Semester of Graduation
Summer 2025
Degree Type
Dissertation/Thesis
Degree Name
Master of Science in Integrative Biology
Department
Ecology, Evolution, and Organismal Biology
Committee Chair/First Advisor
Mario Bretfeld
Second Advisor
Nicholas Green
Third Advisor
Thomas McElroy, Matthew Weand
Abstract
The American chestnut, Castanea dentata, was once a dominant tree species in the forests of eastern North America until it was deemed functionally extinct due to the fungus, Cryphonectria parasitica, that caused the chestnut blight. Restoration efforts have been underway to restore the tree to its native range using backcross breeding with the Chinese chestnut, Castanea mollissima. Hybridized species are bred to retain morphological characteristics of the American chestnut but include blight resistance of the Chinese genotype. Although a few studies have examined leaf characteristics such as stomatal density and leaf mass per area (LMA) in wild-type and hybrid trees, no known studies have characterized their phyllosphere communities, and only a limited number have investigated leaf decomposition and heterotrophic respiration of senesced leaves. With the potential for hybrid reintroduction, it is important to understand how hybrid leaf characteristics, microbiomes, and decomposition compares to those of the wild-type American counterpart, and whether hybrids could occupy the same ecological niche. A three-part study was conducted to examine leaf characteristics, bacterial and fungal microbial communities, and heterotrophic respiration of the leaves from American, Chinese, and two hybrid genotypes of chestnuts. It was hypothesized that phyllosphere communities and heterotrophic respiration rates would differ between American, Chinese, and hybrid genotypes. It was also hypothesized that leaf morphology and genetic makeup of American chestnut trees are better predictors of phyllosphere microbial species diversity and community composition than location. To test these predictions, leaves from American, Chinese, and hybrid (B3 and B3F3) trees were collected from two orchard locations. Leaf Mass Area and stomatal densities were measured, DNA extractions were performed, and a heterotrophic respiration study was conducted. Results showed that microbiome communities did differ among genotypes. Leaf characteristics were not indicative of phyllosphere differences, but genotype, and to a lesser extent, location, were. Heterotrophic respiration differed in one hybrid species (B3F3). Overall, results suggest that hybrid chestnut leaf morphology and microbiomes more closely resemble American genotypes than Chinese genotypes. These findings are promising for reintroduction efforts, but additional research is needed.
Comments
Thank you to the Department of Ecology, Evolution, and Organismal Biology (EEOB) at Kennesaw State University for providing funding to support my project.