Mn(III)-Driven Litter Decomposition Along Oxic-Anoxic Interfaces in Temperate Forest Soils.

Decomposition of plant detritus (litter) is a fundamental process regulating the release of nutrients for plant growth and the proportion of carbon that is lost to the atmosphere as CO₂. Recent evidence suggests that decomposition rates within forest soils depend on the amount of Mn(II) available to litter-decomposing fungi and their ability to produce reactive Mn(III) species. Many forest soils are characterized by steep oxygen gradients, forming oxic-anoxic transitions that enable rapid redox cycling of Mn. These oxic-anoxic interfaces have been shown to promote fungal Mn oxidation and frequently contribute disproportionally to CO₂ emissions from soils. Interestingly, ligand-stabilized soluble Mn(III), which ranks second only to superoxide as the most powerful oxidizing agent in the environment, has recently been found to preferentially form along oxic-anoxic transitions in sediments.

This study aimed to quantify fungal Mn(III) production along oxic-anoxic interfaces and in relation to litter decomposition within forest soils. To accomplish this goal, we investigated the sources and speciation of Mn in relation to fungal activity along redox interfaces in both a field and laboratory settings. We found that leaf litter, as opposed to mineral soil, is the largest source of bioavailable Mn. In the field, we observed the greatest oxidative enzyme activity and Mn(III) production along oxic-anoxic boundaries, coinciding with enhanced oxidation of litter. Additional reactor experiments revealed the formation of dense fungal networks along oxic-anoxic interfaces. Preliminary electrochemical, spectrophotometric, and X-ray spectromicroscopic analyses indicate that oxic-anoxic interfaces represent ideal niches for fungal Mn(III) formation. Our results suggest that that the litter-decomposing fungi rely on Mn redox cycling across oxic-anoxic interfaces to produce Mn(III) based oxidants. As predicted changes in the frequency and timing of drought and precipitation alter soil moisture regimes, understanding the mechanistic link between Mn cycling and litter decomposition along oxic-interface is becoming increasingly important.

---

See more from this Division: SSSA Division: Soil Chemistry
See more from this Session: Microbial Transformations of Minerals, Metals and Organic Matter I.: Impacts on Contaminant Dynamics and Carbon Storage Oral (includes student competition)

<< Previous Abstract | Next Abstract >>