Testing for cost of apical dominance in vegetation: a field study of three species

Damage to the shoot apex commonly causes release of lateral meristems from apical dominance in plants. This has been shown in some species to promote increased seed and/or biomass production (i.e. overcompensation) by stimulating lateral branching, primarily in plants growing free from competition for light. This may represent a potential fitness cost when apical dominance is left intact in non-competing plants. In this study, shoot apices of three herbaceous species, Hypericum perforatum L. (Hypericaceae), Melilotus alba Medicus (Fabaceae) and Ambrosia artemisiifolia L. (Asteraceae) growing in open habitats were removed in order to determine if a potential fitness cost of apical dominance was evident. We predicted that in such open habitats, where competition for light is relatively weak, there should be relatively little evidence for a potential cost of apical dominance; since there should be relatively little benefit in having apical dominance here, selection should minimize any potential fitness cost of apical dominance, or minimize apical dominance directly. This prediction was supported: all of the species compensated but none overcompensated for shoot apex removal in terms of biomass or flower production.