Graduate Thesis Or Dissertation

 

Impacts of dwarf mistletoe on the physiology of host Tsuga heterophylla trees as recorded in tree ring C and O stable isotopes Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/qb98mh80k

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  • Dwarf mistletoes, obligate, parasitic plants with diminutive aerial shoots, have long-term effects on host tree water relations, hydraulic architecture, and photosynthetic gas exchange and can eventually lead to tree death. To investigate the long-term impacts of dwarf mistletoe on gas exchange of host western hemlock trees, I compared growth, gas exchange, and tree-ring cellulose stable carbon and oxygen isotope ratios (δ¹³Ccₑcell and δ¹⁸Ocₑcell) of heavily infected and uninfected trees. Relative basal area growth declined more rapidly with increasing tree size in infected than uninfected trees. Both radial growth and δ¹³Ccₑcell was significantly lower in infected than uninfected trees when trees were heavily infected. The combination of radial growth and δ¹³Ccₑcell patterns described the intensification of dwarf mistletoe throughout tree crowns through time. δ¹³Ccₑcell and δ¹⁸Ocₑcell were significantly lower in infected trees than uninfected trees, an unexpected result given that stomatal conductance, relative humidity and other external variables expected to influence the δ¹⁸O values of leaf water were similar for infected and uninfected trees. Leaf mesophyll conductance (gm) and effective pathlength (L) were estimated to explain observed differences in δ¹⁸Ocₑcell between infected and uninfected trees. Infected trees had significantly lower gm and greater L than uninfected trees. These results point to the limitations of the dual isotope approach for identifying sources of variation in δ¹³Ccₑcell and indicate that changes in leaf internal properties such as L that affect δ¹⁸Ocₑcell must be considered. The significantly greater L and significantly lower gm in infected compared to uninfected trees suggest that dwarf mistletoe may influence leaf structural and anatomical characteristics that are related to L and gm.
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