Soil nitrogen availability regulates the warming effect on the priming effect induced by polyhydroxyalkanoate microplastics

Abstract

Soil microplastics (MPs) pollution is a global ecological environment threat. Although biodegradable plastics are designed substitutes for nonbiodegradable plastics, biodegradable MPs in soil is a carbon source that can increase or decrease soil organic matter (SOM) mineralization through priming effect. Soil nitrogen (N) availability can alter the priming effects by orchestrating the microbial growth and metabolism, yet the underlying mechanisms remain elusive, especially under global warming. Based on incubation experiments using long‐term N‐fertilized soils, we found that the polyhydroxyalkanoates (PHA) MPs‐induced priming effect was co‐regulated by the fungal N mining from SOM and bacterial necromass mineral protection of SOM, and warming amplified this phenomenon. The PHA‐induced priming effect ranged from 7% to 45%, highest in soil without N fertilizer input, followed by low‐N and high‐N fertilizer input soils. Warming increased the priming effect by 13%−15% in soil without N, whereas decreased the priming intensity by 2%−3% in high‐N soil. Specifically, warming increased microbial biomass production, and thus carbon use efficiency (CUE) by increasing dissolved organic carbon resulting from PHA decomposition. In soil without N, high CUE promoted fungal dominance, stimulating N mining and SOM loss. In high‐N soil, high CUE promoted bacterial driven necromass accumulation, enhancing SOM stabilization through microbial and mineral carbon pumps. Therefore, N availability in PHA‐contaminated soil modulates microbial community dynamics (bacterial and fungal) under warming, ultimately determining loss and sequestration of SOM. These findings highlight that long‐term N fertilization application can mitigate SOM loss caused by biodegradable MPs pollution, and provide critical insights for industrial and agricultural management.