Verwertung organischer Substanzen durch mikrobielle Bodenbiomasse als eine Funktion chemisch-thermodynamischer Parameter

Carbon use efficiency of organic substances by soil microbial biomass as a function of chemical and thermodynamical parameters A simple calculation determining carbon use efficiency by soil microorganisms based on chemical and thermodynamical parameters of organic matter is proposed. The use efficiency characterizes carbon fraction of organic matter which is incorporated into the cells of the soil microbial biomass. The proposed approach is based on the transition of the organic matter enthalpy into the microbial biomass enthalpy considering the formation enthalpy of the end products of respiration like CO₂, NH₄⁺ and H₂O. The combustion energy content of organic matter was used for the calculations. This combustion energy content can be determined by simple analytical means. It can be derived from data given in the literature and for various agricultural products. The comparison of organic matter use efficiency data calculated as shown above with literature data produced by diverse methods showed a satisfactory correlation. The calculated enthalpy of formation and maintenance of a C-unit of soil microbial biomass under in situ conditions amounted to —153,3 kJ · gC^—1. This value is compared with the maintenance coefficient used in microbiology. The use of the suggested approach for the calculation of carbon use efficiency based on the substance composition of the organic matter allows a uniform, standardized procedure which is not dependent on specific experimental conditions.