The release of CO₂ from soils, known as soil respiration, plays a major role in the global carbon cycle. However, the contributions of different soil depths or the sources of soil CO₂ have hardly been studied. We quantified the CO₂ production for different soil layers (up to 1.5 m) in three soil profiles for 2 years. We found that 90 % of CO₂ production occurs in the first 30 cm of the soil profile, and that the CO₂ originated from young carbon sources, as revealed by radiocarbon measurements.