The role of apical dominance in the interpretation of adaptive architecture in prostrate plant species
The role of apical dominance in the interpretation of adaptative architecture was investigated for six prostrate plant species representing a range along the 'phalanx-guerilla' continuum: Euphorbia polygonifolia, Polygonum aviculare, Trifolium repens, Glechoma hederacea, Fragaria virginiana, and Potentilla anserina. According to the phalanx efficiency and guerilla efficiency hypotheses, the removal of shoot apices disrupts apical dominance and increases branching, which in turn, increases shoot interference within the plant and/or reduces foraging efficiency. Hence, we predicted that shoot apex removal would result in an undercompensation growth response rather than the compensation or overcompensation commonly reported for upright species. Plant architecture was represented by patterns of allocation of meristems to the three possible developmental fates: growth, reproduction, and inactivity. Clipping had no effect on architecture or fitness estimates (biomass, total number or meristems, and ramet production) in T. repens or G. hederacea. Fitness estimates were reduced by clipping in P. anserina, but branching intensity was unaffected. Foraging was compromised since clipped plants were unable to resume horizontal extension. In E. polygonifolia, clipping also reduced fitness estimates but without any effect on branching intensity. since this species is naturally highly branched (i.e. with weak apical dominance), there may be little opportunity to increase branching intensity by removing apical meristems. In P. aviculare and F. virginiana, the removal of shoot apices resulted in reduced apical dominance and increased branching intensity and this was accompanied by reduced fitness estimates. These results suggest that apical dominance plays an important role in determining the adaptative architectural strategy of these latter two species.
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