Recent research suggested that iron oxidation may protect carbon from drought-accelerated decomposition in wetlands by promoting the sorption of lignin derivatives and decreasing phenolic oxidase activities. Here we examined whether this mechanism exists in organic-rich peatlands, which store over 30% of the world's soil carbon, by simulating drought and flooded conditions in peat soil with and without the addition of reduced iron. Our results suggest that iron does not protect carbon from decomposition in organic-rich peatlands, and in fact iron may exacerbate carbon decomposition via precipitation of phenolic compounds, which otherwise have been shown to inhibit microbial activity. In addition, scanning electron microscopy analyses of different types of peat soil from Minnesota to Peru showed evidence of iron-sulfide minerals (pyrite), indicating that some portion of the reduced iron in peatlands is effectively immobilized and therefore does not interact with the carbon cycle.
Wang, H., River, M., & Richardson, C. J. (2019). Does an ‘iron gate’ carbon preservation mechanism exist in organic–rich wetlands? Soil Biology and Biochemistry, 135, 48–50. https://doi.org/10.1016/j.soilbio.2019.04.011