Mutualisms are ubiquitous in nature, yet these interactions often vary in strength and persistence over space and time. 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 using mycorrhizal associations, symbiotic interactions between plants and root-colonizing fungi.
An estimated 80% of plant species associate with mycorrhizae, providing their fungal partners with carbon in return for soil resources. Mycorrhizal associations are generally viewed as mutualisms; however, mycorrhizal effects often depend on the biotic and abiotic context. To better understand mechanisms underlying the strength and distribution of mutualisms I compared mycorrhizal associations in co-occurring alpine host species and along natural gradients in environmental conditions.
First, I examined the distribution of arbuscular mycorrhizae (AM) across the willow-meadow ecotone at treeline on Pennsylvania Mountain (Park County, CO, USA). Specifically, I compared AM colonization, richness, diversity, and composition in Taraxacum ceratophorum, T. officinale, Polemonium delicatum , and P. viscosum in open meadow and willow understory habitats. Results indicate that AM associations are more abundant and more species-rich in the open meadow, and that host species differ in their associations with AM fungi. These results highlight the context-dependent nature of mutualisms, and suggest 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 experiments indicate that alpine willows indirectly influence AM colonization through feedbacks with ectomycorrhizae (ECM) and leaf litter deposition. Greenhouse experiments further suggest that resource availability influences net mycorrhizal effects in Taraxacum hosts. Together these studies suggest that biotic and abiotic factors alter partner benefits, thereby generating variation in these mutualisms.
Finally, I evaluated implications of variation in mycorrhizal associations by examining the role of mycorrhizae in plant invasions, aboveground interaction webs, and the evolution of plant traits. Results from one study indicate that mycorrhizae influence the distribution and performance of T. officinale , an invasive species in North American alpine communities. In a second study, mycorrhizae influenced the behavior of floral visitors to P. viscosum and the potential for insect-mediated selection on floral traits. Both studies demonstrate the potential for mutualisms to impact the broader ecological community and evolutionary processes.
Overall, this research advances our understanding of mutualism, highlighting the inherent complexity of these interactions and their importance to ecological and evolutionary processes. Furthermore, comparisons between native and exotic congeners establish a model system for answering questions about the ecology and evolution of mycorrhizae. Finally, my research supports the prediction that mycorrhizal associations are important in alpine plant communities and suggests that factors disrupting these interactions may have significant consequences for alpine ecosystems.
|School:||University of Missouri - Columbia|
|School Location:||United States -- Missouri|
|Source:||DAI-B 73/03, Dissertation Abstracts International|
|Subjects:||Plant biology, Ecology|
|Keywords:||Alpine, Ecotone, Mutualism, Mycorrhizal associations, Plant-fungus interactions|
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