Studies on how microbes use C in soils typically assume oxic conditions but often overlook anaerobic processes and extracellular metabolite release. We examined how O₂ and Fe content affect C mineralisation in forest soils by tracking ¹³C flow into biomass, CO₂, metabolites, and active microbes under oxic and anoxic conditions. Results showed that anoxic conditions preserved C longer, especially in high-Fe soils. We conclude that microbial exudates play a role in anoxic C stabilisation.