THE ROLE OF APICAL DOMINANCE IN THE INTERPRETATION OF ADAPTIVE ARCHITECTURE IN PROSTRATE PLANT-SPECIES

The role of apical dominance in the interpretation of adaptive archite cture was investigated for six prostrate plant species representing a range along the 'phalanx-guerilla' continuum: Euphorbia polygonifolia, Polygonum aviculare, Trifolium repens, Glechoma hederacea, Fragaria v irginiana, and Potentilla anserina. According to the phalanx efficienc y and guerilla efficiency hypotheses, the removal of shoot apices disr upts apical dominance and increases branching, which in turn, increase s shoot interference within the plant and/or reduces foraging efficien cy. Hence, we predicted that shoot apex removal would result in an und ercompensation growth response rather than the compensation or overcom pensation commonly reported for upright species. Plant architecture wa s represented by patterns of allocation of meristems to three possible developmental fates: growth, reproduction, and inactivity. Clipping h ad no effect on architecture or fitness estimates (biomass, total numb er of meristems, and ramet production) in T. repens or G. hederacea. F itness estimates were reduced by clipping in P. anserina, but branchin g intensity was unaffected. Foraging was compromised since clipped pla nts were unable to resume horizontal extension. In E. polygonifolia, c lipping also reduced fitness estimates but without any effect on branc hing intensity. Since this species is naturally highly branched (i.e., with weak apical dominance), there may be little opportunity to incre ase branching intensity by removing apical meristems. In P. aviculare and F. virginiana, the removal of shoot apices resulted in reduced api cal dominance and increased branching intensity and this was accompani ed by reduced fitness estimates. These results suggest that apical dom inance plays an important role in determining the adaptive architectur al strategy of these latter two species.