Wednesday, November 7, 2007 - 10:10 AM
290-2
Microbial Metabolism and SOM Dynamics.
Serita Frey, University of New Hampshire, Dept. of Natural Resources, 215 James Hall, 56 College Road, Durham, NH 03824 and Johan Six, University of California-Davis, Davis, CA 95616.
The complexity of belowground processes has made accurate prediction and modeling of soil C cycling a challenge. Extensive research has been done to estimate belowground plant C allocation, root growth and turnover, soil organic matter pool sizes, and the relative contribution of autotrophic versus heterotrophic respiration. One aspect that has been overlooked is microbial C utilization efficiency which determines the partitioning of substrate C between microbial biomass and CO2 production. This is one of the first processes determining the fate of new C inputs to soil, and as such, demands greater attention. In this presentation, we will discuss the ecosystem significance of accurately measuring microbial efficiency, summarize existing data, and examine the drawbacks of existing methods, as well as the environmental factors thought to control this aspect of microbial metabolism. We will also discuss several widely held assumptions that have not been validated. For example, it has long been assumed that fungi are more efficient than bacteria and as an extension, that fungal-dominated communities have a higher C utilization efficiency than bacterial-dominated soil communities. We will show that this assumption is not well supported by available data. Microbial C utilization efficiency is an important control on C cycling, but has not been well quantified for soils. The factors controlling this parameter are not well understood and this has led to some incorrect assumptions.