Implications of increased carbon dioxide levels for carbon input and turnover in soils

The complexity of the plant-soil system in its interaction with the changing climate is discussed. It is shown that processes at the level of organic matter inputs into the soil and the fluxes and pools involved in the global cycle are not known in sufficient detail to allow an estimation of the future quantitative shifts. Even the direction in which the level of stored carbon in the soil organic matter pool will develop is not clear. The importance of the nitrogen cycle, which is intimately coupled to the carbon cycle through the turnover of soil organic matter is underlined. In its turn, the mineralisation of soil organic matter takes place at a rate which is highly dependent on the nature of inputs and the availability of mineral nutrients.Aspects of shifts in temperature, changes in cultivation practices (reduced tillage) and unintended spreading of inputs in chemical N-fertilizers are of great importance at a regional and global scale.The complexity of the interactions in the process of mineralisation do require further studies to clarify the point whether a substantial and durable additional storage of carbon in soil organic matter is likely, or that shifts in temperature will cause an overriding acceleration of the mineralisation, and trigger a corresponding net release of carbon.