Per-fluoroalkyl substances (PFASs) have been widely detected in farmland soils and are understood to pose toxicological threats to soil microbiomes and crop safety. Meanwhile, farmland ecosystems have experienced increasing nitrogen loading caused by soil fertilization. Yet it is still unclear how nitrogen additions affect soil's microbial responses to PFASs. In this study, using a laboratory-based ecological experiment, we assessed the microbial availability of PFASs in soils receiving ammonium, nitrate, and urea nitrogen amendments by quantifying the translocation factors of PFASs from soil particle to soil extracellular polymeric substances (EPS). Our results showed that nitrogen, specifically ammonium, significantly increased the PFASs' microbial availability (p < 0.05). Second, nitrogen fertilization in PFASs-polluted soils decreased the microbial community diversity and stability at the structural, species, and functional levels (p < 0.05). For soil microbial activities, nitrogen enhanced the activity of superoxide dismutase (SOD) while it inhibited the catalase (CAT) and peroxidase (POD) (p < 0.01). Congruently, PFASs, as well as the nitrate and nitrite nitrogen, were shown to be the predominant abiotic drivers regulating the soil fungal succession (p < 0.05), while bacteria were mostly regulated by dissolved organic carbon (DOC) (p < 0.01). Furthermore, we revealed that the nitrogen cycling gene hmp (dominates the transformation from NO to NO3-) was the hub gene integrating the microbially available PFASs and the soil nitrogen cycling processes (p < 0.01), indicating that hmp could be the core regulator affecting the accumulation of PFASs in soil EPS. Our study highlighted that decreasing ammonia's amendments could mitigate China's national initiatives to reduce nitrogen fertilization in farmlands, reduce the PFASs' availability to the soil microbiome, and protect the microbial community stability in soil.
Keywords: Microbial availability; Nitrogen addition; Per-fluoroalkyl substances; Soil extracellular enzymes; Soil microbial community.
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