Synergistic Effects of Thermal Stress and Microplastic Pollution on Seed Germination Under Agricultural Soil Conditions

ABSTRACT Environmental stressors such as heat shock (HS) and microplastics (MPs) can markedly influence seed germination and early seedling development. This study investigated the isolated and combined effects of HS and polyethylene microplastics (PE‐MPs) on the germination of wheat ( Triticum aestivum ) and maize ( Zea mays ). Seeds were exposed to HS at 40°C, 60°C, 80°C, and 120°C for 1, 5, 10, and 15 min, in the presence of PE‐MPs at 0.01, 0.1, and 1% (w/w). Moderate HS significantly enhanced germination ( p < 0.05): wheat showed a 16.32% increase at 40°C for 15 min, while maize increased by 9.80% at 60°C for 10 min relative to the control. In contrast, the combined HS + MPS exposure significantly reduced germination by 8.8%, 15.78%, and 17.54% in wheat, and by 7.10%, 16.04%, and 24.97% in maize. MPs alone produced the strongest inhibitory effect ( p < 0.05), decreasing germination by 17.54%, 26.31%, and 40.42% in wheat, and by 17.89%, 27.11%, and 35.69% in maize at 0.01, 0.1, and 1% (w/w), respectively. Both stressors also delayed germination, as reflected by increased mean germination time (MGT). These results highlight the importance of evaluating multi‐stress interactions in agroecosystems and contribute to improving crop management strategies and food security under climate‐driven environmental change.