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The Ecological Drivers and Consequences of Grass Silicon Accumulation

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title
The Ecological Drivers and Consequences of Grass Silicon Accumulation
author
Quigley, Kathleen Quigley
abstract
Silicon (Si) comprises more than a quarter of earth’s crust by weight, and is an element accumulated in the leaf tissue of many early-diverging land plants, but relatively few angiosperms accumulate silicon. Grasses (Poaceae) are the only angiosperm family that incorporates vast (often > 5% of plant dry weight) amounts of silicon into their leaves as SiO2 bodies called phytoliths, and this biomineralization affords grasses numerous benefits. Researchers have long presumed that phytolith accumulation evolved to deter herbivory, as modern studies show that phytoliths abrade grazer mouthparts and interfere with digestion. However, recent phylogenetic analysis and consideration of the fossil record has shed some doubt on the hypothesis that Si accumulation evolved in order to reduce herbivory. In my dissertation research, I sought to identify the primary drivers of variation in plant silicification, focusing specifically on variation in grassland ecosystems. I developed novel methods to quantify plant silicon (Appendix F), which I then applied to studies at the individual, landscape, and global scale. At the individual plant scale, I found that soil silicon supply positively influences a broad range of plant morphological and physiological traits which emphasizes an important role of silicon in plant fitness (Chapter 1). In a common garden study of Serengeti grass species, I found that water supply, but not defoliation, resulted in induced silicon uptake (Chapter 2). In Serengeti’s highly heterogeneous soil landscape, I incorporated abiotic variation into a structural equation model, highlighting the importance of soil texture and plant-water relations in determining variation in grass leaf silicon (Chapter 3). Next, I highlighted the role of soil nutrients in driving leaf Si at grassland plots around the globe; importantly, I found no evidence of grazing-induced silicification at the global scale (Chapter 4). Finally, I performed a meta-analysis of previous plant Si studies, and I found that soil silicon supply and nitrogen availability were the only two stresses which consistently elicited a signal in grass Si concentration (Chapter 5). These findings are important because they challenge the existing paradigm in plant silicon research: that grazing is the primary adaptive force behind grass Si accumulation. Instead, my research emphasizes a clear role of soil nutrients and plant water relations in driving silicon uptake, a pattern which emerged across multiple spatial scales from the individual plant to the global scale.
subject
abiotic stress
grass
grazer
phytolith
plant defense
silica
contributor
Anderson, T. Michael (committee chair)
Madritch, Michael (committee member)
Anderson, David J (committee member)
Silman, Miles (committee member)
Kron, Kathleen (committee member)
Smith, William K (committee member)
date
2017-01-14T09:35:18Z (accessioned)
2018-01-13T09:30:10Z (available)
2016 (issued)
degree
Biology (discipline)
embargo
2018-01-13 (terms)
identifier
http://hdl.handle.net/10339/64172 (uri)
language
en (iso)
publisher
Wake Forest University
type
Dissertation

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