Nonylphenol causes shifts in microbial communities and nitrogen mineralization in soil microcosms

The aims of this work was to investigate, in soil microcosms, the effects on soil microbial community structure and function of increasing concentrations of 4-Nonylphenol (NP). The lasts is a product of degradation of NPEOs (Nonylphenol polyethoxylates) with a known toxic and estrogenic capacity able to disrupt animal's hormonal systems. The effect of increasing concentrations of NP (0, 10, 30, 90, and 270 mg NP kg⁻¹ of dry soil) in soil microcosms in three sampling dates (28, 56, and 112 days) over soil microbial activity and function were assessed. Soil microbial activity was estimated by microbial ATP content, and both bacterial and fungal communities composition were estimated using the terminal restriction fragment length polymorphism technique (T-RFLP). Abundance of ammonia-oxidizing bacteria (AOB) was estimated by qPCR of gene encoding for the bacterial ammonia-monoxygenase (amoA). Changes in biologically mediated soil properties were also assessed, namely water-soluble NH⁺ ₄, NO⁻ ₂ and NO⁻ ₃ content, the two last allowing the assessment of mineralization rates. NP-spiking had some unexpected impacts on microbial community structure and functions, since (i) impacted both bacterial and fungal communities structure at the highest NP concentration tested, bacterial communities were resistant to lower concentrations, while fungal communities were increasingly impacted until the end of the incubation at day 112; (ii) no community structure resilience was observed in bacteria at the highest NP concentration nor for fungi at any concentration; (iii) microbial activity decreased with NP after 28 and 56 d, but increased in the last sampling at the highest concentrations tests, coupled to an enrichment in AOB taxa after 56 and 112 days, that at least partly explain also explain the observed speed up of nitrification rates.