胡荣桂团队：水稻土中亚铁氧化对硝酸盐还原过程及其氧化亚氮排放的影响

华中农业大学资源与环境学院胡荣桂团队探究了水稻土中亚铁氧化对硝酸盐还原过程及其氧化亚氮排放的影响。相关成果发表于期刊 Geoderma （ IF =4.848）和 ACS Earth and Space Chemistry（ IF =3.418）。

两篇论 均被2021年最新发表在 Nature Reviews Microbiology（ IF =34.209）的综述论 An evolving view on biogeochemical cycling of iron 引用。

Highlights

?Fe(II) oxidation coupled to denitrification exists in flooded paddy soils.

? Fe(II) regulated N2 O emissions via donating electrons to denitrification.

? High level of Fe(II) facilitated efficient denitrification and low N2 O emissions.

Abstract

Paddy soils are important source of nitrous oxide (N 2 O), which production is mainly regulated through redox processes and electron transfer. Ferrous iron [Fe(II)] oxidation coupled to denitrification is ubiquitous in paddy soils, which could affect N 2 O production via donating electrons to denitrification. To clarify the effects of Fe(II) oxidation on denitrification and N 2 O emissions, a flooding experiment was conducted in two paddy soils with contrasting Fe(II) levels. The soil with high Fe(II) concentration emitted less N 2 O than did the other soil with low Fe(II) concentration. Nitrate addition decreased Fe(II) concentration and stimulated N 2 O production in both soils, suggesting that Fe(II) oxidation is coupled to denitrification. The stoichiometry of electron transfer between nitrate reduction and Fe(II) oxidation demonstrated that the percentage of electrons contributed by Fe(II) to denitrification accounted for 16.2% and 32.9%, and the ratios of the electrons donated by Fe(II) to the electrons accepted by nitrate for N 2 O production were 43.7% and 130.7% in the two soils with low and high Fe(II) concentration, respectively. The ratio beyond 100% implies that the electrons donated by high Fe(II) concentration exceed the electron demand for N 2 O production, which lead to the further reduction of N 2 O to N 2 . In conclusion, Fe(II) oxidation coupled to denitrification affects N 2 O emissions via electron donation, and Fe(II) in a high concentration bears great potential for efficient denitrification and low N 2 O emissions from paddy soils.

氧化亚氮(N 2 O)是重要的温室气体，也是主要的臭氧层破坏物质。因周期性的淹水落干和频繁的氮肥施用等农业措施管理，稻田土壤对大气N 2 O排放有着重要贡献。N 2 O的产生主要受氧化还原和电子转移过程控制。在淹水稻田土壤中亚铁[Fe(Ⅱ)]氧化与硝酸盐还原耦合过程很容易发生，Fe(Ⅱ)可能通过贡献电子给硝酸盐还原过程从而影响N 2 O排放。为了阐明Fe(Ⅱ)氧化对反硝化作用和N 2 O排放的影响，对亚铁含量不同的两组稻田土壤进行了淹水实验。结果表明：高Fe(Ⅱ)含量的土壤N 2 O排放少于低Fe(Ⅱ)含量的土壤。硝酸盐的添加均降低了两组土壤中Fe(Ⅱ)浓度并促进了N 2 O的排放，这表明Fe(Ⅱ)氧化与硝酸盐还原耦合过程的发生。通过化学计量计算硝酸盐还原与Fe(Ⅱ)氧化之间的电子转移，结果表明：在高Fe(Ⅱ)含量和低Fe(Ⅱ)含量的土壤中，Fe(Ⅱ)对反硝化作用的电子贡献比分别为16.2％和32.9％，且在两土壤中Fe(Ⅱ)氧化捐赠的电子与硝酸盐还原生成N 2 O接受的电子的比率分别是43.7％和130.7％。其中，大于100％的比率意味着高含量Fe(Ⅱ)贡献的电子超过硝酸盐还原生成N 2 O所需要的电子，这可导致N 2 O进一步还原生成N 2 。总之，Fe(Ⅱ)氧化可通过捐赠电子调节反硝化过程进而影响N 2 O排放，稻田土壤中高含量的Fe(Ⅱ)对高效反硝化作用和低N 2 O排放有着巨大的潜力。

Abstract

Atmospheric nitrous oxide (N 2 O) causes global warming and ozone depletion. Nitrate and nitrite reduction are the main sources for N 2 O emission in anoxic environments including both microbial (denitrification) and abiotic reactions (chemodenitrification), besides nitrification in oxic habitats. In flooded paddy soils, substantial concentrations of Fe(II) and nitrite are available, potentially triggering chemodenitrification. It is currently unknown to what extent chemodenitrification contributes to N 2 O emissions in such environments. We conducted anoxic microcosm experiments with two paddy soils that differ in natural Fe(II) and organic carbon content. We amended them with nitrite or nitrate and quantified N 2 O emissions. In sterilized soils, nitrite and not nitrate was abiotically reduced, pointing toward chemodenitrification. In microbially active soils, nitrate reduction was accompanied by nitrite accumulation, ammonium production, and N 2 O emission, implying the co-occurrence of denitrification, dissimilatory nitrate reduction to ammonium (DNRA), and chemodenitrification. N 2 O emissions from chemodenitrification accounted for 6.8–67.6% of the total N 2 O emissions, depending on the concentrations of Fe(II), nitrite, nitrate, and organic carbon, and the N 2 O emission rate from abiotic reactions was up to 2.4 mg N kg –1 d –1 . Elevated Fe(II) levels in soils facilitated nitrite accumulation, chemodenitrification, and high abiotic N 2 O emission (up to 42.9%). In low organic carbon soil, more N 2 O was emitted by chemodenitrification in nitrite-amended setups (20.5% of total N 2 O emission) compared to nitrate-amended setups (6.8%). High organic carbon content in soils indirectly enhanced the proportion of abiotic N 2 O production (up to 67.6%), potentially favoring DNRA over denitrification, which decreased the biotic contribution to N 2 O formation. Our results suggest that chemodenitrification could be a significant contributor for N 2 O emissions in paddy soils via a complex network of biotic and abiotic processes involving C, Fe, and N biogeochemical cycling.

（论 链接：https://pubs.acs.org/doi/10.1021/acsearthspacechem.9b00296）