Contribution of rhizomicrobial and root respiration to the CO2 emission from soil (A review)

Separate determination of root respiration and rhizomicrobial respiration is one of the most interesting, important, and methodologically complicated problems in the study of the carbon budget in soils and the subdivision of the CO2 emission from soils into separate fluxes. In this review, we compare the main principles, the advantages and disadvantages, and the results obtained by the methods of component integration, substrate-induced respiration, respiratory capacity, girdling, isotope dilution, model rhizodeposition, modeling of the 14CO2 efflux dynamics, exudates elution, and the δ13C measurements of the microbial biomass and CO2. Summarizing the results of the determinations performed by these methods, we argue that about 40% of the rhizosphere CO2 efflux is due to root respiration and about 60% of this efflux is due to the respiration of microorganisms decomposing root exudates.