Symbioses: Plant, Animal, and Microbe Interactions
Deslippe, Julie R. , Neufeld, Josh D. , Mohn, William W. , Grayston, Susan J. , Simard, Suzanne W. .
Stable-isotope probing of the mycorhizosphere of intact dwarf shrubs provides insight into carbon cycling in Low Arctic tundra.
Ecosystem carbon balance comprises the sum of net primary productivity and heterotrophic respiration. In Low Arctic soils, the presence of permafrost, short growing seasons, and frequently water-saturated conditions limit microbial decomposition. As a result, disproportionately large stores of organic matter have accumulated in these cold ecosystems. Arctic soils occupy only 13% of the Earth’s surface but account for 26% of its carbon. Plant carbon flux to the rhizosphere is a critical process that couples plant and microbial productivity in terrestrial ecosystems. Despite its importance, this flux is among the least understood aspects of the global carbon cycle. We used stable-isotope probing of phospholipid fatty acids (PLFA-SIP) and DNA (DNA-SIP) to examine the fate of root exudates from tundra plants in the field. We hypothesized that carbon acquisition patterns in the rhizosphere would be a function of mycorrhizal type, and we selected plant species based on their mycorrhizal strategies: Betula nana (ectomycorrhizal), Salix pulchra (ecto- and arbuscular mycorrhizal), and Ledum palustre (ericoid mycorrhizal). In July and August of 2006 and 2007, plants were pulse-labeled with 1.29-2.15 mM 13CO2. Rhizosphere samples were collected from five replicate plants per species after a chase period of 28 hours or seven days. The PLFA profiles revealed a similar pattern for all plant species, with fungi and Gram-negative bacterial biomarkers being most enriched. The patterns were most apparent in August, reflecting increasing allocation of carbon below-ground as plants senesce. DNA-SIP analysis of August 2007 samples revealed that a single bacterial phylotype dominated the acquisition of plant root exudates in the rhizospheres of all three plant species, although 13C enrichment was least apparent for DNA obtained from the rhizosphere of Ledum palustre. Sequencing the 16S rRNA gene from this phylotype will help identify this key player in the carbon cycle of this Low Arctic tundra ecosystem.
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1 - University of British Columbia, Forest Science, 3621-2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada
2 - University of Waterloo, Biology, 200 University Avenue, Waterloo, ON, N2L 3G1, Canada
3 - University of British Columbia, Microbiology and Immunology, 4501-2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
4 - University of British Columbia, Forest Sciences, 3006-2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada
5 - The University of British Columbia, Forest Sciences, 2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada
Stable Isotope Probing
Presentation Type: Oral Paper:Papers for Topics
Location: Blair A/Gage
Date: Tuesday, July 29th, 2008
Time: 10:30 AM