ASHS 2025 Conference

Plastic pollution is an emerging concern for both aquatic and terrestrial ecosystems. Recent studies, primarily focused on cereals and vegetable crops, have demonstrated that nanoplastics (NPs) can enter root tissues and translocate throughout the plant. However, the accumulation and impact of NPs in woody perennial crops, particularly citrus, remain largely unexplored. This study investigated the effects of green, fluorescent polystyrene nanoplastics (PS-NPs) of two particle sizes (20 nm and 50 nm diameter) on citrus root development, nutrient uptake, and root anatomical features. ‘US-942’ citrus rootstock plants were grown under sterile aeroponic conditions and treated with PS-NPs for 15 and 30 days. Root system architecture traits, including total root length, surface area, and number of forks, were analyzed using WinRHIZO™ software. Concurrently, macronutrient and micronutrient concentrations (N, P, K, Mg, S, B, Fe, Cu, Mn) were assessed in plant tissues, and root anatomy was examined using fluorescence and light microscopy. Exposure to 20 nm PS-NPs significantly reduced total root length (–28%), surface area (–31%), and the number of root forks (–35%) at both timepoints compared to controls. Nutrient uptake was also adversely affected, with notable reductions in N, P, K, Mg, and several micronutrients. Microscopic analyses revealed that both PS-NP sizes were retained at the root surface, with no evidence of internalization or translocation into root tissues. However, alterations in epidermal and cortical cell layers suggested structural stress responses, despite the development of intact apoplastic barriers near root tips. These findings highlight the potential phytotoxic effects of PS-NPs on citrus, particularly at smaller particle sizes, and suggest that while internal uptake may be limited in woody perennials, surface-level interactions may disrupt root development and function. This study contributes to a growing understanding of nanoplastic interactions in horticultural tree crops and raises important questions regarding long-term impacts on soil-plant systems.