Electronic Theses and Dissertations for Graduate School
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Root phenology in a changing world
Restricted (Penn State Only)
Doctor of Philosophy
Date of Defense:
November 16, 2016
David Eissenstat, Dissertation Advisor
David Eissenstat, Committee Chair
Eric Post, Committee Member
Margot Kaye, Committee Member
Kathleen Brown, Outside Member
Shifts in plant phenology have been widely reported in response to global warming, and they can have strong effects on ecosystem processes and greenhouse gas emissions. Temperature is widely cited as the most important factor controlling the timing of aboveground growth, but the effects of warming on belowground phenology are poorly understood. Because root and shoot phenology may not be synchronous and may not be influenced by warming in the same way, root phenology research is critical to understanding shifts in whole-plant growth with climate change. In order to more fully understand the drivers of root phenology, in Chapter 1 we conducted a literature review of root phenology studies and determined that only 29% of these studies examined phenology in a highly quantitative way. We propose that if future studies quantitatively examine different phases of annual root phenology separately, specifically root initiation, peak, and cessation, we may be able to better understand the drivers of root phenology. In Chapter 2, we carried out this idea by quantitatively examining root initiation, peak, and cessation in a long-term dataset of grape root phenology. We determined that drivers of phenology above- and belowground are not likely to be the same, and drivers may change throughout the year. In Chapter 3 we examined the influence of experimental warming and herbivore exclusion on phenology in the Arctic. In this study, we found that warming did not affect roots in the same way as leaves, because warming advanced leaf phenology but not root phenology. We conducted a similar experimental warming study in Chapters 4-5, in which we compared the influence of warming on two vegetation types. Warming had minimal impacts on phenology above- and belowground at this site. Additionally, in contrast to expectations, root growth was not a primary driver of carbon exchange despite high root:shoot ratios at this site. Because direct drivers of root phenology are still unclear, future efforts should continue this line of research and use manipulative, controlled studies.
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