This week, we welcome our own Jenna Finley. As stated in the previous post, EEB seminars will be run through Zoom.
Time: Mar 26, 2020 12:30 PM Eastern Time (US and Canada)
Meeting ID: 857 735 992
Do species with strong apical dominance incur a cost in terms of suppressed potential fecundity or biomass?
Abstract: Plants typically allocate axillary meristems to one of three principal fates: branching / growth (G), reproduction (R), or inactivity (I). The latter is commonly enforced (temporarily or permanently) by ‘apical dominance’, promoting a growth form that favours vertical shoot extension — mediated by the effects of auxin produced in the shoot apical meristem. When the latter is removed however (e.g. by consumers), meristem allocation may change, thus affecting plant architecture, biomass accumulation, and/or reproductive effort. Fecundity and/or plant mass may consequently suffer (under-compensation), remain unaffected (compensation; tolerance), or may increase (overcompensation). The latter thus signifies a ‘cost of apical dominance’, but one that may be outweighed by several potential benefits from having apical dominance intact; e.g. tall stature and thus avoidance of shading effects from neighbouring plants. I removed the shoot apical meristem for replicate plants early in the growing season within natural populations of 22 herbaceous angiosperm species with a conspicuously vertical (‘main stem’) growth form, commonly found in eastern Ontario — to: (i) test for a cost of apical dominance; (ii) examine effects of removal on leaf size and leafing intensity (number of leaves per unit stem dry mass) ; and (iii) explore effects of between-species variation in leafing intensity on propensity for a cost of apical dominance. Clipped and unclipped (control) plants had their near neighbours removed, and were harvested after seasonal flowering production had virtually finished but before seed dispersal. Dry mass was measured separately for above-ground body size (vegetative stems), leaves, seeds, and fruit; and counts were recorded for each type of meristem, number of leaves, fruits, and seeds per plant. I predicted that: (i) species with a strong apically-dominant growth form would respond to shoot apical meristem removal with greater branching intensity, and thus over-compensation in terms of fecundity and/or biomass (displaying a cost for apical dominance); and (ii) overcompensation is enabled by production of more but smaller leaves, and hence with a larger bank of axillary meristems (per unit stem dry mass) available for deployment in branching and/or flower/fruit production. Widely variable compensatory capacities were recorded for the study species, suggesting probably effects of uncontrolled between-species variation in phenology, life history traits, and natural susceptibility to herbivory. I also found no significant between-species relationships for compensatory response versus mean leaf size or leafing intensity. Overall, the results point to species-specific treatment effects on meristem allocation patterns, and no generalized ‘cost of apical dominance’ in herbaceous plants.