Title: Understanding Whole-Plant Nonstructural Carbohydrate Storage in a Changing World
Abstract: Nonstructural carbohydrates (NSCs) play a critical role in plant physiology and metabolism. They serve as building blocks for growth, fuel for respiration, and solutes for cellular regulation, but they can also be stored in the form of sugars and starch, with allocation timescales spanning minutes to decades. When stored, this reserve acts as a “food pantry” that enables sessile, long-lived plants to survive during unfavorable environmental conditions when their ability to make new NSCs is impaired. While there is growing evidence linking NSCs with stress tolerance and survival, critical questions about the size of the carbohydrate “food pantry” and how quickly it is used up and replenished remain unresolved. This knowledge gap hinders our ability to predict plant resilience to biotic and abiotic stress in a changing world, which has broader implications for understanding both short-term and long-term C storage and cycling at the whole-plant and ecosystem levels. In Chapter 1, I compared carbohydrate storage in temperate species at Harvard Forest (Petersham, MA) to determine the size and seasonal dynamics of whole-tree NSC reserves over the course of a year. These field-based NSC data were then scaled up to the forest ecosystem level and compared to estimates from commonly used ecosystem and land surface models. In Chapter 2, I built upon this work by characterizing the radial patterns in the concentration and age of NSCs within organs to gain insight into the availability of NSC reserves. In Chapter 3, I combined a long-term warming experiment with 13C-CO2 pulse labeling and compound-specific isotope analysis to trace sugars throughout whole-trees in the field (Richmond, NSW). This allowed for the assessment of carbon dynamics in response to warming representative of future temperature predictions for Australia. In Chapter 4, I quantified the seasonal dynamics of NSCs in boreal species at SPRUCE (Bovey, MN), a large-scale global change experiment using open-top chambers. This initial work explored shrubs and trees outside of the chambers and will inform long-term plant responses to elevated CO2 and temperature within the chambers. Overall, this dissertation provides insight into whole-plant carbon storage and allocation under current and future climatic conditions.
Committee: N. Michele Holbrook (Advisor), Charles Davis, Elena Kramer