The Effect of Different Carbon Sources on Nitrate-Dependent Iron Oxidation Process, Bacterial Diversity, and C Protagonist in Varied Texture Soils

Nitrate-dependent Fe-oxidizing bacteria (NFeOB) are key mediators for carbon (C) and nitrogen (N) cycling in paddy soils. The aim of this study was to explore soil NFeOB community in response to addition of readily available organic C in different soils. The present study used glucose (Glu) and acetate (Ace) as carbon source for anaerobic enrichment cultures of NFeOB from two soils (Danyang (DY) and Qichun (QC)) establishing four treatments: DY-Ace, DY-Glu, QC-Ace, and QC-Glu. Cumulative N₂O emissions from QC soil were 3.06 µg/L in Ace and 2.04 µg/L in Glu treatment. N₂O emissions in DY soil were 65.79 µg/L with Glu treatment and 1.92 µg/L with Ace treatment. CO₂ emissions showed a strong uptake trend and were almost at the same level (mean 139.70 mg/L) for the two different carbon sources. High-throughput sequencing showed that the carbon source was the controlling factor for the microbial abundance and diversity. Simpson and Shannon–Wiener indices indicated higher abundance and diversity in the Ace treatment than that of Glu treatment. Proteobacteria was dominant in all treatments, and at genus level, Cupriavidus was the most abundant. Moreover, higher abundance of Actinobacteria in the DY-Glu treatment resulted in higher N₂O emissions. In short, nitrate-dependent Fe(II) oxidation by Cupriavidus is imperative for CO₂ fixation.