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Effects of Fe oxide on N transformations in subtropical acid soils.

ABSTRACT: Subtropical ecosystems are often characterized by high N cycling rates, but net nitrification rates are often low in subtropical acid soils. NO3(-)-N immobilization into organic N may be a contributing factor to understand the observed low net nitrification rates in these acid soils. The effects of Fe oxide and organic matter on soil N transformations were evaluated using a (15)N tracing study. Soil net nitrification was low for highly acidic yellow soil (Ferralsols), but gross ammonia oxidation was 7 times higher than net nitrification. In weakly acidic purple soil (Cambisols), net nitrification was 8 times higher than in Ferralsols. The addition of 5% Fe oxide to Cambisols, reduced the net nitrification rate to a negative rate, while NO3(-)-N immobilization rate increased 8 fold. NO3(-)-N immobilization was also observed in Ferralsols which contained high Fe oxides levels. A possible mechanism for these reactions could be stimulation of NO3(-)-N immobilization by Fe oxide which promoted the abiotic formation of nitrogenous polymers, suggesting that the absence of net nitrification in some highly acid soils may be due to high rates of NO3(-)-N immobilization caused by high Fe oxide content rather than a low pH.

SUBMITTER: Jiang X

PROVIDER: S-EPMC4342567 | biostudies-literature | 2015 Feb

REPOSITORIES: biostudies-literature

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Effects of Fe oxide on N transformations in subtropical acid soils.

Jiang Xianjun X Xin Xiaoping X Li Shiwei S Zhou Junchao J Zhu Tongbin T Müller Christopher C Cai Zucong Z Wright Alan L AL

Scientific reports 20150227

Subtropical ecosystems are often characterized by high N cycling rates, but net nitrification rates are often low in subtropical acid soils. NO3(-)-N immobilization into organic N may be a contributing factor to understand the observed low net nitrification rates in these acid soils. The effects of Fe oxide and organic matter on soil N transformations were evaluated using a (15)N tracing study. Soil net nitrification was low for highly acidic yellow soil (Ferralsols), but gross ammonia oxidation ...[more]

PMID: 25722059

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Project description:Whole-genome DNA microarray analysis of Geobacter sulfurreducens cells grown on Fe(III)-oxide or Mn(IV)-oxide versus cells grown on soluble Fe(III) citrate indicated that there were significant differences in transcription patterns during growth on the insoluble metal oxides compared to growth on soluble Fe(III). Many of the genes that appeared to be up-regulated during growth on the metal hydroxides were involved in electron transport. The most highly up-regulated genes for both conditions were omcS and omcT, which encode co-transcribed c-type cytochromes exposed on the outer surface of the cell that are known to be required for Fe(III) and Mn(IV)-oxide reduction. Other electron transport genes that were up-regulated on both insoluble metals included the gene coding for the outer membrane c-type cytochrome, OmcG, genes for the outer membrane proteins, OmpB and OmpC, and the gene that codes for the structural protein of electrically conductive pili, PilA. Genes that were up-regulated in cells grown on Fe(III)-oxide but not Mn(IV)-oxide, included outer membrane c-type cytochromes including OmcE, a putative DMSO reductase protein, and proteins from the cytochrome bc1 complex. Electron transport genes that were only up-regulated in Mn(IV)-oxide grown cells included the genes that code for the outer membrane c-type cytochromes, OmcZ and OmcB, the periplasmic c-type cytochrome, MacA, and fumarate reductase. Genetic studies indicated that the c-type cytochrome proteins, PpcH, OmcJ, OmcM, OmcV, MacA, OmcF, OmcI, and OmcQ, and the iron sulfur subunit of the cytochrome b/b6 complex, QcrA, are important for reduction of insoluble Fe(III)-oxides but do not appear to be important for Mn(IV) reduction. These results demonstrate that the physiology of Fe(III) reducing bacteria differ significantly during growth on insoluble electron and soluble electron acceptors and emphasizes the importance of c-type cytochromes in extracellular electron transfer in G. sulfurreducens. Geobacter sulfurreducens cells were grown with acetate (5 mM) provided as the electron donor and either Fe(III) oxide or Fe(III) citrate provided as the electron acceptor. Cells were harvested at mid-log and total RNA was extracted. Total RNA (0.5 μg) was amplified using the MessageAmp II-Bacteria Kit (Ambion, Foster City, CA) according to the manufacturers instructions. Ten micrograms of amplified RNA (aRNA) was chemically labeled with Cy3 (for the control or soluble electron acceptor condition) or Cy5 (for the experimental or insoluble electron acceptor condition) dye using the MicroMax ASAP RNA Labeling Kit (Perkin Elmer, Wellesley, MA) according to the manufacturer’s instructions.

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Effects of Fe oxide on N transformations in subtropical acid soils.

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Effects of Fe oxide on N transformations in subtropical acid soils.

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