Abstract
Iron reduction is an important biogeochemical process in paddy soils, yet little is known about the microbial coupling between nitrogen and iron reduction. Here, we investigated the shift of acetate-metabolizing iron-reducers under long-term nitrogen fertilization using 13C-acetate-based ribosomal RNA (rRNA)-stable isotope probing (SIP) and pyrosequencing in an incubation experiment, and the shift of putative iron-reducers in original field samples were investigated by 16S rRNA gene-based pyrosequencing. During SIP incubations, in the presence of iron(III) oxyhydroxides, more iron(II) formation and less methane production were detected in nitrogen-fertilized (N) compared with non-fertilized (NF) soil. In 13C-rRNA from microcosms amended with ferrihydrite (FER), Geobacter spp. were the important active iron-reducers in both soils, and labeled to a greater extent in N (31% of the bacterial classified sequences) than NF soils (11%). Pyrosequencing of the total 16S rRNA transcripts from microcosms at the whole community level further revealed hitherto unknown metabolisms of potential FER reduction by microorganisms including Pseudomonas and Solibacillus spp. in N soil, Dechloromonas, Clostridium, Bacillus and Solibacillus spp. in NF soil. Goethite (GOE) amendment stimulated Geobacter spp. to a lesser extent in both soils compared with FER treatment. Pseudomonas spp. in the N soil and Clostridium spp. in the NF soil may also be involved in GOE reduction. Pyrosequencing results from field samples showed that Geobacter spp. were the most abundant putative iron-reducers in both soils, and significantly stimulated by long-term nitrogen fertilization. Overall, for the first time, we demonstrate that long-term nitrogen fertilization promotes iron(III) reduction and modulates iron-reducing bacterial community in paddy soils.
Highlights
Iron (Fe) is the most abundant redox-active element on the Earth, microbial iron redox cycling has a fundamental role in environmental biogeochemistry (Weber et al, 2006a)
The shift of putative dissimilatory ironcommunity participating in dissimilatory Fe(III) reducers in original field samples were investigated reduction have been rather limited because of the by 16S rRNA gene-based pyrosequencing to examine unavailability of universal functional gene markers. the relevance between the results obtained from Stable isotope probing (SIP)
We demonstrate that longterm N fertilization promotes iron(III) reduction and modulates iron-reducing bacterial community in paddy soils
Summary
Iron (Fe) is the most abundant redox-active element on the Earth, microbial iron redox cycling has a fundamental role in environmental biogeochemistry (Weber et al, 2006a). Dissimilatory ferric iron [Fe(III)] reduction occurs under anoxic conditions when coupled to other biogeochemical processes, for instance the oxidation of organic matter or hydrogen (H2; Lovley et al, 2004). The reduced ferrous iron [Fe(II)] can be reoxidized under anoxic conditions when coupled to nitrite (NO2À ) or Microorganisms that mediate dissimilatory Fe(III) reduction are phylogenetically diverse (Lin et al, 2007). Numerous dissimilatory iron-reducing microorganisms have been isolated, characterized and identified from paddy soils mainly by culturedependent methods (Wang et al, 2009; Li et al, 2011). Studies on the composition of microbial used. The shift of putative dissimilatory ironcommunity participating in dissimilatory Fe(III) reducers in original field samples were investigated reduction have been rather limited because of the by 16S rRNA gene-based pyrosequencing to examine unavailability of universal functional gene markers. the relevance between the results obtained from SIP
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