Soil denitrification stimulated by macroplastics in maize cultivation

Macroplastics (plastic debris > 2 cm) represent an understudied but increasingly prevalent pollutant in agricultural soils, where they may disrupt nitrogen (N) cycling through physical interference with soil structure, altered microbial communities, and changes in nutrient dynamics. While extensive research has focused on microplastics (< 5 mm), the impacts of macroplastics remain poorly understood in maize cultivation. Hence, this study aimed to investigate how macroplastics (> 2 cm) impact soil-plant N variations, maize performance, and microbial-mediated N transformations in the globally promoted maize-based (maize-soybean) intercropping systems through mesocosm and field experiments. While macroplastics minimally affected aboveground maize morphology and yield, they significantly inhibited root development. Soil NO₃^--N concentrations reduced, while nitrite reductase activity and ¹⁵N retention increased, indicating reduced N uptake by maize and accumulation of unused fertilizer in the macroplastic-treated soils. Notably, denitrifying bacteria and functional genes in the denitrification pathway became more abundant, suggesting heightened potential for N loss. Overall, macroplastics exposure did not alter intercropped maize growth but created soil conditions that could stimulate N loss from the soil-maize system via denitrification. Controlling the denitrification reaction should improve N use efficiency and enhance crop yield in macroplastic-polluted agroecosystems.