Year of Award


Document Type


Degree Type

Doctor of Philosophy (PhD)

Degree Name

Organismal Biology and Ecology

Department or School/College

Division of Biological Sciences

Committee Chair

John Maron

Commitee Members

Ragan Callaway, John Klironomos, Ylva Lekberg, Anna Sala


University of Montana


Arbuscular mycorrhizal (AM) fungi are ancient mutualists that associate with the majority of plants. However, the factors that influence how much a plant benefits from AM fungi, or the factors that influence other root-associated fungi are unclear. I examined how plant traits related to nutrient availability can explain variation in AMresponsiveness and whether native species differ from exotics in these relationships. Leaf mass per unit of area (LMA) correlated positively with mycorrhizal growth responsiveness (MGR) and root colonization (RC) among native species. This indicates that native species with more conservative traits more strongly benefit, and benefit from, AM fungi. Furthermore, exotic species did not share this relationship, suggesting that ecological filtering can influence associations between plants and MGR.

I also investigated whether populations of the exotic plant, Centaurea solstitialis, collected from native versus non-native ranges, differed in AM-responsiveness. Grown alone, C. solstitialis from both ranges considered together derived a weak benefit from AM fungi, but in competition with the North American native S. pulchra, AM fungi ii i suppressed the biomass of C. solstitialis. The magnitude of this suppressive effect was greater on native versus non-native populations, suggesting that rapid evolutionary changes in how exotic plants respond to interacting AM fungal partners can affect their competitive tolerance in recipient communities.

Additions of N and of N and P can have strong effects on soil fungal community composition. However, it is unclear how individual guilds of fungi change along these gradients. I performed high-throughput sequencing on soils from the rhizosphere of Andropogon gerardii, the dominant C4 grass in the Konza Tallgrass Prairie Reserve, to investigate how long-term fertilization with N and N and P affect soil fungi. Fertilization increased pathogen abundance and diversity, but AM fungal abundance and diversity was only decreased when high amounts of P were added. Further, although most AM fungal species decreased along the fertility gradient, the dominant AM fungal species increased, suggesting potential shifts in the functional attributes of those communities. These results suggest that additions of N and P can increase rhizosphere pathogen loads and increases in P can shift the composition and abundance of AM fungi.



© Copyright 2015 Lauren Priestman Waller