title: Growth schedule of Xanthium canadense: Does it optimize the timing of reproduction?
abstract: The effects of nutrition on the timing of reproductive initiation of a short-day annual plant Xanthium canadense (cocklebur) were examined with the following hypotheses in mind: If the plant always follows an optimal growth schedule, low-nutrient plants will initiate reproductive growth earlier than high-nutrient plants. On the other hand, if the plant flowers in response to photoperiodic stimuli, both plants will initiate reproductive growth on the same day. The sand-culture experiment showed that high-nutrient plants flowered earlier than the low-nutrient plants, leading to rejection of the first hypothesis. The predicted optimal flowering time is 2 days later than the actual flowering time in high-nutrient plants and 10 days earlier in low-nutrient plants. These deviations from the optimal times reduced the reproductive yield by 0.1% and 2.3%, respectively. The ratio of the final reproductive yield to the vegetative mass at flower initiation was 1.10 in high-nutrient plants and 0.63 in low-nutrient plants. Since the expected ratio for the optimal growth schedule is 1.0, high-nutrient plants followed the opitmal growth schedule more closely than the low-nutrient plants. Cocklebur is a fast-growing annual which is common in relatively nutrient-rich environments. This study suggests that cocklebur adapts itself to such environments through its photoperiodic response.
authors.affiliation: Biological Institute, Faculty of Science, Tohoku University, Aoba, 980, Sendai, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Sugiyama
authors.affiliation: Biological Institute, Faculty of Science, Tohoku University, Aoba, 980, Sendai, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Hirose
keywords: Annual plant; Nutrition; Optimization; Reproductive allocation; Xanthium canadense