PBAT Microplastics Modulate Oxidative Stress and Plant–Fungus Interactions in Wheat Under Metolachlor Exposure

Microplastics (MPs) and pesticides increasingly co-occur in agricultural ecosystems, where they may jointly affect plant physiology and plant–microorganism interactions. This study investigated the individual and combined effects of biodegradable poly(butylene adipate-co-terephthalate) (PBAT), the herbicide metolachlor (MET), and the beneficial fungus Trichoderma harzianum KKP 534 on wheat (Triticum aestivum). Plant growth, physiological responses, chlorophyll content, cell membrane damage, antioxidant enzyme activities and selected metabolomic and lipidomic biomarkers were evaluated. High PBAT concentrations negatively affected wheat growth by reducing root and shoot length and increasing oxidative stress, as evidenced by elevated TBARS levels, increased antioxidant enzyme activities (POD, GST, CAT, and SOD), and enhanced membrane damage. Metabolomic and lipidomic analyses further revealed stress-associated changes in amino acid metabolism and membrane lipid remodelling. PBAT also adsorbed MET and 2,4-di-tert-butylphenol (DTBP), potentially altering their bioavailability and environmental behaviour. Although T. harzianum KKP 534 promoted plant growth and enhanced antioxidant responses under control conditions, these beneficial effects were attenuated in the presence of PBAT MP. The results suggest that biodegradable microplastics may influence plant–microbe interactions and modify pesticide dynamics under controlled conditions, highlighting the need for further studies in soil-based systems.