Effects of manganese addition on carbon release from forest floor horizons

Lignin concentration in organic residues largely controls their decomposition. Mn2+ may well play a key role in ligninolysis because it is a cofactor of manganese peroxidase, an enzyme of the lignin-degrading system. This study aims to investigate the effects of Mn2+ addition on forest floor horizon decomposition during laboratory incubation. Therefore, we sampled two distinct forest floors from European beech (Fagus sylvatica L.) stands: a mor and a moder. Lignin and Mn concentrations in forest floor upper layer were significantly larger in moder than in mor. Three horizons from each forest floor were separately incubated with or without Mn2+ addition (250 mg Mn.kg dry matter(-1)) and the release of both CO2 and dissolved organic C was measured. The dissolved organic C release was not impacted by the Mn2+ addition, while a clear increase in CO2 release from specific horizons was observed. Our data suggest that the impact of the Mn2+ addition depends on (i) the forest floor type and on (ii) the organic matter decomposition stage.