Abstract: Energy-yielding processes in the N-cycle form important links with the global C-cycle. One example is demonstrated with the supply of nitrogen to soils, initially resulting in lowered CO₂ emissions. This well known effect has mostly been interpreted as hampered or delayed soil respiration. When added in surplus, however, nitrogen supply does not stabilize the minimum emissions initially obtained, but gradually results in increased CO₂ emissions. Specific inhibition of the CO₂ consuming process nitrification in soils, with surplus ammonium supply or with acetylene, mostly results in additional CO₂ emissions. The difference between this disclosed gross heterotrophic respiration (GHR) and the net CO₂ emission (NHR) is the result of a within-soil CO₂-sink. Soil respiration solely determined as CO₂ emitted as NHR (the common situation) therefore may lead to misinterpretations of the function of the soil system, especially in areas with high N-deposition. As a consequence, the interpreted’acclimation’ of the soil respiration response in a warmer world should be reconsidered. The concept of respiration inhibition by nitrogen supply may also be questioned. Disregard of these processes, including the indicated N-driven within-soil CO₂-sink, may prevent adequate measures counteracting climate change.

Key words: soil respiration, carbon sink, CO₂ emissions, temperature response, climate change, N-supply