Pollen performance of Raphanus sativus (Brassicaceae) declines in response to elevated [CO(2)].

Although increases in atmospheric [CO(2)] are known to affect plant physiology, growth and reproduction, understanding of these effects is limited because most studies of reproductive consequences focus solely on female function. Therefore, we examined the effects of CO(2) enrichment on male function in the annual Raphanus sativus. Pollen donors grown under elevated [CO(2)] initially sired a higher proportion of seeds per fruit than ambient [CO(2)]-grown plants when each was tested against two different standard competitors; however, by the end of the 5-month experiment, these pollen donors sired fewer seeds than ambient [CO(2)]-grown plants and produced a lower proportion of viable pollen grains. The results of this experiment confirm that elevated [CO(2)] can alter reproductive success. Additionally, the change in response to elevated [CO(2)] over time varied among pollen donor families; thus, changes in [CO(2)] could act as a selective force on this species.

The impact of plant and flower age on mating patterns.

BACKGROUND: Over a season, plant condition, amount of ongoing reproduction and biotic and abiotic environmental factors vary. As flowers age, flower condition and amount of pollen donated and received also vary. These internal and external changes are significant for fitness if they result in changes in reproduction and mating. SCOPE: Literature from several fields was reviewed to provide a picture of the changes that occur in plants and flowers that can affect mating over a season. As flowers age, both the entire flower and individual floral whorls show changes in appearance and function. Over a season, changes in mating often appear as alteration in seed production vs. pollen donation. In several species, older, unpollinated flowers are more likely to self. If flowers are receiving pollen, staying open longer may increase the number of mates. In wild radish, for which there is considerable information on seed paternity, older flowers produce fewer seeds and appear to discriminate less among pollen donors. Pollen donor performance can also be linked to maternal plant age. Different pollinators and mates are available across the season. Also in wild radish, maternal plants appear to exert the most control over paternity when they are of intermediate age. CONCLUSIONS: Although much is known about the characters of plants and flowers that can change over a season, there is less information on the effects of age on mating. Several studies document changes in self-pollination over time, but very few, other than those on wild radish, consider more subtle aspects of differential success of pollen donors over time.

Do differences in plant and flower age change mating patterns and alter offspring fitness in Raphanus sativus (Brassicaceae)?

When more pollen is present on stigmas than needed to fertilize all ovules, selection among pollen grains may occur due to effects of both pollen donors and maternal plants. We asked whether increasing plant age and flower age, two changes in maternal condition, altered the pattern of seed paternity after mixed pollination. We also asked whether changes in seed paternity affected offspring success in an experimental garden. While flower age did not affect seed paternity, there was a dramatic shift in pollen donor performance as plants aged. These differences were seen in the offspring as well, where the offspring of one pollen donor, which sired more seeds on young plants, flowered earlier in the season, and the offspring of another pollen donor, which sired more seeds on old plants, flowered later in the season. Thus, change in maternal condition resulted in altered seed paternity, perhaps because the environment for pollen tube growth was different. The pattern of seed paternity and offspring performance suggests that pollen donors may show temporal specialization.

Differences in plastic responses to defoliation due to variation in the timing of treatments for two species of Sesbania (Fabaceae).

BACKGROUND AND AIMS: Plastic responses to stress in components of reproduction can have important effects on plant fitness and can vary both within and between species. Responses may also depend on when in the life cycle stress occurs. Here, it is predicted that the timing of initiation of a stress, defoliation, would affect the pattern of plastic responses. These differences should occur because some components of reproduction, such as flower number, are determined earlier in a plant's life than others, such as individual seed mass. METHODS: To test this prediction, 50 % artificial defoliation treatments were initiated at four different times for Sesbania macrocarpa and S. vesicaria. Responses were measured in plant size, number of flowers, number of flowers/plant size, fruit set, number of seeds per fruit, individual seed mass and total seed mass per plant. KEY RESULTS: For S. vesicaria, changes in the timing of stress changed the severity, but not the pattern of response. For S. macrocarpa, plastic responses to defoliation varied strikingly between early and late treatments. Late treatments resulted in over-compensation in this species. Sesbania macrocarpa was generally more plastic than S. vesicaria and the species showed opposite responses for most components of reproduction. CONCLUSIONS: While there were effects of timing of defoliation and differences between species, the nature of these effects did not precisely fit our predictions. Our results suggest that differences in the length and flexibility of the life cycles of the two species allowed for unexpected variation in responses. For example, because flower production continued after the last treatment in S. vesicaria, responses were not constrained to reductions in individual seed mass.