Soil organic matter distributions, reservoirs, and mineralization rates in tundra soils are important factors for understanding biogeochemical carbon cycling. This study focuses on spatial trends and environmental controls of soil carbon distribution and microbial soil respiration in 4 tundra vegetation communities in an arctic valley in NE-Greenland (74°N), including Dryas and Cassiope heaths, Salix snow bed, and fen vegetation. Measured total soil organic carbon in the upper 50 cm averaged (±SD) 11.0 ± 1.5 kg C m ^-2 with spatial variations strongly affected by vegetation, hydrology, and buried organic layers. Observed soil CO₂ concentrations and effluxes were simulated with a steady-state diffusion model using laboratory measured CO₂ productions as input. Simulated CO ₂ profiles and CO₂ effluxes (up to 3 μmol CO ₂ m^-2 s^-1) agreed with field observations and revealed the importance of both vegetation- and depth-specific CO₂ production and CO₂ diffusion for understanding the spatial variation in near-surface soil CO₂ gas dynamics. These results confirm that molecular diffusion dominates gas transport in the studied soils; but also that the complexity of CO₂ production/transport coupled to soil heterogeneity (in particular the litter layer) complicates the application of soil-diffusion models to estimate seasonal trends of soil gas effluxes.