Continental Diversity of Chenopodium album Seedling Recruitment

Chenopodium album seedling emergence studies were conducted at nine European and two North American locations comparing local populations with a common population from Denmark (DEN-COM). Mortality risk. Weedy plant life history conforms to the time of mortality risk from either the environment (e.g. frozen soil in the winter) or cropping systems practices (e.g. herbicide use). C. album life histories are constrained by the environmental and cropping system practices of a locality. It is hypothesized that C. album seedling recruitment timing and magnitude have adapted to these local conditions and are expressed in emergence behavior. Recruitment periodicity and quantity were found to be closely related to predictable cropping system disturbances, experimentally induced disturbances, and seasonally-available plant resources and conditions. Recruitment patterns were the consequence of seasonal limitations in the habitat (filter 1), predictable cropping system disturbances (filter 2) and experimentally induced disturbances to simulate early season tillage. As a consequence of these filters C. album seized locally available seedling emergence opportunity. Filter 1: Habitat. Limitations in the habitat (filter 1) are reflected in local C. album population recruitment season length: Julian weeks (JW) 2-37, duration 12-37 weeks. Generally, the duration of seedling recruitment (undisturbed, experimentally disturbed) of both populations (local; DEN-COM) increased with decreasing latitude, north-to-south. In general, compared to the local population, DEN-COM recruitment at locations north of Denmark was longer and south of Denmark was shorter, and ended sooner. The early season onset of recruitment was more consistent than that in the late season, which had smaller numbers and greater variability over longer times. Autumnal recruitment in the burial year (2005) occurred at a few locations. Filter 2: Cropping disturbance. Predictable, historical, seasonal times of local cropping system disturbances (CSD) provided the second filter of seedling recruitment opportunity. Generally, the CSD period increased with decreasing latitude, with some exceptions. The total duration of the CSD period was over twice as long in the south as that in the north. After layby there occurred a mid-season period of CSD inactivity at all locations, the post-layby (PL) period, when cropping activity ceases. This post-layby period was from JW 21-34, with durations of 2-13 weeks, depending on location. No CSD's occurred at any location during JW 26-29, excepting the UK Seedling emergence structure: time, number. Recruitment at each locality possessed seasonal structure (time, number) consisting of 2-4 discrete seasonal cohorts, a consequence of habitat and disturbance limitations. The spring cohort (JW 12-24) …