  Chenopodium album seedling emergence studies were conducted at nine European
and two North American locations comparing local populations with a common
population from Denmark. It is hypothesized that C. album seedling recruitment
timing and magnitude have adapted to environmental and cropping system
practices of a locality. Limitations in the habitat (filter 1) were reflected
in local C. album population recruitment season length. Generally, the duration
of seedling recruitment 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. Generally, the local cropping
system disturbances (CSD) period increased with decreasing latitude. The total
duration of the CSD period was over twice as long in the south as that in the
north. Recruitment at each locality possessed seasonal structure (time, number)
consisting of 2-4 discrete seasonal cohorts. This may be an adaptive means by
which C. album searches for, and exploits, recruitment opportunity just prior
to, and after, predictable disturbances. The control of C. album seedling
emergence is contained in the heteroblastic traits of its locally adapted
seeds, and is stimulated by a complex interaction of light, heat, water,
nitrate and oxygen signals inherent in the local environment. Our observations
of complex recruitment patterns occurring at critical cropping times is strong
evidence that C. album possesses a flexible and sensitive germination
regulation system adaptable to opportunity in many different Eurasian and North
American agricultural habitats.
