In this study we investigated the relationship between HFA and PE by measuring litter- and SOM-derived carbon (C) fluxes after the addition of fresh plant litter. We reciprocally incubated three 13C labelled litter types (maize, bent and beech) in soils from ecosystems where these litters are abundantly produced (e.g., arable sites, grasslands and forests), with and without the addition of mineral nitrogen (N).