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. Our lab has been particularly interested in identifying mechanisms that determine competitive outcomes. In addition, we have also been involved in a number of collaborative research projects. With Kabir Peay and Tom Bruns, we examined the role of root density in ectomycorrhizal fungal succession and how ectomycorrhizal fungi may affect plant edaphic specialization at Lambir Hills National Park in the tropical rainforests of Borneo (Malaysia). With Tom Horton and Randy Molina, we investigated the arbutoid mycorrhizal communities associated with Arbutus menziesii. This tree appears to play a key legacy role in the successional dynamics of mixed evergreen forests by promoting high mycorrhizal fungal diversity and host plant connectivity. With Roberto Garibay-Orijel, we examined the ectomycorrhizal communities associated with Alnus trees in central Mexico and are planning to collaborate with Melanie Roy, Monique Gardes, and Pierre-Arthur Moreau on additional work in the Alnus ectomycorrhizal system in France.
Research on Frankia bacteria
Frankia is a genus of actinomycete bacteria that associates with a wide range of host plants. In the Pacific Northwest (PNW), these bacteria commonly associate with Alnus trees. 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 genotypic diversity of Frankia associated with Alnus in the PNW, particularly in field settings. To address this gap, we have been characterizing variation in the nif H gene region in nodules collected from a range of Alnus forests in Oregon, Washington, Idaho, and Mexico. This work has involved field surveys as well as growth chambers experiments (see the lab publications page for results of this research). We also compared the genotypic diversity of Frankia in nodules collected from the canopies of A. rubra trees in Olympic National Park with those collected from adjacent ground areas. That project was done in collaboration with Nalini Nadkarni.
The most current research focus of the lab is studying the three-way interactions among ectomycorrhizal fungi, Frankia bacteria, and Alnus trees. This work is supported by the National Science Foundation and the M.J. Murdock Charitable Trust. A summary is provided below.
Despite their well-recognized significance, the factors determining mycorrhizal assemblage structure remain poorly understood. Host plant preference/specificity is one of the few factors that has consistently been shown to influence the composition and diversity of mycorrhizal assemblages. Patterns of host plant preference/specificity have been particularly well-documented for the ectomycorrhizal (EM) assemblages associated with Alnus host species. These EM assemblages have significantly lower species richness and greater host specificity that other EM assemblages. Although this pattern has been well established from observational, experimental, and molecular-based studies, the mechanism(s) determining the lower richness and higher proportion of host-specific species of Alnus EM assemblages are not clear. We hypothesize the unique composition of Alnus EM assemblages is driven by the co-presence of nitrogen-fixing Frankia bacteria. These bacteria strongly affect both the soil abiotic environment as well as the nutrient status of their shared host. To determine the role Frankia bacteria play in shaping Alnus EM assemblages, we have designed a series of field, lab, and culture-based experiments that utilize a range of molecular and biochemical analyses.
In addition to this work, we have a number of other projects on microbial ecology. Current collaborative projects include studying the effects of soil depth on ectomycorrhizal competition with Alija Mujic (OSU), Joey Spatafora (OSU), and Dan Durall (UBC), and exploring the genetic basis of spore type in Frankia nodules with John Markham (University of Manitoba). We welcome the opportunity to collaborate with other researchers as well.