PARENT SESSION
Contributed Oral Session 89: Soil Ecology: Plant - Soil Relationships
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 524 B, Level 5, Palais des congrès de Montréal

Bacterial functional groups and soil carbon cycling.

Fierer, Noah^*,1, Bradford, Mark², Jackson, Robert¹, Colman, Ben³, Schimel, Joshua³, ¹ Duke University, Durham, NC² University of Georgia, Athens, GA³ University of California, Santa Barbara, CA

ABSTRACT- The concept of functional groups has been central to studying the role of community composition and ecosystem function. Evaluating the roles of different groups of microbes in soil C and N turnover has proven difficult; there are many species of heterotrophic bacteria, and it has been unclear how to differentiate soil bacteria into meaningful functional groups that can be used to evaluate population/process relationships. Most work in this area has used approaches that provide either community fingerprints or "species" level resolution. We analyzed bacterial communities at the phylum level by using a quantitative PCR approach. We examined whether the relative abundances of six major bacterial phyla (Acidobacteria, Bacteroidetes, Firmicutes, Actinobacteria, and the ,−Proteobacteria) can be related to soil properties, including C and N mineralization rates, in 85 soils collected from across North America. Our goal was to assess if these bacterial phyla constitute useful functional groups for future analyses of soil C and N dynamics. Net carbon (C) mineralization rate (an index of C availability), was positively correlated with -Proteobacteria and Bacteroidetes, but negatively correlated with Acidobacteria. This suggests that these phyla can be differentiated into copiotrophs and oligotrophs (or r- and K- strategists, respectively). We tested this hypothesis by amending soil cores from a specific site (Duke Forest, NC) with varying levels of sucrose over a 12-month period. As predicted, increasing C availability led to a decrease in the abundance of the oligotrophic Acidobacteria and an increase in the copiotrophic -Proteobacteria and Bacteroidetes. The copiotroph/oligotroph hypothesis is further supported by a meta-analysis of published soil clone libraries. Together these results suggest that phylum-level bacterial abundances are largely predictable and that certain bacterial phyla may play distinct roles in processing organic C sources of varying quantity or quality.

Key words: bacteria, soil, carbon, PCR