Browsing by Subject "Dormancy"

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    The Effect of Various Stratification Lengths on Seed Sources of Ambrosia artemisiifolia Across Latitudes
    (2017-04) Kim, Joo Yoon; Moeller, David A; Gorton, Amanda J
    Seeds dormancy, a period of ceased physiological activity, is an adaptive trait promoting survival of seeds. Many plants exhibit different germination rates when seeds from various locations where seeds exposed to winter length and temperatures of their origins, are treated to equal amount of cold stratification length. This particular trait is expressed in common ragweed (Ambrosia artemisiifolia). Ragweed has high reproduction of dormant seeds that persist in the soil for many years while maintaining germination ability. Seeds are dependent on environmental conditions such as day length, temperature and humidity to break seed dormancy. That way, the dependence of seeds on environmental condition acts as a monitor system to determine the optimal germination timing and avoid improper environmental conditions. One of the most crucial environmental conditions for ragweed seeds is stratification or a period of cold temperatures, which is the first process that induces the dormancy and later promotes germination. Ragweed seeds collected from various locations corresponding to different latitudes may have different germination rates because of different temperatures and stratification from their own habitats. A study by Sorenson et al. (1990) indicated northern seeds of species western larch (Larix occidentalis Nutt.) have higher germination rates under longer stratification lengths. In the other hand, a study by Karlsson et al. (2007) indicated South African, where maintain high temperatures, seeds of species Papaver aculeatum have higher germination rates under warmer stratification. Accordingly, ragweed seeds from northern locations may require longer stratification and colder temperature to break dormancy because of its strong dormant. By contrast, seeds from southern locations may not require such long periods of stratification for germination because they lack extended winters. As difference in germination rates from different seed populations can be evident in response to various stratification lengths with fixed temperature, in this experiment I investigated the effect of different stratification lengths on germination rates of seeds from populations with different winter length.
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    Physiology and dormancy of the aquatic angiosperm potamogeton crispus L. turions
    (2013-12) Heuschele, Deborah "Jo""
    Vegetative buds (turions) are the major source of propagation for the aquatic invasive angiosperm, Potamogeton crispus L. (Potamogetonaceae). An understanding of the regulation of turion dormancy could lead to better methods of population control. The majority of Potamogeton crispus turions remain dormant over the summer and sprout in the autumn, while a small subset of turions remain dormant for an unspecified time. Hormonal control of dormancy in aquatic plant vegetative propagules is not well understood. For this study turions were divided into two different age groups, newly formed (current season) and older than one year (overwintered). The effect of varying light durations and temperatures on sprouting was monitored in these different groups. Non-structural carbohydrates, photosynthesis, and aerobic respiration were measured to determine metabolic activity. We also measured abscisic acid concentrations and sprouting levels in turions that were exposed to various hormones, temperatures, and light durations to elucidate hormonal control of dormancy. Current season turions were found to sprout mainly in response to day length and were metabolically active over a 6 week period. They are in a semi-dormant state and 60-70% will sprout in the autumn. The remaining current season turions presumably go into a state of deep dormancy and remain dormant over the winter. Turions that have overwintered are not photosynthetically active, have stable carbohydrate levels, and can remain dormant but viable for several years. Under laboratory conditions, they sprouted mainly in response to an increase in water temperature. These different age groups correspond to different turion physiological states and can explain sprouting variability recorded by other researchers. Current season turions produce and sprout in response to changes in ABA levels. A reduction of ABA in new turions is correlated with the breaking of dormancy. Overwintered turions do not sprout in response to ABA or GA changes. The results indicate two different pathways utilized by P. crispus turions to maintain and break dormancy.