Separation of root and rhizomicrobial respiration by natural 13C abundance: Theoretical approach, advantages and difficulties

This contribution provides an elaboration of the theoretical background of an easy procedure allow- ing quantitative separate estimation of root respiration and rhizomicrobial respiration in nonsterile soils. The method is based on 13 C natural abundance by growing C 4 plants on C 3 soil or vice versa. Four δ 13 C values are necessary: of the soil organic matter, of the roots, of the soil microbial biomass, and of CO 2 efflux from the soil. The advantages and assumptions of the new approach, as well as possible applications including FACE systems and continuous labeling ( 13 C or 14 C) experiments are discussed. It is expected that the new method will become the standard procedure for separate estimation of root respiration (=respiration of autotroph organisms) and rhi- zomicrobial respiration (=respiration of heterotroph organisms) in nonsterile soils.