What's on the menu? Assessing microbial carbon sources and cycling in soils using natural abundance radiocarbon analysis
Abstract
Organic matter in soils is composed of diverse materials in various stages of decomposition. Soil organic matter is not in a single pool but rather in multiple carbon pools with different intrinsic turnover times that can be on annual to decadal and even millennial timescales. Microorganisms can influence the total amount of carbon stored in soils and the turnover rates of these different pools. However, the links between microbes and their ability to utilize these various carbon pools are not well understood. Moreover, microbes have been shown to co-utilize a number of available carbon sources rather than a single carbon source under soil conditions which creates difficulties in identifying microbial carbon sources in the natural environment. Compound-specific radiocarbon analysis of microbial phospholipid fatty acids (PLFA) has become a useful tool in elucidating microbial carbon sources in complex environments with multiple carbon sources. We investigated microbial carbon cycling at an industrial site in Ontario which included a variety of carbon sources including vegetation, PAHs and natural organic matter (NOM). Using this approach, the 14C content of microbial membrane lipids (which reflects their carbon source) can be compared to surrounding carbon sources in order to assess which carbon source they are metabolizing and incorporating into their lipids. In addition, we assessed microbial community structure and diversity by analyzing amplified bacterial, eukaryotic and archaeal rDNA fragments with denaturing gel gradient electrophoresis (DGGE). The Δ14C value for PLFAs ranged from +54 to -697% which indicates that microbial carbon sources across soils differ. The Δ14CPLFA for some soils is consistent with modern carbon sources while Δ14CPLFA for other soils is consistent with natural organic matter including older pools of carbon. The microbial communities at this site are not metabolizing PAHs but rather they are utilizing various pools of natural organic matter as a carbon source. Moreover, our radiocarbon analysis of total organic carbon (TOC) and non-solvent extracted residue (representative of NOM) support the notion that soil organic matter is not homogenous and is comprised of multiple carbon fractions with different intrinsic turnover times. DNA fingerprinting revealed consistent levels of diversity across soils with the greatest diversity observed in the bacteria, followed by eukarya and finally archaea which had the lowest observed diversity. It was previously thought that there is a pool of refractory organic compounds that are biologically inert in soil however our findings indicate that microbes are able to utilize almost all available carbon sources in soil. These finding brings forth questions regarding the influence of microbes on soil organic matter stabilization and the bioavailability of different carbon pools.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B24A..01M
- Keywords:
-
- 0418 BIOGEOSCIENCES / Bioremediation;
- 0428 BIOGEOSCIENCES / Carbon cycling;
- 0465 BIOGEOSCIENCES / Microbiology: ecology;
- physiology and genomics