activity, and metabolomic profiles, with polymer type determining whether outcomes are beneficial or harmful. These polymer-specific differences show that microplastic soil contamination cannot be treated as uniform, posing complex and unpredictable risks to staple food crop production.
Microplastics (MPs) are emerging soil contaminants with potential to disrupt plant-soil interactions, yet their impact on staple crops like sweet potato (Ipomoea batatas) remains poorly understood. This study investigated the effects of polystyrene (PS), polyethylene (PE), and polypropylene (PP) MPs at low (0.1%) and high (1%) concentrations on sweet potato growth, metabolism, and soil enzyme activities. Sweet potato seedlings were grown in controlled conditions for 50 days, with MPs mixed into soil. PE and PP MPs significantly enhanced shoot length (up to 30.52%), root length (up to 47.65%), and biomass (up to 134.5%), while PS MPs showed neutral or inhibitory effects. PE MPs increased chlorophyll content (13.48%) and nutrient uptake (Zn: + 53.3%; Mg: + 71.3%), whereas PS MPs reduced chlorophyll (–10.78%) and increased oxidative stress (MDA: + 21.4%). Soil enzyme activities (amylase, phosphatase) decreased under all MPs, with PS causing the strongest inhibition (amylase: –82.8%). Metabolomic profiling revealed 41 significantly altered metabolites, with PE MPs promoting osmoprotective and energy-related pathways, PS MPs inducing metabolic constraints, and PP MPs triggering stress-tolerant adjustments. These polymer-specific effects highlight MPs’ complex influence on soil physicochemical properties, nutrient cycling, and plant physiology. These polymer-specific effects highlight the risk of MPs to agroecosystem health, emphasizing monitoring in staple crop systems to inform sustainable mitigation.