Semester

Summer

Date of Graduation

2012

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Jonathan Cumming.

Abstract

Poplar species and hybrids are intensively cultivated as renewable sources of biomass because of their rapid growth, extensive genetic variation and ease of propagation. However, the physiological mechanisms underlying soil stress resistance within these poplar species and hybrids are not yet understood. With the recent sequencing of the poplar genome, the use of this species in physiological stress resistance studies may help elucidate the underlying basis of stress resistance in a woody species. Further, although symbiotic mycorrhizal associations have farreaching ecological significance in forest ecosystems, our understanding of the influences of the association on the genetic basis of environmental stress resistance of trees, including poplar, is limited.;In this dissertation research, physiological, ecophysiological, proteomic and plant biochemistry approaches were used to understand the role of the plant-mycorrhizal symbiotic association under P limitation. By using advanced technology, such as proteomics including two-dimensional gel electrophoresis, in association with physiological measures, my research has aimed to understand the role of the mycorrhizal association in tree stress physiology, which has global implications..;My objective for the first chapter was to test if the association of the ectomycorrhizal fungus Laccaria bicolor (Marie) with aspen (Populus tremuloides Michx.) would alter the plant response to environmental phosphate (Pi) limitation. To test this, we studied different stress related oxidative enzymes, such as catalase and superoxide dismutase, carbon allocation of above and below ground biomass, tissue P accumulation, and root exudation of organic acids. The symbiotic association improved P acquisition in aspen and reduced the oxidative stress responses as well as the exudation responses generated by P limitation. The results confirmed that the acclimation responses of aspen in association with Laccaria bicolor under Pi limitation were mediated through enhanced Pi uptake resulting from the symbiotic association.;In the second chapter, I assessed a broader set of physiological changes in aspen under P limitation due to the different ectomycorrhizal species, Laccaria bicolor and Paxillus involutus. I hypothesized that aspen would have more carbon demand belowground due to mycorrhizal colonization and, to meet this demand, carbon assimilation would increase. Secondary metabolites are also indicators of stress and glycosides in aspen are well defined (Chen et al. 2009). Hence I assayed the secondary metabolites in different plant tissues. As the two fungal species differ in their occurrence, we expected their behavior to differ for the ecophysiological and secondary metabolite parameters. In this study, I found that P limitation significantly limits photosynthetic gas exchange as well as the biochemistry of photosynthesis, but primarily in nonmycorrhizal aspen. These changes were correlated with reductions in tissue P levels that were pronounced in nonmycorrhizal plants.;Finally, to gain a better understanding of the molecular mechanisms of the mycorrhizal symbiotic association, I used proteomic approaches to evaluate the proteins involved in this interaction. The analysis of the proteins that were differentially displayed during ectomycorrhizal and arbuscular mycorrhizal association visualized by two-dimensional electrophoresis (2-DE) of the total protein obtained from poplar roots non-inoculated and associated with two ectomyccorhizal fungi L. bicolor and P. involutus and one arbuscular myccorhizal fungus Glomus intrradices , were analyzed. I found significant changes in protein abundances in many metabolic pathways, including those associated with energy, general metabolism, and stress response induced by the arbuscular and ectomycorrhizal association. Similarities and differences between the two groups of fungi suggest that there may be both conserved and unique plant responses to mycorrhizal colonization.;By using the different tools of physiology, ecophysiology, plant biochemistry and proteomics, I attempted to build a broad understanding about the symbiotic association. This research will help to accelerate our understanding of the plant-soil interface and tree stress physiology, which in turn can aid in our understanding of forest ecosystem productivity and response to future changes in the environment. (Abstract shortened by UMI.).

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