Welcome to the Kennedy lab!

Research interests

Research on determinants of plant assemblage structure and diversity has traditionally focused on aboveground factors such as seed dispersal, light competition, and interactions with herbivores. While these factors are clearly important, a growing number of studies indicate that interactions with belowground microorganisms also have a large effect on plant assemblages. Our lab studies microorganisms that provide plants with different resources in exchange for carbon derived from photosynthesis. Although these symbioses are very common, their ecological roles have only recently begun to be more fully understood. This is largely because breakthroughs in molecular biology have made it possible to ask more specific questions about these symbionts and their role in plant assemblage dynamics. We use molecular tools, in combination with field and laboratory experiments, to address a broad range of research questions.

Current research

We are investigating two types of plant-microbe symbioses. The first involves ectomycorrhizal fungi and the second involves actinorhizal bacteria.

This is a root of Alnus rubra, red alder. On top is a large nodule formed by Frankia bacteria. On the bottom are root tips colonized by unindentified ectomycorrhizal fungi. Both of these symbioses play a key role in plant nutrient status.

Research on ectomycorrhizal fungi

A major part of the research in this lab focuses on interspecific competition among ectomycorrhizal fungi and its effects on fungal assemblage structure and plant performance. This area of fungal ecology is expanding rapidly and there are many exciting new research directions. This lab has been particularly interested in identifying the mechanisms that determine competitive outcomes. Current projects include examining how timing of colonization affects competitive dynamics, how competitive outcomes may vary based on spore versus mycelial colonization, and how root density and mycelial foraging strategy interact to determine competitive outcomes. This research is currently funded by the National Science Foundation in collaboration with Dr. Tom Bruns and Kabir Peay .

Our lab is also examining ectomycorrhizal assemblages associated with A. rubra. Previous non-molecular research has shown that A. rubra appear to be colonized by a unique suite of ectomycorrhizal fungi and our lab is using a range of molecular tools to assess the composition and diversity of these assemblages in different Oregon A. rubra forests.

Research on Frankia bacteria

Frankia is a genus of actinomycete bacteria that associates with a wide range of host plants. In the Pacific Northwest, these bacteria commonly associate with A. rubra. Frankia play a significant role in ecosystem nutrient cycling by converting atmospheric nitrogen into ammonia (via N fixation). While the functional role of this symbiosis has long been recognized, little is known about the strain diversity of Frankia associated with A. rubra, particularly in field settings. We are currently investigating this diversity by characterizing variation in the nif and 16s gene regions in nodules collected from a range of alder forests in Oregon that vary in age and management regime. This project is being done in collaboration with Andrew Blume and Dave Hibbs at the Hardwood Silvicultural Cooperative . We are also comparing the strain diversity of Frankia in nodules collected from the canopies of A. rubra trees in Olympic National Park with those collected from adjacent ground areas. This project is being done in collaboration with Dr. Nalini Nadkarni at The Evergreen State College.

Click here to see images from our canopy sampling trip

Selected publications

Ectomycorrhizal competition

Kennedy P. G., S. Hortal, S. Bergemann and T. D. Bruns. 2007. Competitive interactions among three ectomycorrhizal fungi and their relation to host plant performance. Journal of Ecology 95: 1138-1345.

Kennedy P. G., S. Bergemann, S. Hortal and T. D. Bruns. 2007. Determining the outcome of field-based competition between two Rhizopogon species using real-time PCR. Molecular Ecology 16: 881-890.

Kennedy P. G. and T. D. Bruns. 2005. Priority effects determine the outcome of ectomycorrhizal competition between two Rhizopogon species colonizing Pinus muricata seedlings. New Phytologist 166: 631-638.

Ectomycorrhizal ecology

Kennedy P. G. and T.D. Bruns. 2007. Mycorrhizas take root the Ecological Society of America. New Phytologist 176: 745-748.

Kennedy P. G. and K. G. Peay. 2007. Varying soil moisture conditions change outcome of Rhizopogon species effects on Pinus muricata performance. Plant and Soil 291:155-165.

Peay K. P., T. D. Bruns, P. G. Kennedy, S. Bergemann, M. Garbelotto. 2007. A strong species-area relationship for eukaryotic soil microbes: island size matters for ectomycorrhizal fungi. Ecology Letters 10:470-480.

Rusca, T. A., P. G. Kennedy, T. D. Bruns. 2006. The effect of different pine hosts on the sampling of Rhizopogon spore banks in five Eastern Sierra Nevada forests. New Phytologist 170:15-160.

Kennedy P. G., A. D. Izzo, and T. D. Bruns. 2003. High potential for common mycorrhizal networks between understory and canopy trees in a mixed evergreen forest. Journal of Ecology 91: 1071-1080.

Plant ecology

Sousa W. P., P. G. Kennedy, and B. J. Mitchell 2007. Supply-side ecology in mangroves: do propagule dispersal and seedling establishment explain forest structure? Ecological Monographs 77: 53-76.

Palomino M., P. G. Kennedy, E. L. Simms 2007. Nickel hyperaccumulation as an anti-herbivore: considering the role of tolerance to damage. Plant and Soil 293: 189-195.

Kennedy P. G. and W. P. Sousa 2006. Forest encroachment into a Californian grassland: examining the simultaneous effects of facilitation and competition on tree seedling recruitment. Oecologia 148: 464-474.

Kennedy P. G., N. J. Hausmann, E. H. Wenk, and T. E. Dawson. 2004. The importance of seed reserves for early seedling performance: an integrative approach using morphological, physiological, and isotopic techniques. Oecologia 141: 547-554.

Kennedy P. G. and T. Quinn. 2001. Understory plant establishment on old-growth stumps and the forest floor in western Washington. Forest Ecology and Management 154: 193-200.

C.V.

Handy lab resources

• Bruns Lab at UC Berkeley
• Ecological Society of America
• International Canopy Network
• Mycological Society of America
• NCBI GenBank
• Oregon Mycological Society
• Portland Timbers