Nitrogen availability influences microbial reduction of ferrihydrite-organic carbon with substantial implications for exports of iron and carbon from peatlands

Abstract While iron (Fe) has been proposed to constrain dissolved organic carbon (DOC) export by forming precipitation (Fe-OC) in peatlands, uncertainties remain about the potential interactions between Fe and nitrogen. Such interactions are important for Fe and carbon exports as they can dissolve the Fe-OC through Fe reduction. Here we studied the reduction of ferrihydrite-OC (Fh-OC) following incubation with microbes from agricultural and natural peatlands under differing nitrogen availability, with high-throughput sequencing to identify microbial mechanisms. Our results showed that in agricultural peatlands, high nitrogen levels (>100 mg kg−1) modified the composition and abundance of iron-reducing bacteria, increasing reduction rates of Fh-OC (0.09–0.20 kg Fe day−1 ha−1) above the low N treatments (