Ammonia level influences the assembly of dissimilatory nitrate reduction to ammonia bacterial community in soils under different heavy metal remediation treatments

Abstract

Heavy metal remediation treatments might influence functional microbial community assembly. Dissimilatory nitrate reduction to ammonia (DNRA) contributes to the nitrogen retention processes in soil ecosystems. We assumed that remediation might reduce heavy metal toxicity and increase some available nutrients for the DNRA microbes, thus balancing the deterministic and stochastic process for DNRA community assembly. Here, we investigated the process of DNRA bacterial community assembly under different heavy metal remediation treatments (including control, biochar, limestone, rice straw, rice straw + limestone, and biochar + limestone) in an Alfisol soil. The abundance of DNRA bacteria diverged across treatments. The α-diversity of the DNRA bacterial community was correlated with pH, available phosphorus (AP), ammonium (NH4+), and extractable Fe (EFe). Metal Cd and Fe significantly affected the abundance of the nrfA gene. The β-diversity was associated with pH, NH4+, and EFe. Deterministic processes dominantly drove the assembly processes of the DNRA bacterial community. NH4+ level played an essential role in the assembly processes than the other soil physicochemical properties and metal availability. High, moderate, and low levels of NH4+ could advocate stochastic process plus selection, heterogeneous selection to stochastic process, and heterogeneous selection, respectively. Network analysis highlighted a predominant role of NH4+ in regulating DNRA bacterial community assembly. However, the relative abundance of modules and some keystone species also were influenced by pH and EFe, respectively. Therefore, the DNRA bacterial community assembly under different heavy metal remediation treatments in this study was dominantly driven by nitrogen availability. pH, phosphorus, and metal availability were auxiliary regulators on DNRA bacterial community.