Abstract
Background and aimsMineralization 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.MethodsWe incubated O-horizon soil samples (with either 13C–glucose or 13C–cellulose) from a boreal coniferous forest at 4, 9, 14, and 19 °C, and calculated CUEs based on the amount of 13C–CO2 and 13C–labelled microbial biomass produced. The effects of substrate, temperature, and metabolic conditions (representing unlimited substrate supply and substrate limitation) on CUE were evaluated.ResultsCUE 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 °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.ConclusionsWe 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.
Highlights
The world’s soils store very large quantities of carbon (3000 Pg; Tarnocai et al 2009) several times the amount of CO2-C in the atmosphere
The part of the CO2 soil flux originating from mineralization of soil organic matter (SOM) is controlled by microbial activity and how microorganisms partition the decomposition of OM between energy yielding processes associated with CO2 production and microbial biomass growth
This relationship between anabolic and catabolic activity is often represented in terms of carbon use efficiency (CUE), a measure of the proportion of the utilized carbon source that is converted into microbial biomass
Summary
The world’s soils store very large quantities of carbon (3000 Pg; Tarnocai et al 2009) several times the amount of CO2-C in the atmosphere. The part of the CO2 soil flux originating from mineralization of SOM is controlled by microbial activity and how microorganisms partition the decomposition of OM between energy yielding processes associated with CO2 production (catabolic processes) and microbial biomass growth (anabolic processes). This relationship between anabolic and catabolic activity is often represented in terms of carbon use efficiency (CUE), a measure of the proportion of the utilized carbon source that is converted into microbial biomass (del Giorgio and Cole 1998; Winzler and Baumberger 1938). CUE differed significantly with metabolic conditions, i.e. CUE was higher during unlimited growth conditions as compared to conditions with substrate limitation
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