Effects of apical damage on plant growth and male and female reproductive investments in Ambrosia artemisiifolia, a wind-pollinated plant

In wind-pollinated plants, apical damage may decrease male fitness by reducing height-dependent pollen dispersal distance, but may not affect female fitness because plant height is not always correlated with female fitness. We hypothesized that Ambrosia artemisiifolia responds to apical damage by (1) restoring plant height through compensatory growth from lateral buds, and/or (2) increasing the sex allocation to female function to compensate for the loss of male fitness. We tested these hypotheses by comparing a group of experimental removal of the apical meristem with three control groups and by field surveys on apically damaged plants. Experimental apical damage suppressed main stem growth, but promoted vertical secondary growth from lateral buds. These responses resulted in compensation of stem height in the apically damaged plants to the same height as one of three control groups. The numbers of male and female flowers and male racemes did not differ between damaged and undamaged plants, indicating that apically damaged plants did not change their sex allocation. Therefore, our results support our first hypothesis. The results of a field survey of naturalized populations also supported the first hypothesis in that plant height and the number of male racemes did not change in plants with apical damage. Consequently, our results suggest that A. artemisiifolia has a high ability of fitness compensation after apical damage by restoring height and male function. This ability may contribute to its invasiveness in disturbed habitats.