Microbial communities and soil carbon (C) have been shown to vary in response to increasing vegetation cover during soil development after deglaciation. However, little is known about the ability of microorganisms to utilize various C sources in glacier forefield soils. We supplied ecologically relevant ¹³C-labeled C sources (Chlorella, Penicillium and Festuca) to three distinct environments (supraglacial sediments, barren soils and vegetated soils) of the Damma glacier area to monitor ¹³CO₂ production. We identified prokaryotic and fungal populations able to utilize these sources by using DNA-stable isotope probing coupled with Illumina MiSeq sequencing of ribosomal markers. A high initial ¹³CO₂ pulse indicated that ¹³C-labeled microbial and plant material were consumed. The ¹³C-enriched DNA results indicated that betaproteobacterial taxa affiliated to the families Oxalobacteraceae and Comamonadaceae were important players in C utilization from different sources and present in all environments. In contrast, different fungal taxa played different roles in C degradation depending on the soil environment. Overall, our findings reveal that C utilization is driven by similar prokaryotic populations along a glacier forefield, while the distribution of active fungal populations are more influenced by environmental factors.