Effects of pH and polycyclic aromatic hydrocarbon pollution on thaumarchaeotal community in agricultural soils

Purpose Thaumarchaeota is an ecologically relevant archaeal phylum which may significantly contribute to global nitrogen cycling. Thaumarchaeotal abundance, composition, and activity can be changed by soil pH and pollutants such as toxic metals. This study aims to examine the responses of thaumarchaeotal community to soil pH variation and polycyclic aromatic hydrocarbon (PAH) pollution which may co-occur in agricultural soils. Materials and methods Field soil samples were collected from agricultural land impacted by both acidification and PAH contamination. Thaumarchaeotal abundance and composition were assessed using molecular approaches targeting 16S rRNA or amoA genes and were linked to environmental factors by correlation and canonical correspondence analysis (CCA). To evaluate the short-term responses of Thaumarchaeota to PAHs, additional soil microcosms amended with either three selected PAHs were established. Changes in thaumarchaeotal communities during the incubation were monitored. Results and discussion A significant correlation between thaumarchaeotal gene abundance and soil pH was observed within field samples, with the I. 1a-associated group enriched when pH <5.0. CCA suggests that the community variation was primarily related to soil pH. In contrast, the effects of PAHs were minimal. In soil microcosms, high concentrations of PAHs persisted after the 4-week incubation. Independent of the PAHs added, thaumarchaeotal amoA abundance slightly increased and the compositions were stable at the end of the incubation. This might be associated with the pollutants bio-availability and potential microbe-PAH interactions in the soil. Conclusions Soil pH variation strongly shapes the agricultural soil thaumarchaeotal community, whereas PAH effects appear to be marginal even in the presence of high concentrations of pollutants. The complicated interaction between soil matrix, pollutants, and Thaumarchaeota requires further study.