ABSTRACT
This chapter presents the topics which concerns the metabolic uptake of oxygen and production of carbon dioxide by soil microbes and plant roots. Other biological processes as well as chemical reactions and the respiration of soil microfauna are omitted as being of minor importance for the oxygen and carbon dioxide budget in soil. For the soil air composition, undoubtedly, oxygen and carbon dioxide are of major importance. Oxygen is mainly consumed, in the process of respiration. However, it may also be produced, for example, by autotrophs assimilating carbon dioxide among which algae predominate. The molar ratio of carbon dioxide evolved to oxygen consumed is called the respiratory quotient (RQ). This quotient depends both on the substrate used and on the type of metabolism. The equation of Michaelis-Menten in the case of aerobic microorganisms describes both the oxygen uptake and the corresponding carbon dioxide production, as the RQ value is equal to 1.
