Abstract
The progress of dissimilatory iron(III) reduction is widespread in natural environments, particularly in anoxic habitats; in fact, wetland ecosystems are considered as “hotspots” of dissimilatory Fe(III) reduction. In this study, we conducted soil slurry and microbial inoculation anaerobic incubation with glucose, pyruvate, and soluble quinone anthraquinone-2,6-disulphonate (AQDS) additions in freshwater marsh and meadow wetlands in the Sanjiang Plain, to evaluate the role of carbon addition in the rates and dynamics of iron reduction. Dissimilatory Fe(III) reduction in marsh wetlands responded more quickly and showed twice the potential for Fe(III) reduction as that in meadow wetland. Fe(III) reduction rate in marsh and meadow wetlands was 76% and 30%, respectively. Glucose had a higher capacity to enhance Fe(III) reduction than pyruvate, which provides valuable information for the further isolation of Fe reduction bacteria in pure culture. AQDS could dramatically increase potential Fe(III) reduction as an electron shuttle in both wetlands. pH exhibited a negative relationship with Fe(III) reduction. In view of the significance of freshwater wetlands in the global carbon and iron cycle, further profound research is now essential and should explore the enzymatic mechanisms underlying iron reduction in freshwater wetlands.
Highlights
Iron is the most abundant redox-active element in the Earth’s crust, and iron oxides occur ubiquitously in natural environments [1]
The extremely high rates observed after the addition of AQDS in our study indicates that iron reduction was more limited by the availability of electron acceptors than by energy or mineral nutrients; this observation was reported by Lipson et al [6] in an Arctic peat soil
Marsh wetlands exhibited higher Fe(III) reduction rates than meadow wetlands due to differences in soil structure, plant roots and the concentration, and phase of Fe(III) minerals
Summary
Iron is the most abundant redox-active element in the Earth’s crust, and iron oxides occur ubiquitously in natural environments [1]. Under strict and facultative anaerobic conditions, dissimilatory iron reduction occurs when microorganisms conserve energy through redox reactions without assimilating iron into its biomass [4]. Given the abundance of iron, iron reduction-oxidation reactions have the potential of supporting substantial microbial populations in soil and sediments. Wetlands soils are often dominated by fluctuating redox reactions and abundant organic carbon, which provide an ideal model with which to study the relationship between carbon and iron. Dissimilatory Fe(III) reduction has been proven to be the dominant pathway for the mineralization of anaerobic organic matter in many aquatic soils and sediment. Another study reported that microbial iron reduction along the inundation gradient in the Min River Estuary accounted for 20–89% of the mineralization of anaerobic organic matter [7]
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