Microbial carbon use efficiency of glucose varies with soil clay content: A meta-analysis

Abstract

Soil organic matter (SOM) decomposition and stabilisation are largely affected by microbial carbon use efficiency (CUE), which is defined as the proportion of substrate carbon (C) uptake that microbes use for growth. Microbial CUE varies due to substrate quality and availability differences, but this may also depend on soil properties, such as pH, soil organic C (SOC) and clay content. We conducted a meta-analysis using data from 26 publications and analysed 272 CUE observations to investigate whether the substrate type has a distinct effect on microbial CUE and how CUE varies with the amount of substrate application and soil factors (pH, SOC, and clay content). We observed large variations in the CUE among different substrates, but we could not discern clear associations with substrate complexity, nitrogen, and energy content. Most of the studies used glucose as the substrate. The CUE of glucose significantly increased with decreasing amount of substrate applied and increasing clay content. We further observed a significant increase in glucose CUE with increased soil pH and decreased SOC content, although these relationships were relatively weak. Overall, our findings suggest the possibility of rapid adsorption of glucose or microbial products derived from glucose, which would then reduce substrate availability to microbes and increase CUE. The combined effects of greater adsorption and higher CUE with increased clay content would therefore result in more C stabilisation. We emphasise the need for including rapid adsorption of substrates and their microbial products when investigating substrate-specific microbial CUE.