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The role of resource mutualisms in plant adaptation to abiotic environments


Hog peanut roots with nodules

Heterogeneous environments can drive differential selection on populations, leading to local adaptation. Although there are ample demonstrations of local adaptation, there are few studies identifying the agent or target of selection.

Given that organisms typically live in complex communities, interacting species, such as symbiotic microbes, may influence plant adaptation to abiotic stressors. My dissertation project explores how resource mutualists influence plant adaptation to soil moisture in the field. Using the model legume-rhizobia mutualism, my research aims to expand our understanding of the mechanisms contributing to local adaptation, how species interactions influence local adaptation, and the traits underlying adaptation.


Ecological and Evolutionary Effects of Herbicide on Plant-Microbe Interactions

Collaborators: Jennifer Lau (MSU) and Jay Lennon (Indiana University)

At soybean field.

In soybean field.

Exposure to novel environmental stressors, such as chemical pesticides, has been shown to reduce population growth rates of plants, animals, and microorganisms. However, these novel stressors could also alter the evolution of exposed populations if genotypes differ in their response to the stress. We are conducting combination of field, greenhouse and laboratory experiments to examine the ecological and evolutionary consequences of a novel environmental stress, herbicide application, on the soybean (Glycine max) and rhizobia (Bradyrhizobium japonicum) mutualism.



Quantifying Non-Additive Selection Caused by Indirect Ecological Effects

Collaborators: C.P. terHorst, , J.A. Lau, I.A. Cooper, K.R. Keller, R.J. LaRosa, A.M. Royer, E.H. Schultheis and J.K. Conner.

In natural communities, species interact with many other organisms. Although many studies have estimated selection gradients in pairwise species interactions, these estimates may not predict selection in response to multiple species interactions, if selection is non-additive. In collaboration with members of the Lau lab and Conner lab at KBS, we developed an experimental and statistical approach to quantify the relative strength of non-additive selection as a result of indirect ecological effects compared to the strength of pairwise selection. We concluded that non-additive selection mediated by indirect ecological interactions may be common in natural communities (terHorst et al. 2015).

A Novel Impact of a Novel Weapon

Collaborators: C Portales-Reyes, T. Van Doornik, and E. H. Schultheis

gm exp

Greenhouse experiment

Invasive species threaten native plant communities, reducing biodiversity and changing community composition. Garlic mustard, a notorious invasive plant species in North America, has been shown to outcompete native species indirectly through its use of novel allelochemicals that reduce the abundance of mycorrhizal fungi mutualists, upon which many native plant species rely. Here, we tested the effects of garlic mustard’s allelochemicals on rhizobia. We found that garlic mustard’s allelochemicals cause mutualism disruption by preventing the formation of nodules, thereby reducing plant growth (Portales et al. 2015).

Does Mutualism Influence Legume Responses to Nitrogen Enrichment?

Collaborators: E. Grman, R. E. Prunier, M. Hammond and J.A. Lau

jertNitrogen (N) enrichment, a widespread global environmental change, has dramatic effects on plant communities, causing some species (“winners”) to increase in relative abundance and others (“losers”) to decrease, usually driving a net loss in biodiversity. Legumes are commonly amongst the losers in high N environments, potentially because although their mutualism with N-fixing rhizobia provides a competitive advantage in low N environments, this interaction is accompanied by substantial costs in high N environments. However, legumes vary in response to N, and this variation provides an opportunity to quantitatively test whether variation in traits related to mutualisms, or variation in other plant traits, determine legume response to N enrichment. Using nitrogen enrichment experiment plant community data sets from eight Long Term Ecological Research (LTER) sites and manipulative greenhouse experiments, we found that traits both related and unrelated to mutualism with N-fixing rhizobia may explain variation in legume species responses to long-term fertilization.

Effects of insect herbivory and plant competition on an introduced thistle

Cirsium vulgare (bull thistle)

Cirsium vulgare (bull thistle)

(Advisor: Svata Louda)

In my Master thesis, I examined the factors limiting biological invasion of introduced species. The biotic resistance hypothesis posits that strong interactions with the native community can limit introduction, establishment, and invasive spread of introduced species. Using introduced Cirsium vulgare and its native congener, Cirsium altissimum as study system, I conducted a series of field experiments, manipulating both competition by neighboring plants and herbivory imposed by native insects. I found that competition and herbivory limit the performance of introduced more than that of native species, suggesting that interactions with native communities can constrain an incipient biological invasion. For more info, you can check out thisthis and this paper.

Influence of nutrient availability on the mechanisms of tolerance to herbivory 

(Collaborator: Hafiz Maherali, University of Guelph)

Avena barbata

Photo Credit: J. R. Manhart

Tolerance is the capacity of a plant to reduce the negative effects by herbivores through compensatory growth and reproduction. It is estimated by difference in reproductive performance between damaged and undamaged plants and can evolve by natural selection only if there is genetic variation for tolerance. Using Avena barbata (wild oat) as a study system, we tested whether a) the level of herbivory tolerance is influenced by nutrient availability and b) nutrient availability affects the expression of genetic variation for tolerance. We focused on two key mechanisms of tolerance: biomass regrowth and upregualtion of photosynthesis. We found no evidence for photosynthetic upregulation in defoliated compared to control plants in either nutrient treatment. However, tolerance was positively correlated with predefoliation photosynthetic efficiency at high nutrients. We conclude that constitutive photosynthetic efficiency may be a better predictor of tolerance than photosynthetic responses to herbivory in A. barbata. For more info, you can check out this paper.