Manganese translocation and concentration on Quercus cerris decomposing leaf and wood litter by an ascomycetous fungus: active process with ecosystem consequences?

Abstract

Decomposing fungi translocate Mn as demonstrated by the fact that Mn has been found to accumulate on decomposing leaves associated with individual fungal hyphae and forming insoluble Mn(III,IV) oxides that remain concentrated in diffuse patches. We studied here Mn translocation and precipitation by the saprophytic fungus Alternaria sp. strain FBL507 both on naturally decomposing oak leaves and in vitro experiments. Manganese was translocated and precipitated in beads and encrustations along the fungal hyphae. The combination of X-ray diffraction and SEM-EDS chemical data showed that the precipitates found on leaves were rhodochrosite (MnCO₃), birnessite ([Na, Ca, K]Mn₂O₄ × 1.5H₂O) and possibly Mn oxalate. The precipitates on wood were an amorphous Mn-O compound, probably MnO. Thus, Mn oxidation state in the precipitates spanned from 2 + to + 4, with + 3 and + 4 only in the birnessite on the leaves. In vitro experiments showed that Mn precipitates formed in living hyphae, suggesting the possibility that Mn precipitation is actively produced by the fungus. Such a possibility opens interesting questions regarding the role of readily available Mn in the activity of saprophytic fungi and other soil microorganisms, such as would result in a large involvement of Mn in the cycles of the major nutrient elements.

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