Acidification reshapes plastisphere communities to sustain potassium-stimulated N₂O emissions under warming

The plastisphere is a novel anthropogenic habitat in the global nitrogen cycle, yet how agricultural nutrient pollution, acidification, and warming combinedly affect its nitrous oxide (N₂O) fluxes remains unknown. We hypothesized that these stressors amplify emissions from plastic biofilms. A factorial mesocosm experiment exposed biodegradable (PLA) and non-biodegradable (PE) plastics to potassium (K-70 mg/L), acidification (pH 6.0, 6.5), and warming (23°C, 28 °C) under hypoxic conditions, using inhibitors and genomic profiling to identify pathways. PLA consistently sustained higher N₂O emissions than PE, dominated by bacterial denitrification. Potassium and warming elicited a synergistic response, increasing N₂O flux by 58%. While acidification combined with potassium and warming suppressed key functional genes (nirS, nosZ), it selected stress-tolerant consortia, including resilient nirK-type denitrifiers, that sustained the genetic potential for N₂O production. This community adaptation and reduced N₂O reduction capacity (lower nosZ) explain persistent emissions under acidic conditions. Abiotic chemo-denitrification occurred but was an order of magnitude slower than in pure chemical systems. Polymer-specific restructuring occurred, with PLA supporting more diverse consortia and higher genetic potential for nitrogen transformations. Three-way ANOVA confirmed that potassium × warming synergy is significantly modulated by pH (p < 0.001). These findings establish the plastisphere as a significant, unquantified N₂O source, creating a feedback loop between plastic pollution, agriculture, and climate change, necessitating its inclusion in global nitrogen and climate models.