Comparing early seedling growth of Centaurea stoebe from European (native), western North American and eastern North American seed sources

Background/Question/Methods

The invasion of western North America by a number of Centaurea species has had enormous ecological and economic impacts there. Surprisingly, though it is found in 47 of the 50 states many aspects of the life histories of these species are not as well known as they should be. Comparative studies and experiments in controlled environments are effective methods for understanding life history traits that we feel are underutilized. We present the results of a comparative greenhouse study on early seedling growth characteristics of Centaurea stoebe, which are important during establishment. We grew plants from seed collected from 3 regions: central Europe (native range), western North American (invasive range), and NY State, where it may be in a lag phase as an invader. Seeds were collected from Europe (Kyiv, Ukraine), two sites in eastern North America (Adirondack State Park and Long Island) and three sites in western North America (Idaho and California) were germinated and seedlings were grown in a greenhouse and harvested at 6 weeks (before the onset of flowering) to compare early seedling  characteristics. Total dry mass, shoot/root ratios and the timing of leaf rosette development were measured.

Results/Conclusions

Total biomass (shoots plus roots) was highest in plants originating from Europe, intermediate in New York and lowest in plants from western North America. Root growth was more extensive in the European natives and similar between plants with seed origins in the western U.S. and in New York State. Shoot to root ratio was highest in populations originating from the two New York regions, lowest in the native European region and intermediate in plants from western North America. Differences may be attributable to mechanisms such as the founder effect or in situ rapid evolution in the invaded habitat, or to maternal effects. Our results on rates of early growth contrast with predictions and some previous findings of larger plant size in the invaded relative to native habitats. We argue that much more information is needed from greenhouse, garden and field studies to better understand the early establishment characteristics and life histories of this important invasive species. Such information can address the different rates of invasion or the lack of harmful invasion in different areas of the introduced range.