Semester

Summer

Date of Graduation

2006

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Jonathan R. Cumming.

Abstract

Aluminum (Al) in acidic soils is toxic to plants, affecting growth, water uptake, and nutrient assimilation. Aluminum resistance of plants has been ascribed to organic acid exudation from roots and changes in plant physiology resulting from the arbuscular mycorrhizal (AM) fungal symbiosis. This dissertation describes four studies that address questions regarding Al resistance of mycorrhizal plants.;In chapter 2, Liriodendron tulipifera, a common tree species in northeastern U.S. forests, was inoculated with several species of AM fungi and exposed to Al. Biomass and plant nutritional data showed that the AM species Glomus clarum conferred the most benefit to plant hosts. Organic acids exuded from roots, which can chelate and detoxify Al in root zones, appeared to be related the observed benefit of plants colonized by this species. In chapters 3 and 5, when Andropogon virginicus, an early successional species that colonizes disturbed soils, was inoculated with several AM species and isolates, plants colonized by G. clarum were larger than plants colonized by other species. However, organic acid exudation was not clearly associated with the growth benefits observed in plants in these experiments. In chapter 5, trends in the data showed that, under Al exposure, plants were larger when colonized by AM inoculum cultivated under prior Al exposure. The combined results of these studies illustrate functional variation among AM fungi and the importance of AM diversity in ecosystems. Additionally, cultivation of AM fungi under stressful conditions could enhance the stress resistance of AM fungi through the selection of stress resistance genotypes.;A field study, described in chapter 4, explored the relationship between plant succession and Al availability on the extreme soils of an abandoned coal mine. Concentrations of phytotoxic Al were low in vegetated areas compared to non-vegetated ones. Soil solution pH and organic acid concentrations were higher in vegetated locations at the end of the growing season and may be related to increased exudation as plants reached maturity or increases in decomposing leaf litter from senescing plants. Initial colonization of extreme sites by A. virginicus may ameliorate the low pH and Al conditions, facilitating ecological succession with other plant species.

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