The Recruitment Biology and Facultative Recruitment Nature of Conyza canadensis.
Conyza canadensis (Conyza canadensis (L.) Cronq. var. canadensis) is a surface-germinating ruderal facultative winter annual. The ruderal nature is a key adaptive characteristic that implicates emergence timing as an important recruitment factor. Experiments were established at three sites in southern Ontario, Canada from 2009 to 2012 and at the Thermogradient Plate at the University of Saskatchewan in 2011. Experiments in Ontario aimed to determine the possible effect of emergence timing of Conyza canadensis on survival, fecundity, and flowering timing in populations emerged seed sourced from Spain, United Kingdom, Ontario, and Iran as well as determine the effects of warming spell timing on survival, fecundity, aboveground biomass, and flowering timing for a population sourced from Ontario. Experiments at the Thermogradient Plate at the University of Saskatchewan aimed to determine a base germination temperature range and the amount of GGDs to 50% germination in seed sourced from populations in Spain, United Kingdom, Ontario, and Iran. Results indicated that seed shed timing parsed out into early/late spring or early/late fall helped observe differences between experimental factors. Overall, early fall and early spring emerging plants had significantly greater survival and fecundity, as well as shorter times to flowering when compared to late fall and late spring emerging cohorts in all populations. Results also indicated that warming spells closer to the spring season had a significantly larger negative impact on survival, fecundity, aboveground biomass, and flowering timing compared to warming spells occurring earlier in the winter season. Results conducted on the thermogradient plate indicated significant differences in base germination temperature range and the amount of GGDs to 50% germination in seed sourced from populations in Spain, United Kingdom, Ontario, and Iran, suggesting a genetic and therefore evolutionary difference between the international populations. Overall the findings emerging from this research suggest emergence timing plays a critical role in the population dynamics of Conyza canadensis and that this species has the potential to rapidly adapt to new climatic areas. These findings are especially important in a changing climate and may be exploited for better management approaches as herbicide resistant populations increase in frequency.