Research in the laboratory focuses on the ecological and evolutionary consequences of interactions among species, including mutualism, parasitism, and competition. We use theory, lab and field experiments, and synthetic approaches to address research questions. Our empirical work focuses mostly on interactions between trees and diverse communities of symbiotic ectomycorrhizal fungi. You can find a list of our publications here.
Ongoing projects fall into two general categories:
Local ecology of species interactions and communities. These projects aim to understand the strength, mechanisms, and community-level consequences of interactions between species in plant and mycorrhizal fungal communities. Current projects and major foci include:
How do mycorrhizal fungi influence plant-plant interactions? With support from the National Science Foundation (DEB award # 1119865), we are investigating how belowground mycorrhizal networks between trees influence the strength of plant-plant interactions in forests. Results from a three-year field experiment showed that access to mycorrhizal networks substantially enhanced survival of Monterey pine (Pinus radiata) seedlings in coastal California (Booth and Hoeksema 2010). However, seedlings with access to mycorrhizal networks often host different ectomycorrhizal fungal species than those cut off from networks, and the latter fungal species are usually only found during the early successional stages of forest development. Currently, we are testing whether early-, late-, and multi-stage fungi differ in the terms of nutrient exchange with pine seedlings, and whether those exchange rates depend on abiotic context (light levels and soil characteristics). The broader goal of this project is to understand the consequences for plant community dynamics of variation in traits and functions of different mycorrhizal fungal taxa. These data may also allow tests of predictions from economic models of mutualisms (see below). Outreach associated with this project includes teaching local high school students about soil ecology, and helping the conduct an experiment on the importance of soil microbes for plants (see some photos here).
How do biotic and abiotic factors interact to influence species interactions and community assembly? A variety of different approaches are being used to address this question. A collaboration with more than 15 different investigators (co-led with Nancy Johnson at Northern Arizona University, James Umbanhowar at the University of North Carolina, and Jim Bever at Indiana University), which began as a working group at the National Center for Ecological Analysis and Synthesis (NCEAS), aims to synthesize theory and empirical research on plant-mycorrhizal interactions to understand how their outcomes vary in response to changing biotic and abiotic contexts (Johnson et al. 2006, Schwartz et al. 2006, Hoeksema et al. 2010). One product of this collaboration is the MycoDB database (Chaudhary et al. 2010), in which we have compiled the results of hundreds of experiments in which plants were inoculated with mycorrhizal fungi. The database is being used in a series of meta-analyses (Hoeksema et al. 2010), with the goal of better predicting the context-dependency of ecological outcomes in the mycorrhizal symbiosis. A new working group at the National Evolutionary Synthesis Center will resolve problems in applying model selection (using information criteria such as AIC) to mixed multi-factor meta-analysis, and will develop methods for incorporating plant and fungal phylogenies into meta-analysis of mycorrhizal interactions. Recently departed post-doc (and ongoing collaborator) Justine Karst has used meta-analysis (e.g., Karst et al. 2008), experiments (Karst et al. 2011), and analyses of observational datasets on ectomycorrhizal community structure, including a collaboration with Kitty Gehring at Northern Arizona University. Former graduate student Anjel Craig tested the impact of forest restoration treatments on the community structure of ectomycorrhizal fungi in the diverse upland forests of northern Mississippi.
- Do symbioses act like biological markets? We are using theory to generate explicit hypotheses regarding the relative importance of market forces in the dynamics and stability of potential mutualisms between host and symbiont species (e.g., Hoeksema & Schwartz 2003), including an ongoing collaboration with James Umbanhowar (University of North Carolina).
Mycorrhizal networking cylinder used in field experiments to estimate effects of mycorrhizal networks on plant-plant interactions
Example of graphical analysis of potential for benefit from resource-exchange mutualism using the comparative advantage market model
Evolution of species interactions and communities. These projects aim to understand the mechanisms and consequences of the evolution of species in response to each other and to their abiotic environment. Current projects include:
- What are the patterns and consequences of coevolution in diverse, widespread mutualisms? In collaboration with John Thompson (University of California, Santa Cruz), Deborah Rogers (University of California, Davis), and Jesus Vargas Hernandez (Colegio de Postgraduados, Mexico), we are examining genetic variability and patterns of local adaptation among the different species of ectomycorrhizal fungi associated with pines on the West Coast of North America (Hoeksema & Thompson 2007, Piculell et al. 2008, Hoeksema et al. 2009), including an ongoing project focusing on Monterey pine (Pinus radiata) in its native populations in California and Mexico.
- How do genetic correlations among complex traits influence coevolutionary adaptation? In collaboration with a diverse group of investigators including Dana Nelson (USDA Southern Institute of Forest Genetics), David Neale (University of California, Davis), and John Davis (University of Florida), we are using the interactions between pines of the southeastern US (loblolly pine (Pinus taeda), and longleaf pine (Pinus palustris)) and their ectomycorrhizal fungi to understand the genetic basis of mycorrhizal traits in plants, and the evolution of those traits in response to natural selection. Graduate student Bridget Piculell is studying how genetic correlations among loblolly pine traits, including mycorrhizal traits and other key traits such as disease resistance, may constrain or enhance coevolution between plants and their mutualistic and parasitic symbionts. Graduate student Nicole Hergott is studying how genetic variation in longleaf pine may influence ectomycorrhizal communities, with resulting consequences for ecosystem processes.
Expedition to Cedros Island, Mexico to collect seeds and soil (containing resistant propagules of ectomycorrhizal fungi) from native Monterey pine (Pinus radiata) forest.
Dana Nelson in a common garden of loblolly pine (Pinus taeda) clones near the USDA Southern Institute of Forest Genetics in Saucier, Mississippi.