The plastic and adaptive potential of sugar storage in temperate trees under climate change
Committee: Noel Michele Holbrook (Advisor), Robin Hopkins, Elena Kramer, Jonathan Thompson
Abstract: The ability to undergo plastic and evolutionary change in adaptive traits is key for plant survival under future climate change. Both processes require genetic variation in adaptive traits within populations. Thus, for my dissertation I measured genetic variation in nonstructural carbohydrates (NSC) storage concentrations, a critical trait that provides resilience to tree species during times of stress, within two common gardens. Both gardens had the same 1,100 genotypes, sourced from 19 different populations, and clonally replicated 3x at each site, as well as full genomic sequences for all genotypes. Common gardens are ideal as they control for differences in environment, allowing researchers to parse phenotypic differences due to genetics (ie. genetic variation). I sampled the branches, stems, and roots of black cottonwood (Populus trichocarpa) trees in two different Department of Energy (DOE) common gardens in January 2017.
In Chapter 1, I demonstrate the presence of locally adapted, genetic variation in NSC storage in the stems and roots of black cottonwood trees, indicating the potential for range-wide adaptive evolution. However, using a model of allele frequency distribution and climate, I predict that northern populations will be limited in their ability to adapt to future climates by a lack of genetic variation, while southern populations have high genetic diversity, but are at risk of local extinction due to more intense selective pressures.
In Chapter 2, I compare this genetic variation in NSC stores to genetic variation in other traits to look for locally adapted tradeoffs. I discover a tradeoff between NSC storage and diameter growth/fungal pathogen resistance when traits are relativized for differences in carbon supply. This tradeoff is not current locally adapted, but populations exhibit high variation in the degree to which plants store vs. grow/defend, indicating a strong evolutionary potential.
Finally, in Chapter 3, I explore genetic and plastic variation in branch total NSC concentrations and the proportion of NSC that resides in soluble sugars (ie. affect cell osmotic balance) and insoluble starch. I found genetic and plastic variation in both traits. Moving from the coastal (Clatskanie) to continental (Corvallis) garden, there was a 50% decrease in the average amount NSC stored as starch. While, there was no difference in the total amount of NSC concentrations between the two gardens, trees in Clatskanie grew much faster and were larger than trees in Corvallis, indicating that a NSC storage – growth tradeoff may be plastic.