The evolutionary ecology of plant-fungal interactions

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The interaction between plants and fungi is one of the most ancient symbioses in nature, evolving more than 400 million years ago. Nearly all plants are colonized by soil fungi, and the symbiosis between plants and arbuscular mycorrhizal (AM) fungi is particularly common, influencing how nearly all plant lineages, including a majority of crop species, perceive and respond to their environment. Historically, this symbiosis was considered to be a mutualism because each partner can benefit from the interaction. AM fungi provide plants with nutrients from soil and plants provide AM fungi with sugars from photosynthesis. However, comparative surveys indicate that the magnitude of the benefit is variable and the growth of many plant species is suppressed in the presence of the symbiont. The proposed research will experimentally test why the symbiosis between plants and AM fungi varies in nature, and how it can impact the assembly of plant communities. First, we will determine whether the symbiosis can evolve in natural populations and experimentally identify the ecological causes of natural selection that favour greater growth benefits to plants. Second, we will test how root function influences the degree of benefit plants gain from the fungal partnership. Third, we will determine whether evolutionary change in the growth response of plants to AM fungi influences their ability to compete with other plants for limited resources. This knowledge will have three primary impacts. First, it can explain how variability in the symbiosis evolved and predict its evolution in response to future environmental changes. Second, knowledge of how root absorption of nutrients influences the symbiosis can inform crop breeding efforts designed to maximize plant benefits from the symbiosis. Third, knowledge of how the symbiosis influences plant competitive ability can improve understanding of the mechanisms of plant community assembly and thus contribute to management practices aimed at ecological restoration.