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Nitrate pollution in fresh water is becoming increasingly serious. In this study, the effects of temperature and graphene oxide materials on the potential functions of denitrification communities in lake sediments were investigated by metagenome. The addition of graphene oxide significantly affected the abundance of denitrification genes such as Nap , Nos , and enhanced the contribution of Pseudomonas , making low temperature and material addition conducive to the denitrification process. Module network implied that low temperature increased the centrality of denitrification in community functions. At low temperatures, graphene oxide enhanced community anabolism by stimulation organic carbon consumption and regulating the gene abundance in the citric acid cycle and the semi-phosphorylation Entner-Doudoroff, thus possibly stimulating extracellular polymeric substances (EPS) synthesis and secretion. In addition, graphene oxide may also regulate the transfer of reducing electrons from NADH to denitrifying enzymes by affecting the gene abundances of complex I and complex IV. [Display omitted] • Graphene oxide led to an increase in the proportion of denitrification genes at 8 °C. • Graphene oxide enhanced community anabolism at 8 °C. • Graphene oxide stimulated EPS synthesis and secretion at 8 °C. • Graphene oxide regulated the transfer of electrons to denitrifying enzymes. [ABSTRACT FROM AUTHOR]

Microbial nitrate reduction can be driven by organic carbon oxidation, as well as by inorganic electron donors, such as reduced forms of sulfur and iron. An apparent inverse oxygen isotope fractionation effect was observed during nitrate reduction in sediment incubations from five sampling sites of a freshwater lake, Hongze Lake, China. Incubations with organic and inorganic electron donor additions were performed. Especially, the inverse oxygen isotope effect was intensified after glucose addition, whereas the incubations with sulfide and Fe2+ showed normal fractionation factors. Nitrate reductase encoding genes, napA and narG, were analysed with metagenomics. Higher napA/narG ratios were associated with higher oxygen fractionation factors. The most abundant clade (59%) of NapA in the incubation with glucose was affiliated with Rhodocyclales. In contrast, it only accounted for 8%–9% of NapA in the incubations with sulfide and Fe2+. Differences in nitrate reductases might explain different oxygen isotope effects. Our findings also suggested that large variance of O‐nitrate isotope fractionations might have to be considered in the interpretation of natural isotope records. [ABSTRACT FROM AUTHOR]