Theoretical background for partitioning of root and rhizomicrobial respiration by δ13C of microbial biomass

This contribution provides an elaboration of the theoretical background of a procedure allowing quantitative separate estimation of root respiration and rhizomicrobial respiration in non-sterile soils. The method is based on 13C natural abundance by growing C4 plant on C3 soil or vice versa. Four δ13C values are necessary: of the SOM, of the roots, of soil microbial biomass, and of CO2 efflux from the soil. The advantages and assumptions of the new approach, as well as possible applications including FACE systems and continuous labeling experiments are discussed.