Different organic compounds have distinct residence times in soil and are degraded by specific taxaof saprotrophic fungi. It hence follows that specific fungal taxa should respire carbon of different agesfrom these compounds to the atmosphere. Here, we test whether this is the case by radiocarbon (14C)dating CO2 evolved from two gamma radiation-sterilised maritime Antarctic soils inoculated with puresingle cultures of four fungi. We show that a member of the Helotiales, which accounted for 41–56% ofall fungal sequences in the two soils, respired soil carbon that was aged up to 1,200 years BP and whichwas 350–400 years older than that respired by the other three taxa. Analyses of the enzyme profile ofthe Helotialean fungus and the fluxes and δ13C values of CO2 that it evolved suggested that its releaseof old carbon from soil was associated with efficient cellulose decomposition. Our findings supportsuggestions that increases in the ages of carbon respired from warmed soils may be caused by changesto the abundances or activities of discrete taxa of microbes, and indicate that the loss of old carbonfrom soils is driven by specific fungal taxa.