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Sensitivity in growth responses of tree seedlings to variation in identity and abundance of ectomycorrhizal fungi Karst, Justine Delaney


Interdependent organisms such as trees and ectomycorrhizal fungi are described as coevolved. Partner species in coevolved interactions are expected to be sensitive to intraspecific variation of each partner due to the intimate and interdependent nature of their interactions. In this thesis, I considered specific aspects of variation in each of the ectomycorrhizal partners and how this variation influenced the other partner. In particular, I used experimental and meta-analytical approaches to evaluate (1) how colonization levels, regardless of ectomycorrhizal fungal taxon, correlated to host growth; (2) how ectomycorrhizal fungi differentially influenced growth of different genera of plant hosts, and (3) how variation in growth of a single host species was correlated to the composition of ectomycorrhizal fungal communities in various soil environments. Because controlling for and manipulating ectomycorrhizal fungi on host plants is integral to these questions, I also tested the efficacy of two methods to control colonization by ectomycorrhizal fungi on host plants and found that fungicides and mesh can be effective barriers to colonization. Results from the meta-analysis and experiments indicated that colonization levels did not consistently scale with host growth response, however, suggesting that colonization levels may not be an ecologically useful factor to gauge the growth responses of host plants to ectomycorrhizal fungi. In addition, there was little sensitivity in growth responses of host plants to variation in the identity of ectomycorrhizal fungi. Seedlings across multiple host genera increased in biomass and shoot height when inoculated with ectomycorrhizal fungi regardless of the identity of the fungal associate. When ectomycorrhizas were considered in a multi-specific context (i.e. one host species associated with a community of ectomycorrhizal fungi), variation in host shoot properties was not correlated with species composition of the community of ectomycorrhizal fungi on their roots but rather appeared to be coupled to edaphic conditions. These results indicate that the variation in ectomycorrhizal fungi perceived and selected for by the host plant may be of a discrete (presence/absence of ectomycorrhizal fungi) rather than continuous nature (variation in identity or abundance of ectomycorrhizal fungi).

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