Browsing by Author "Gorton, Amanda J"

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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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    An urban-rural spotlight: evolution at small spatial scales among urban and rural populations of common ragweed
    (2021-01-12) Kostanecki, Adam; Gorton, Amanda J; Moeller, David A; kosta025@umn.edu; Kostanecki, Adam; University of Minnesota Moeller Lab
    Urbanization produces similar environmental changes across cities relative to their neighboring rural environments. However, there may be high environmental heterogeneity across an urban-rural gradient. Previous research in Minneapolis, MN, USA, found mixed evidence that urban and rural plant populations of common ragweed have locally adapted, and that urban populations exhibit greater among-population divergence in ecologically-important traits. To investigate whether there are parallel patterns of urban-rural trait divergence across different urban areas, we examined trait variation across an urban-rural gradient in a second city, St. Louis, MO, USA. We used growth chamber and greenhouse common environments to investigate variation in six traits within and among 16 populations of common ragweed (eight from each urban and rural area). Urban and rural plants diverged significantly in three of five traits, with rural plants having lower percent germination, greater height and lower leaf dissection index. We also found greater variance in plant height among urban compared to rural populations, potentially driven by heterogeneity in human management practices on urban populations. Patterns of urban-rural trait divergence (e.g. in flowering time) differ substantially from those found previously in the reciprocal transplant experiment in Minneapolis, contradicting the hypothesis of parallel evolution across different metropolitan areas. The results of this study suggest that there is considerable population variation in ecologically-important traits, but that urban populations do not consistently differ from neighboring rural populations.