Graduate Thesis Or Dissertation
 

Chlorophyll fluorescence as a measure of cold hardiness and freezing stress in 1 + 1 Douglas-fir seedlings : response to seasonal changes in the nursery

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  • Two-year old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings from two seed lots of different predicted hardiness levels were grown in two separate nurseries. Seedlings were lifted every four weeks from early October 1991 through March 1992 and exposed to controlled freezing temperatures. Fluorescence emissions of the seedlings were measured prior to freezing tests. After freezing, seedlings were measured one and three days following each freezing event and destructive morphological assessments were made seven days after the freezing events. Unstressed seedlings were measured six additional test periods from May through September 1992. The relationship between variable chlorophyll fluorescence (Fv) and stage of development and the effects of freezing injury on Fv were determined in Douglas-fir seedlings. Ten seedlings from each of the test temperatures were measured for F0 (ground fluorescence), F, and Fm (maximum fluorescence) emissions after being subjected to freezing events. There was no significant linear relationship between the control Fv/Fm ratio and the hardening development of the seedlings. The LT50 (lethal temperature to 50% of the seedlings) fluorescence measurements, however, appeared to be lower when the seedlings were not hardened off and higher once the seedlings were hardened off. Fv/Fm had a significant linear relationship to needle damage and survival.
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