Iron sulfide plaques have been observed on roots of wild rice (Zizania palustris) and other wetland plants grown in sulfur-impacted freshwater ecosystems, but the mechanism of their formation and ramifications for plants have not been investigated. We exposed a model annual wetland plant, Zizania palustris, to elevated sulfate concentrations (3.1 mM) and quantified the development of iron oxide and iron sulfide precipitates on root surfaces throughout the plant life cycle. During the onset of seed production, root surfaces amended with sulfate transitioned within 1 week from iron (hydr)oxide plaques to iron sulfide plaques. During the same week, Fe(III) decreased on roots of plants not amended with sulfate but FeS did not accumulate. Prior to FeS accumulation, sulfate-amended plants had taken up the same amount of N as unamended plants. After FeS accumulation, total plant nitrogen did not increase further on sulfate-amended plants, indicating a cessation in nitrogen uptake, whereas total plant N continued to increase in unamended plants. Sulfate-amended plants produced fewer and lighter seeds with less nitrogen than unamended plants. FeS precipitation on roots may be associated with elevated sulfide and inhibited nitrogen uptake before the end of the plant’s life cycle, thus affecting the populations of this annual aquatic plant. We propose a mechanism by which a physiologically-induced decline in radial oxygen loss near the end of a plant’s life cycle initiates a precipitous decline in redox potential at the root surface and in adjacent porewater, initiating accumulation of iron sulfide plaques. These plaques could be an important locus for iron sulfide accumulation in wetland sediments.
Bibliographical noteFunding Information:
Acknowledgements This research was funded by Minnesota Sea Grant and Fond du Lac Band of Lake Superior Chippewa. Sediment was provided from a wild rice lake on the Fond du Lac Reservation.
© 2018, Springer Nature Switzerland AG.
- Electron accepting buffer
- Iron–sulfur cycling
- Radial oxygen loss
- Root plaques
- Zizania palustris
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Wild rice geochemistry and reproductive life stage data from experimental pots amended with sulfate, 2016
LaFond-Hudson, S., Johnson, N. W., Pastor, J. J. & Dewey, B., Data Repository for the University of Minnesota, 2019