Effects of polystyrene microbeads on seed germination, plant growth and nutrient uptake in two landraces of Capsicum annuum L

Agricultural activities are a major source of microplastic (MPs) contamination due to the extensive use of plastic materials in mulching films, irrigation systems, and nursery supplies. According to the FAO, agricultural plastic consumption reached approximately 12.5 million tons in 2021, raising concerns about the accumulation of MPs in soils and their transfer to the soil-plant system and food chain. Increasing evidence indicates that MPs can negatively affect plant physiology, impairing germination, root development, nutrient uptake, and redox homeostasis. Among commonly used polymers, polystyrene (PS) is of particular concern due to its documented phytotoxicity. In this study, we investigated the effects of polystyrene microplastics (PS-MPs, 1 μm), supplied through the culture medium, on two Capsicum annuum L. landraces from southern Italy, Sassaniello-giallo (SY) and Papaccella-gialla (PY). Germination performance, seedling growth, mineral uptake, and oxidative responses were evaluated to assess cultivar-specific sensitivity. PS-MPs negatively affected seedling development in both landraces, reducing biomass accumulation, root length, and leaf area, and inducing oxidative stress. Microscopic observations revealed the presence of MPs or their aggregates in the rhizoderm, root cortex, vascular tissues, and near root hairs, with evident damage to the root apex. Differential responses were observed between landraces: SY showed reduced germination in the presence of MPs, whereas PY exhibited a stimulation of germination, possibly linked to differences in antioxidant capacity. Overall, the observed effects suggest that PS-MPs toxicity is largely driven by physical interactions with plant tissues, leading to impaired physiological processes. These findings highlight the need for further research to clarify the mechanisms underlying MPs-plant interactions.