Research in the laboratory focuses on the ecological and evolutionary consequences of interactions among species, including mutualism, parasitism, and competition. We use lab experiments, field studies, modeling, and meta-analysis 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 under several broad questions:

How do ecological context and evolutionary history influence the outcomes of species interactions?

  • To address this question, we are using phylogenetic meta-analysis of a large database of experiments measuring plant growth responses to mycorrhizal fungi. This work has been conducted as part of a long-standing collaboration with numerous individuals (read about the history of this collaboration here). One product of this collaboration is the MycoDB database (Chaudhary et al. 2010, 2016), 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, Rúa et al. 2016 & 2018, Hoeksema et al. 2018), with the goal of better predicting ecological outcomes in the mycorrhizal symbiosis. Our most recent analyses suggest an important role for evolutionary history in predicting cotemporary outcomes of mycorrhizal interactions. Ongoing work will aim to better characterize that evolutionary history, including the potential role of natural selection, and to more deeply model the influences of important contextual factors like light and soil nutrient availability, so that we can understand the balance between ecological context and evolutionary history.

Fig1 from Hoeksema et al 2018

Figure 1 from Hoeksema et al. 2018, illustrating the effect of plant and fungal phylogeny on the average magnitude of plant growth response to mycorrhizal fungi.

 

What are the community, ecosystem, and evolutionary consequences of coupled plant-fungal invasions?

  • As human activities increasingly alter the relative dominance and distributions of biotic communities through introductions and management, major geographical shifts are occurring in plants and plant-associated soil microbial communities, resulting in new plant-microbe assemblages in exotic environments. These novel assemblages can provide exciting opportunities to answer integrative questions on the eco-evolutionary dynamics of biotic redistributions, and their consequences for biodiversity and ecosystem functions. For example, 300 years of pine introductions into the Southern Hemisphere have been accompanied by co-introduction of associated microbial communities, particularly obligate symbiotic ectomycorrhizal (EM) fungi, which thrive in exotic pine habitats but are much less diverse than in native pine habitats. Moreover, pines often invade into nearby habitats and are accompanied by an even less diverse, but still thriving, suite of co-invading exotic EM fungi. Both pines and EM fungi can have dramatic effects on biodiversity and ecosystem function, and the repeated introduction of different pine hosts and EM fungal symbionts into a diversity of exotic environments in the Southern Hemisphere can be viewed as an opportunity: a powerful natural experiment for asking how introduced host-symbiont assemblages affect community and ecosystem functions, and how members of diverse assemblages evolve across a geographic mosaic of abiotic and biotic environmental factors. We are pursuing these questions in collaboration with Steve Brewer, Rytas Vilgalys, Francois Teste, Laszlo Nagy, Sunny Liao, Jenny Talbot, Eddie Brzostek, and others.

pine-fungal invasion

How do mycorrhizal fungi influence plant-plant interactions?

  • 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 their nutrient exchange relationships with pine seedlings, and whether those exchange rates depend on abiotic context (e.g., ambient light levels). The broader goals of this project are to understand the consequences for plant community dynamics of variation in traits and functions of different mycorrhizal fungal taxa, and to test whether nutritional mutualisms function like biological markets (Schwartz & Hoeksema 1998, Hoeksema & Schwartz 2003). 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).cylinder
  • Mycorrhizal networking cylinder used in field experiments to estimate effects of mycorrhizal networks on plant-plant interactions


     

     

     



 

How do diverse mutualisms coevolve?

  • The geographic mosaic theory of coevolution predicts that geographically variable coevolutionary selection is important for trait diversification, but robust tests of this prediction are rare in diverse mutualisms. When there are numerous species on one or both sides of an interaction, does coevolution still drive trait evolution, or is selection from abiotic sources more important? One set of projects addressing this question is focused on estimating genetic variability and trait diversification in interactions between diverse communities of ectomycorrhizal fungi and pines (Hoeksema & Thompson 2007, Piculell et al. 2008, Hoeksema et al. 2009, Hoeksema et al. 2012).
  • On Cedros Island

     

    Expedition to Cedros Island, Mexico to collect seeds and soil (containing resistant propagules of ectomycorrhizal fungi) from native Monterey pine (Pinus radiata) forest.

     

     

    Bridget Piculell's PhD research, in collaboration with Dana Nelson (USDA), used the interactions between loblolly pine (Pinus taeda) and its ectomycorrhizal fungi to understand the genetic basis of "mycorrhizal traits" in plants including their heritability, underlying candidate genes, and how correlations with other pine traits such as disease resistance (Piculell et al. 2018) may influence responses to selection. Ongoing collaborative work with Megan Rua is directly estimating natural selection on traits of the interaction between Monterey pine (Pinus radiata) and its ectomycorrhizal fungi, using results from common garden experiments at field sites in coastal California.

    Dana in loblolly garden

     

    Dana Nelson in a common garden of loblolly pine (Pinus taeda) clones near the USDA Southern Institute of Forest Genetics in Saucier, Mississippi.