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Total fine root mass in forests is estimated between 5 and 8 t. ha-1. These fine roots deliver the forest soils with large amounts of C throughout the whole rooting zone, as they die after 1 to 2 years, and, thus, supply the soils with C via their turnover. Extramatricular hyphae of the mycorrhizal fungi are comparable to tree fine roots. The hyphae are linked to the mycorrhizal fine roots, and act as primary C suppliers throughout the whole rooting zone. However, their lifespans are much shorter than that of fine roots, between weeks and months. Together with the fine roots, they deliver via their turnover between 1 and 3 tC. ha-1. yr-1. Soil organic matter SOM, in contrast to roots and fungal hyphae, have large C stocks in forest soils with up to 200 tC. ha-1, however, due to a relatively small turnover of 0.01 to 0.0005 yr-1, only small decreases of C occur, between 0.05 and 2 tC. ha-1. yr-1. It is the challenge of the future to be able to predict the changes of belowground C in forests soils under altered climatic conditions such as the conditions of global climate change. Thus, the understanding of the belowground turnover processes is an issue of highest priority and all efforts need to be done in order to improve its knowledge.