Plasticity and allometry of meristem allocation in response to density in three annual plants with different architectures

An experiment was conducted to investigate plasticity of meristem allocation under intraspecific competition in three annual species ( Xanthium sibiricum Patrin., Datura stramonium L., and Fagopyrum esculentum Moench.) with different architectures (monopodial, false dichotomous, and sympodial branching, respectively). There were two density treatments for X. sibiricum and D. stramonium, with plant–plant distances of 7 and 14 cm, and five density treatments for F. esculentum, with plant–plant distances of 5, 10, 15, 20, and 25 cm. We recorded meristem fates (inactive, growth, and reproduction) at several developmental stages and at the final developmental stage. Allocation of meristems to reproduction in all three species could be explained by allometric growth (“apparent plasticity”), but meristem allocation patterns to the other functions differed among the species. Allocation of meristems to growth affects and is affected by plant architecture. Our results suggest that vegetative growth is more plastic than reproduction in annual plants.

Meristem allocation and life-history evolution in herbaceous plants

Generalisations of life histories in plants are often framed in terms of allocation to reproduction. For example, relative allocation to reproduction is commonly found to be higher in semelparous than in iteroparous plant species. However, the association between vegetative traits and life history has been largely unexplored. In higher plants, reproductive and vegetative function can be measured in terms of meristem allocation. Under this approach, two vegetative traits (apical dominance (the suppression of axillary meristem development) and branching intensity (the commitment of axillary meristems to branches)) can be measured as well as one reproductive trait (reproductive effort). We used phylogenetically independent contrasts to compare reproductive and vegetative function in annual semelparous and perennial iteroparous species. Twenty congeneric species pairs (each species pair represented by one semelparous and one iteroparous species) across nine families were selected based on availability of herbarium specimens. Semelparous life-history evolution was associated with higher reproductive effort. Conversely, iteroparous life-history evolution was associated with higher apical dominance. Branching intensity was not associated with life history. An evolutionary association between life history and apical dominance but not branching intensity suggests a complex relationship between allocation to vegetative traits and the evolution of plant strategies across environments.