Drought Amplifies Polymer-Specific Microplastic Toxicity in Maize by Reshaping Soil-Plant-Microbe Interactions

Microplastics and drought are important costressors in agricultural systems, yet their polymer-specific interactions in soil-plant-microbe systems remain insufficiently understood. This study compared the effects of polyethylene (PE) and biodegradable poly(butylene adipate-co-terephthalate) (PBAT) on maize under drought. Drought reduced maize biomass (59.5%) and gas exchange (transpiration by 36%, stomatal conductance by 80%). MPs intensified these effects, particularly under PBAT, where transpiration declined by 86% and biomass reduction reached 81%. Under drought, PBAT also enhanced oxidative stress. In soil nitrogen dynamics, PBAT increased nitrate under drought by 16%, reflecting enhanced nitrification and reduced plant N uptake linked to microbial responses to biodegradable carbon inputs, whereas PE showed no such increase. Both MPs suppressed urease activity, indicating disrupted N transformation. Rhizosphere metabolomics and microbial analyses revealed shifts in carbon metabolism and drought-tolerant microbial taxa under combined stress. Overall, drought was the dominant stressor, while polymer type modulated soil-plant-microbe interactions and stress responses.