Soil respiration (soil CO2 efflux) originates from autotrophic root respiration and heterotrophic microbial respiration in the bulk soil and in the rhizosphere. Since soil respiration is one of the major fluxes in terrestrial ecosystems, small changes in the magnitude of this flux could have large effects on the concentration of CO2 in the atmosphere. However, processes in the soil are highly complex and many aspects are still poorly understood. Therefore, detailed studies on soil respiration and related parameters were carried out in a highly heterogeneous unmanaged deciduous forest in the National Park Hainich (western Thuringia, Germany) and in an elevated CO2 experiment in an agricultural field close to Braunschweig, Germany.