Friends in high places: ecology of mycorrhizal associations in alpine plant communities
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Mutualisms are ubiquitous in nature, yet these interactions often vary in strength and persistence. This variation raises the questions of what determines whether mutualisms persist or vanish, and how does variation in the strength of mutualisms affect populations, communities, and ecosystems. I addressed these questions by evaluating mycorrhizal associations, symbiotic interactions between plants and root-colonizing fungi, in co-occurring alpine plant species along an environmental gradient. First, I examined the distribution, diversity, and composition of mycorrhizal fungi across the willow-meadow ecotone at treeline on Pennsylvania Mountain (Park County, CO, USA). Results highlight the context-dependent nature of mutualisms and indicate that both biotic and abiotic factors determine the strength of these associations. Next, I identified environmental factors that contribute to variation in mycorrhizal associations across the willow-meadow ecotone. Field and greenhouse studies indicate that biotic and abiotic factors alter partner benefits, thereby generating variation in these mutualisms. Finally, I evaluated implications of variation in mycorrhizal associations for plant populations and communities. Results of two studies demonstrate the potential for mycorrhizae to impact plant invasions, aboveground interaction webs, and the evolution of plant traits. Overall, this research advances our understanding of mutualism, highlighting the inherent complexity of these interactions and their importance to ecological and evolutionary processes.