Date of Award:
Doctor of Philosophy (PhD)
Department name when degree awarded
Phenological studies of coneflower on aspen range in Northern Utah showed that resumption of growth of mature plants begins at the time of snow melt and the initial or rosette stage is completed between mid-May and mid- June. The rate of growth in this stage is controlled by temperature, being greater at higher mean temperatures. The bolting stage is completed about 1 week after the initiation of stem elongation and the process of capitulum development is begun. Flowering is initiated between late July and mid- August. Cross-pollination is necessary for seed set which is completed by the end of August. Seed dissemination is begun at that time and is completed by the middle of September. Altitude appeared to have an effect on the extent of seed filling, since collections from higher altitudes had lower percentages of filled seeds.
Seedling mortality increases as the season advances and reaches a maximum at the end of June when the associated species begin rapid growth. During the first season seedling growth is restricted to one unelongated stem and three leaves. Shoot/root ratios indicated that the main development during this season is in the roots.
Optimum controlled conditions for seed germination are alternating temperatures of 25 C-15C with 8 hour photoperiods coinciding with the periods of higher temperature. A constant temperature of 25 C or alternating temperatures of 15 C-5C or constant darkness under any of the temperature regimes give lower germination percentages.
Growth chamber studies demonstrated that coneflower is a long day plant since normal development to the seed setting stage is obtained under 18 hour photoperiods but not under 12 hour photoperiods when temperature alternations of 25 C-15 C are used. Low temperature stratification of the crown buds is not required for normal development.
A series of field experiments showed that coneflower does not inhibit the growth of an important associated grass species--mountain brome. Laboratory experiments with foliage leachate gave no evidence of inhibitory effects on the germination or growth of other species. Force-feeding of sheep with whole dried plants collected at the seed set stage showed no toxicity for these animals.
Total non-structural carbohydrates increase in the aerial parts of the plant as the growing season progressed up to the seed set stage and decreases thereafter until death of the aerial parts. Carbohydrates in the roots show a reverse trend.
Two or three clippings applied to the rosette stage resulted in death of the plants. Failure of regrowth after these clippings was probably due to exhaustion of the supply of mature buds on the crown rather than being due to exhaustion of food reserves since significant concentrations of nonstructural carbohydrates were still present in the roots of these dead plants.
Florez, Juan Arturo, "Ecological Life History of Rudbeckia occidentalis Nutt" (1971). All Graduate Theses and Dissertations. 6421.
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