The Effect of Various Stratification Lengths on Seed Sources of Ambrosia artemisiifolia Across Latitudes

Abstract

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.