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Abstract Detail


MSA - Ecology/Pathology

McFarland, Jack M. [1], Taylor, Lee [2], Ruess, Roger [3], Olson, Karl [3], Knut, Kielland [3].

Changes in community composition of ectomycorrhizal fungi associated with Alnus tenuifolia in response to changing plant N:P balance.

Nitrogen (N) fixation by Alnus represents an essential component of the N cycle in boreal forest ecosystems. This is particularly true along floodplain chronosequences where up to 70% of the N accumulated during forest succession derives from fixation by A. tenuifolia. However, biological N fixation is energetically expensive, resulting in a high demand for phosphorus (P). Although ectomycorrhizal fungi (EMF) are adept at mobilizing recalcitrant P sources, they vary widely in their physiological capacities. Plants should select associations that balance carbon expenditure in supporting a mycobiont against the mineral nutrition derived from the fungal partner. The goal of our project was to determine if changes in plant N:P balance result in a corresponding shift in community composition of mycorrhizal fungi associated with A. tenuifolia. We analyzed fungal ITS rDNA sequences isolated from alder root tips (n = 864) collected from each of three mid-successional balsam poplar (Populus balsamifera) stands amended with either N or P. In agreement with published accounts of narrow mycorrhizal specificity in alder, we found fewer than 100 fungal OTUs. Though in most plots alder roots were dominated by only a dozen or so species, these fungi belonged to diverse lineages, e.g. Thelephoraceae, Pyronemataceae, and Helotiaceae. Using ordination analysis and MRPP tests of differences among treatments, we determined that alder-associated EMF community composition was indistinguishable between control and N-amended plots; however, stands fertilized with P demonstrated a marginally significant shift in community composition. More importantly, we observed a 33% reduction in EMF infection on fine roots collected from P plots. These results suggest that changes in P, but not N availability result in subsequent shifts to EMF community composition presumably as plants selectively down regulate carbon allocation to fungal partners in response to changing plant N:P balance.


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1 - University of Alaska Fairbanks, Institute of Arctic Biology, 311 Irving I, 902 N Koyukuk Drive, PO Box 757000, Fairbanks, AK, 99775-7000, USA
2 - University of Alaska Fairbanks, Institute of Arctic Biology, 311 Irving 1, Fairbanks, AK, 99775, USA
3 - University of Alaska, Institute of Arctic Biology, 311 Irving I Building, Fairbanks, AK, 99775, USA

Keywords:
alder
Ectomycorrhizae
nitrogen fixation
phosphorus
N:P
boreal forest.

Presentation Type: Oral Paper:Papers for Topics
Session: 18
Location: Cottonwood A/Snowbird Center
Date: Monday, July 27th, 2009
Time: 10:30 AM
Number: 18002
Abstract ID:923


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