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Open Access Publications from the University of California

Iron addition to soil specifically stabilized lignin

  • Author(s): Hall, SJ
  • Silver, WL
  • Timokhin, VI
  • Hammel, KE
  • et al.

© 2016 Elsevier Ltd. The importance of lignin as a recalcitrant constituent of soil organic matter (SOM) remains contested. Associations with iron (Fe) oxides have been proposed to specifically protect lignin from decomposition, but impacts of Fe-lignin interactions on mineralization rates remain unclear. Oxygen (O2) fluctuations characteristic of humid tropical soils drive reductive Fe dissolution and precipitation, facilitating multiple types of Fe-lignin interactions that could variably decompose or protect lignin. We tested impacts of Fe addition on13C methoxyl-labeled lignin mineralization in soils that were exposed to static or fluctuating O2. Iron addition suppressed lignin mineralization to 21% of controls, regardless of O2availability. However, Fe addition had no effect on soil CO2production, implying that Fe oxides specifically protected lignin methoxyls but not bulk SOM. Iron oxide-lignin interactions represent a specific mechanism for lignin stabilization, linking SOM biochemical composition to turnover via geochemistry.

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