Silva, LucasDawson, Hilary Rose2025-02-242025-02-24https://hdl.handle.net/1794/30469Leaf traits represent the wide variety of leaf forms plants have evolved to maximize carbon gains over their lifetimes. Although extensive research supports the use of these physiological metrics, much variation in leaf traits remains unexplained. In this thesis, I address three influences on leaf trait variation: leaf ontogeny, environmental stress, and cross-kingdom interactions.In the first study, I use two evergreen dwarf shrubs as case studies to demonstrate that leaf traits vary depending on cohort (current year’s growth or previous year’s growth) in Vaccinium vitis-idaea and Empetrum nigrum. Despite this difference, researchers often do not specify which cohort they measured or differentiate between the cohorts. In the second study, I test how plant form and function hold in herbaceous prairie species under experimental drought conditions in a U.S. Pacific Northwest grassland. I found that plant form-function relationships were robust against drought, and leaf traits remained unchanged. In the third study, I used stable isotope tracers to determine if common mycorrhizal networks favor fungal resource acquisition at the expense of plant resource demands, or if they are passive channels through which plants regulate resource fluxes. I found that plant functional type and tissue stoichiometry were the most important predictors of interspecific resource transfer. This dissertation includes previously published and unpublished coauthored material.en-USAll Rights Reserved.Climate changeDroughtForm-function relationshipsLeaf ontogenyLeaf traitsMycorrhizal fungiElectronic Thesis or Dissertation