Research Interests

My approach to research has been to focus on a single system, mycorrhizal interactions, while applying a broad range of research tools (molecular, physiological, modelling) and working across multiple scales from individual plants to ecosystem level outcomes. Here I list three of the broad themes of my research at the individual, community and ecosystem scale. 

• Understanding mycorrhizal fungal diversity and its role in plant adaptation to the environment. One of the most exciting recent developments in biology is the recognition that plants (and animals) are not so much individuals, but rather entire ecosystems of bacteria, fungi, and microfauna. This new paradigm is revolutionizing our understanding of medicine, ecology, and adaptation of organisms to their environment. I contribute to this in my own research, by focusing on the communities of symbiotic mycorrhizal fungi associated with plant roots, the mechanisms supporting that diversity, and how these fungi influence both plants, both individually and in communities, and ecosystem outcomes.

Most of my earlier work in this area was around micro- and meso-scale descriptive studies of niche differentiation by ectomycorrhizal fungi along vertical and horizontal gradients (soil profiles and forest edges, respectively). While I have found strong evidence for small-scale niche differentiation, results at larger scales shows greater homogeneity than expected, particularly at the level of fungal genera. This raises intriguing questions about whether plants are actively maintaining fungal diversity as a mechanism for maximizing enzymatic nutrient uptake capabilities. I am presently expanding this work to arbuscular mycorrhizal associations, working with L. Martinez-Garcia, J. Tylianakis, S. Richardson, and D. Peltzer, studying plant-fungal interaction networks across a 120 000 year gradient of ecosystem development and retrogression, including strong soil nutrient gradients, at the Franz Josef glacier chronosequence.

• The role of soil feedbacks in structuring plant communities. I initiated this research during my doctoral work, examining the role of post-fire residual trees in facilitating forest regrowth by providing patches of mycorrhizal fungal inoculum for seedlings. Since then, I have continued this theme by examining how mycorrhizal interactions control patterns of forest establishment into grasslands in Minnesota and New Zealand, and the role of symbiotic interactions in invasive species establishment in novel environments. This research has application in restoration ecology, invasion ecology, and in carbon sequestration. My current priorities in this area are (1) integrating soil feedbacks with seed dispersal in spatially explicit models, and (2) better understanding of the role of soil feedbacks in plant invasions. A major part of this work is linking plant invasions to ecosystem services and limits. I see New Zealand as an ideal system to understand plant invasions. These invasions provide not only a strong applied context, but also an excellent experimental system for studying the role of mutualisms.

• The role of mycorrhiza in changing ecosystems. In some ways my largest scale research is also the simplest in concept, simply asking whether and how ecosystem level outcomes are affected by the mycorrhizal status (arbuscular versus ectomycorrhizal) of dominant vegetation. Ectomycorrhizal dominated forests around the globe tend to share the characteristics of having low plant diversity and an accumulation of soil organic material. Using phylogenetically constrained contrasts we have recently rejected the previously dominant hypothesis for these patterns, that ectomycorrhizal trees have low-nutrient leaves (New Phytologist).  An alternative hypothesis was that ectomycorrhizal trees might have different roles in weathering rock-derived nutrients (so called "rock-eating-fungi"). However, in current collaborative research (with N. Koele, J. Blum, G. Lovett, and M. McGlone) using an 18 000-year natural experiment, where slow post-glacial spread has resulted in adjacent arbuscular and ectomycorrhizal forests on similar parent material, we have found no evidence to support different roles in rock dissolution. Finally, we have been developing stoichiometric ecosystem models to explicitly test the third possibility: that ectomycorrhizal fungi fundamentally alter ecosystem organic nutrient cycles (Ecology Letters 2011).