Warming-acidification synergy amplifies plastisphere-mediated nitrous oxide emissions

Climate warming, acidification, and plastic pollution converge to create unrecognized feedback in the nitrogen cycle. Here, we demonstrate that these anthropogenic pressures synergistically amplify emissions of nitrous oxide (N₂O), from plastic waste in a lake ecosystem. A factorial mesocosm study reveals that combined warming (28 °C) and acidification (pH 6.0) synergistically enhance N₂O emissions from plastic substrates by accelerating nitrogen transformations, depleting ammonium and nitrate while transiently accumulating nitrite. This response is governed by polymer type, with the plastisphere assembled on polylactic acid (PLA) sustains significantly higher (up to 78%) emissions than on polyethylene (PE). A significant temperature and acidification interaction (p < 0.001) confirms synergism, with the combined effect exceeding additivity by 132 μg N g^-1 MLVSS h^-1 for PLA and 36.2 μg N g^-1 MLVSS h^-1 for PE. Bacterial-dominated communities produce the highest N₂O (1182.9 μg N g^-1 MLVSS h^-1 from PLA at pH 6.0 and 28 °C), while acetylene inhibition corroborates this trend, with PLA emissions 49% higher than PE. Mechanistically, the synergy reassembles the plastisphere microbiome into efficient, cooperative networks, enriching keystone N₂O-producing denitrifiers (e.g., Thauera (Aminoaromatica MZ1T), Pseudomonas Stutzeri) and enhancing electron transfer efficiency. This community shift creates a decisive genetic constriction, upregulating the nirS gene while suppressing the N₂O-reducing nosZ gene. Our findings position plastic waste as a climate-sensitive biogeochemical reactor, creating feedback between plastic pollution and anthropogenic climate forcing.