I completed my Ph.D. in May of 2005 in the Department of Integrative Biology at the University of California, Berkeley. The title of my dissertation was “Ecological factors affecting forest encroachment into coastal California grasslands” and I was co-advised by Drs. Wayne Sousa and Thomas Bruns. Following graduation, I worked as a National Parks Ecological Research Fellow at the University of California, Berkeley and Point Reyes National Seashore. My post-doctoral supervisor was Dr. Thomas Bruns in the Department of Plant and Microbial Biology. I examined interspecific competition among ectomycorrhizal fungi and its effect on fungal assemblage structure and plant performance. Please see my curriculum vitae for additional details about my education, research, and teaching background.
In August of 2007, I began working at Lewis and Clark College in Portland OR as a Professor of Biology.
Identifying the factors that determine assemblage structure and diversity are fundamental questions in ecology. There traditionally has been a strong focus in plant ecology on aboveground processes such as seed dispersal, light competition, and herbivory. While these factors are clearly important, a growing number of studies indicate that interactions with belowground organisms may also have a large effect on plant assemblages. My research has examined the interactions between plants and mycorrhizal fungi. In this interaction, the fungi give plants nutrients and water in exchange for carbon. The plant-mycorrhizal symbiosis is extremely widespread and appears to have an important yet significantly understudied effect on plant interactions and community dynamics. A major reason why this symbiosis has not been studied by ecologists until recently is that identifying and manipulating the fungi was extremely difficult. However, a number of breakthroughs in molecular biology in the last ten years have made it possible to ask ecological questions about the role of mycorrhizal fungi in plant community dynamics. I am currently using these molecular tools, in combination with field and laboratory experiments, to address questions about plant-plant interactions and both plant and fungal community structure. The field of plant-mycorrhizal ecology is primed for further investigation and my current work is making an important contibution of this exciting new research field.
Although I have focused most of my research on the plant-mycorrhizal symbiosis, I have worked on a number of other topics including niche partitioning in forest understory establishment, seed dispersal and predation, and how seed reserves affect early seedling performance. With my Ph.D. co-adviser Wayne Sousa, I also have studied different aspects of mangrove ecology, including the spatial patterning of propagule dispersal and the effects of size and insect damage on seedling establishment. In my research, I have worked with a broad range of experimental settings, from microcosm bioassays to manipulative field experiments and tried whenever possible to pair greenhouse and field studies to provide maximum scientific inference. Similarly, I have used a number of different methodological approaches and have particularly strong experience in molecular and stable isotope methods as well as experimental design and statistical analyses. Below, I present the major findings from my research to date as well as directions I would like to pursue in the future.
I. Integrating mycorrhizal fungi into studies of plant-plant interactions
The same fungal individual can physically link plant individuals of the same and different species. Significant quantities of resources can also be passed between plants via these common mycorrhizal networks (CMNs), which may a large impact on plant ecology through facilitation of seedling establishment and mediation of competition. I examined this topic in a study of mycorrhizal fungi associated with Pseudotsuga menziesii and Lithocarpus densiflora. Typically Pseudotsuga dominates the canopy of mixed evergreen forests while Lithocarpus occurs mostly in the forest understory. Using a combination of restriction fragment length polymorphism (RFLP) and DNA sequencing to identify the fungi, I was able to show that there was a high potential for Pseudotsuga and Lithocarpus to be connected by CMNs in the field. While other studies had demonstrated that plants could be connected by CMNs in the field, my work was one of the first to show CMNs could occur between tree species that are distantly related phylogenetically. I also looked effects of fungi on the encroachment of these two species into grasslands. On Mount Tamalpais, there has been widespread encroachment of Pseudotsuga into the grasslands, with more limited encroachment of Lithocarpus. Interestingly, Lithocarpus individuals are only found under Pseudotsuga individuals in the grassland. I found that the dominant fungi in the grasslands are host-specific to Pseudotsuga, but under established Pseudotsuga individuals, there were fungi that also associated with Lithocarpus. These data suggest mycorrhizal fungi may play an important role in the patterning and rate of encroachment of the two species into the grasslands.
While I believe that mycorrhizal fungi play an important role in shaping plant distributions, particularly at the seedling stage, I realize that there are many factors affecting their distribution and abundance. In the Mt. Tamalpais system, I also investigated the simultaneous effects of competition and facilitation from previously established Pseudotsuga individuals on Pseudotsuga and Lithocarpus seedling establishment. I found that larger Pseudotsuga individuals had strong net positive effects on the seedling establishment of both species. The facilitation appeared to be largely driven by fog water collection, which ameliorated soil moisture conditions during the dry summer months. To ascertain this effect, I simulated the presence of Pseudotsuga saplings using artificial plastic trees, which allowed me to separate the biotic and abiotic effects of the saplings on seedling establishment. In my future research, I plan to continue to take a multi-faceted experimental approach such as the one I used in my dissertation to simultaneously test how mycorrhizal fungi and other ecological factors influence plant interactions and distributions.
