Effects of perfluoroalkyl acids on nitrogen release, transformation and microbial community during the debris decomposition of Alisma orientale and Iris pseudacorus

The release of nutrients into water during debris decomposition is a serious concern, leading to severe environmental pollution. To understand the effects of extensively present emerging contaminants (such as perfluoroalkyl acids (PFAAs)) on the nitrogen (N) release and transformation, the concentration dynamics of different N species in surrounding water and changes in microbial communities on biofilm during the 70-days decomposition of two typical submerged macrophyte (Alisma orientale and Iris pseudacorus) debris were studied. The results showed that large amounts of N species (especially organic and ammonium N) were released during decomposition. PFAAs with a low concentration (1 μg/L) could stimulate total N (TN) release, whereas PFAAs with a high concentration (≥ 10 μg/L) might have inhibited TN release. Higher intensities of ammonification, nitrosification, and denitrification, but lower intensities of nitrification were observed in water in the presence of PFAAs. Microbiota associated with organic matter hydrolysis, nitrification and denitrification, as well as PFAA degrading/tolerant bacteria, were beneficial and might have occupied dominant states. Redundancy analysis showed that PFAAs were positively associated with the amounts of nitrate, denitrifiers, and azotobacteria but negatively correlated with the TN, ammonia, nitrite, organic N, and nitrosobacteria amounts (p = 0.0002). The complete N metabolism pathway was identified using PICRUSt and KEGG. Functional genes related to ammonification (0.76‰–2.16‰), N reduction (3.43‰–5.05‰), and assimilation (0.81‰–2.16‰) were more abundant than others in all treatments. This study provides a more comprehensive understanding of N cycling during debris decomposition under the increasingly intractable threat of emerging contaminants in aquatic ecosystems.