I want to compare the recalcitrance of two different root residues by incubation to infer differences in potential SOC sequestration. Many studies do this by showing the short-term CO2 efflux; however, this says nothing about the stable fraction or potential sequestration. A sample with faster short-term decay may have a longer MRT for its stable fraction. Why not measure TOC at time points over a longer incubation instead of CO2?
CO2 efflux (if measured correctly, e.g. by using IR gas analyzers) is one of the best non-destructive technique. It allows to monitor decomposition over long time period including stages of slow decomposition of the most resistant components of plant residues. Single short-term CO2 efflux is meaningless for decomposition/sequestration studies, I agree with Justin. However switching to any other alternative single-term analysis is also bad idea. Use a combination of techniques over time and be prepare to spent months if not years to characterize recalcitrant plant constituents. TOC alone is not adequate because plant decomposition (TOC decrease) is accompanied with growth of decomposers (microbial biomass adds TOC), therefore you measure the difference underestimating decomposition rate and overestimating sequestration. You need to go to specific fractions like lignin, cellulose, hemicellulose, proteins, specific microbial polymers (e.g. peptidoglycans) etc. Thousands of papers published on the subject, the best modern method is NMR and mass-spectrometry but they are expensive.
Thanks so much Nicolai. I do plan to use a combination of TOC (Leco) and solid state NMR taken every 2 weeks for 2 years. I will homogenize/mill the entire soil conical before sampling (its unnatural, but the only way). Thanks for your answer!!