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Impact of Polyethylene and Polylactic AcidMicroplastics on Seed Germination and SeedlingDevelopment of Trifolium repens
Summary
Scientists found that tiny plastic particles in soil—both regular plastic (polyethylene) and "biodegradable" plastic (PLA)—can affect how well clover seeds sprout and grow, with small amounts sometimes boosting germination but larger amounts stunting root growth and reducing water uptake. This matters because it shows that so-called eco-friendly plastics aren't automatically safer for soil and plants, and since these plastics can end up in agricultural soil, understanding their effects on plant growth is a first step toward understanding how they might eventually affect the food we eat.
Microplastics (MPs) are emerging contaminants with uncertain effects on plants, particularly ornamentals. We tested how polyethylene (PE), polylactic acid (PLA), and a constant-total-dose 1:1 (w/w) mixture of PE and PLA (MIX; 25 μm) at 0.1% (w/v), 0.5% (w/v), and 1.0% (w/v) influence seed germination and early growth of white clover (Trifolium repens) in Petri-dish assays. Although these exposure levels exceed typical background levels in bulk soils, they were used to represent worst-case/high-exposure scenarios to elucidate potential mechanisms and effect thresholds in a 7-day assay. Endpoints included germination potential and final germination rate, root traits (radicle elongation inhibition rate and root-to-shoot ratio), seedling biomass (fresh/dry mass), and water content. Responses generally followed a dose-dependent hormetic pattern, with low-dose PE increasing final germination rate, while higher exposures impaired root development and altered biomass allocation. Notably, the high-dose MIX treatment reduced the root-to-shoot ratio by ~37% relative to the control, suggesting disrupted allocation and/or disproportionate root impairment under intense MP stress. Water relations were polymer-specific: PE reduced seedling water content across all tested levels, consistent with physical blockage and/or impaired root water transport, whereas PLA and MIX caused significant declines mainly at higher concentrations. Overall, polymer identity and concentration jointly regulated early establishment, supporting the “low-dose stimulation, high-dose inhibition” framework and underscoring the need to consider both biodegradable and conventional MPs in ecological risk assessment.