- Kennedy, P. G. and Sousa, W. P. 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., 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.
II. Exploring the effects of plant-fungal feedbacks on fungal competition
For my post-doctoral research, I am focusing on interspecific competition among ectomycorrhizal fungi and its effects on fungal assemblage structure and plant performance. Competition among fungi is a particularly important topic in plant ecology because mycorrhizal fungi differ considerably in their abilities to take up nutrients and withstand water stress. Thus, plants associated with different fungi may differ in competitive abilities as well as tolerances to environmental stress. I am exploring this topic with species in the genus Rhizopogon, which can be easily manipulated in field and laboratory experiments. I am using the host plant Pinus muricata, which forms mono-dominant stands along parts of the California coast. The specific topics I am studying include how colonization timing affects competitive dynamics, whether competitive hierarchies are present among fungi, and whether competition occurs directly among the fungi or is indirectly mediated by the plants. To assess the outcome of fungal competition, I am using real-time PCR, in which I have designed and optimized species-specific primers and fluorescently labeled probes.
- Kennedy, P. G., Bergemann, S. E., Hortal, S., and T. D. Bruns. 2007. Determining the outcome of field-based competition between two Rhizopogon species using real-time PCR. Molecular Ecology 16(4): 881-890. doi: 10.1111/j.1365-294X.2006.03191.x.
- 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.
III. Environmental context-dependence in the mycorrhizal symbiosis
The mycorrhizal symbiosis is a trading system in which both symbionts exchange resources. Typically the symbiosis is framed in terms of nutrient dynamics, with plants providing sugars to the fungi in exchange for nutrients, such as nitrogen and/or phosphorus. While this exchange is typically considered to be mutually beneficial, the trading environment may have a large impact on the outcome of the symbiosis. For example, in high nutrient settings, mycorrhizal colonization usually decreases, presumably because plants can acquire sufficient nutrients on their own. I have recently been working on a project examining how different soil moisture conditions affect the outcome of the mycorrhizal symbiosis. In collaboration with Kabir Peay, a graduate student at University of California, Berkeley, I found that the growth of both the plants and the fungi was significantly limited under very low soil moisture conditions. This had important consequences for the efficacy of the symbiosis, as mycorrhizal plants performed no better than non-mycorrhizal plants in these conditions. In higher soil moisture conditions, however, mycorrhizal plants performed significantly better in terms of growth, photosynthetic and conductance rates, and nutrient status compared to non-mycorrhizal plants. Our data suggest that the effects of mycorrhizal fungi on plant performance are likely to be context-dependent and that fluctuating environmental conditions may strongly affect the nature of plant-mycorrhizal interactions.
- Kennedy, P. G. and K. G. Peay. 2007. Different soil moisture conditions change the outcome of the ectomycorrhizal symbiosis between Rhizopogon species and Pinus muricata. Plant and Soil 291: 155165. doi 10.1007/s11104-006-9183-3.
Other Selected Publications:
- Peay, K. G., P. G. Kennedy, and T. D. Bruns. 2011. Rethinking ectomycorrhizal succession: are root density and hyphal exploration types drivers of spatial and temporal zonation? Fungal ecology 4: 233-240. [supplimental data]
- Peter G. Kennedy, Kabir G. Peay and Thomas D. Bruns. 2009. Root tip competition among ectomycorrhizal fungi: Are priority effects a rule or an exception? Ecology 90(8): 2098 2107.
- Kabir G. Peay, Peter G. Kennedy and Thomas D. Bruns. 2008. Fungal community ecology: a hybrid beast with a molecular master. BioScience 58(9): 799-810.
- Peter Kennedy and Tom Bruns. 2007. Mycorrhizas take root at the Ecological Society of America. New Phytologist 176(4): 745748. doi:10.1111/j.1469-8137.2007.02280.x
- Peter G. Kennedy, Sarah Hortal, Sara E. Bergemann and and Thomas D. Bruns. 2007. Competitive interactions among three ectomycorrhizal fungi and their relation to host plant performance. Journal of Ecology 95: 13381345.
- Kabir G. Peay, Thomas D. Bruns, Peter G. Kennedy, Sarah E. Bergemann and Matteo Garbelotto. 2007. A strong speciesarea relationship for eukaryotic soil microbes: island size matters for ectomycorrhizal fungi. Ecology Letters 10: 470480. doi: 10.1111/j.1461-0248.2007.01035.x.
- T. A. Rusca, P. G. Kennedy and 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(3): 551-560.
- P. G. Kennedy, N. J. Hausmann, E. H. Wenk, T. E. Dawson. 2004. The importance of seed reserves for seedling performance: an integrated approach using morphological, physiological, and stable isotope techniques. Oecologia 141: 547554.