Vulnerability of Brassica oleracea L. (cabbage) grown in microplastic-contaminated soil to extreme climatic events associated with freeze-thaw

Climate change and environmental pollution have increased the frequency and severity of extreme weather events, exposing plants to multifactorial stress conditions that are poorly understood. While extensive research has explored plant responses to individual stress factors, the impact of combined stresses—such as microplastic (MP) contamination and freeze-thaw cycles—remains largely unexamined. This research investigated how soil microplastic pollution affects the freezing tolerance of cabbage (Brassica oleracea L.), a crop vulnerable to unexpected frosts. Seedlings were grown in soils containing varying MP concentrations (0 %, 2 %, 5 %, and 10 % w/w), and their physiological responses to freezing events (-2.5°C and −3.5°C) were assessed. Our findings revealed that although MP particles were not detected in leaf tissues, MP contamination significantly reduced freezing tolerance in a dose-dependent manner. Plants grown in 10 % MP-treated soil exhibited higher membrane damage, as indicated by increased ion leakage and malondialdehyde levels, and showed more severe oxidative stress, with elevated superoxide (O₂^•-) and hydrogen peroxide (H₂O₂) accumulation. These stress responses corresponded with suppressed antioxidant enzyme activities, including catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD). Principal component analysis (PCA) demonstrated distinct physiological patterns between control and MP-treated plants, emphasizing the disruptive impact of MP pollution on stress resilience. This study provides the first empirical evidence that soil microplastic contamination compromises plant tolerance to freeze-thaw cycles, highlighting an overlooked risk to crop performance in changing environmental conditions and calling for further research into the long-term ecological consequences of terrestrial MP pollution.