Biochemistry and ecology of carbon use efficiency in soil ecosystems
CUE is defined as the amount of microbial biomass produced relative to the amount of substrate consumed (mol C per mol C). Narrowly defined, this is an ecophysiological variable influenced by the interaction between environmental conditions, substrate availability and type, and metabolic processes in living microbial organisms. More broadly defined, this is an ecosystem variable that defines the partitioning of a cohort of C going into the system and leaving the system. Time is not part of this definition, but it has a great influence on it: from a C-cohort perspective, in the long-term all CUE equals zero. Although we tend to associate the narrow definition with short-term and the broader definition with long-term processes, all processes of biochemistry and ecology in soil microbial communities happen continuously and simultaneously. The increasing importance of new technologies such as metagenomics, metatranscriptomics, metaproteomics, and metabolomics requires an increased understanding of C processing at the cellular scale. In this talk I will take a biochemical perspective on how CUE and its underlying processes change in response to C availability and temperature.
I will demonstrate that CUE and underlying metabolic processes are not influenced much by temperature and substrate availability using position-specific 13C-labeled tracers, and discuss the relative importance of time, biochemistry, and ecology in soil C cycling processes. I will also discuss some of the complexities our approach is faced with, including microbial community diversity, biochemical diversity, spatial and substrate diversity, and report results from attempts to test these assumptions. Finally, I will describe new attempts to determine metabolic process rates, growth, turnover, and CUE for individual microbial taxa in an intact soil microbial community.