The effect of temperature and substrate quality on the carbon use efficiency of saprotrophic decomposition

Background and aims Mineralization of soil organic matter (SOM) constitutes a major carbon flux to the atmosphere. The carbon use efficiency (CUE) of the saprotrophic microorganisms mineralizing SOM is integral for soil carbon dynamics. Here we investigate how the CUE is affected by temperature, metabolic conditions, and the molecular complexity of the substrate.Methods We incubated O-horizon soil samples (with either C-13-glucose or C-13-cellulose) from a boreal coniferous forest at 4, 9, 14, and 19 A degrees C, and calculated CUEs based on the amount of C-13-CO2 and C-13-labelled microbial biomass produced. The effects of substrate, temperature, and metabolic conditions (representing unlimited substrate supply and substrate limitation) on CUE were evaluated.Results CUE from metabolizing glucose was higher as compared to cellulose. A slight decrease in CUE with increasing temperature was observed in glucose amended samples (but only in the range 9-19 A degrees C), but not in cellulose amended samples. CUE differed significantly with metabolic conditions, i.e. CUE was higher during unlimited growth conditions as compared to conditions with substrate limitation.Conclusions We conclude that it is integral to account for both differences in CUE during different metabolic phases, as well as complexity of substrate, when interpreting temperature dependence on CUE in incubation studies.