Plantago asiatica is a perennial herb that is distributed over a wide range of east Eurasia. The population structure, growth and reproduction in exposed (E-) and shaded (S-) populations of P. asiatica were examined in the Kanto District of eastern Japan. In both populations, the plant size structure showed a bimodal distribution during spring to early summer, in which the two modes corresponded to smaller seedlings and larger overwintered plants, respectively. In autumn, this distribution became unimodal due to seedling growth. However, this change occurred later in the S-population because of suppressed growth in the seedlings. In the S-population, flowering also began later in the growing season and the threshold plant size for flowering was larger than that of the E-population. Biomass allocation to the rhizomes was greater in autumn in the reproductive plants of the S-population. Growth and biomass allocation in plants grown from seeds collected from each population were compared under phytotron conditions. Near a saturated photon flux density, E-population plants had a higher relative growth rate than S-population plants. Therefore, E-population plants should allocate resources to reproductive organs sooner. Shaded population plants were not vigorous in their growth and reproduction. Seed size (dry weight per grain) was significantly greater in the Spopulation than in the E-population, both in the field and under phytotron conditions. These results suggest that ecotypic differentiation in life-history strategies, which is mainly due to light availability, occurs among local P. asiatica populations. The effects of severe trampling on early reproduction in the E-population are also discussed.
Plantago asiatica L. (Plantaginaceae) is a perennial herb that is distributed over a wide range of habitats from exposed to shaded sites in lowlands to the subalpine zone in Japan. We investigated the patterns of biomass allocation and population structures based on the frequency distribution of individual plants in order to clarify the extent of plasticity in significant life-history traits and also population dynamics of this plantain species, which occurs under two contrasting light regimes-in exposed and shaded habitats-at Numappara, 1230 m a.s.l., Tochigi Prefecture, central Honshu. The plants at the shaded site allocated more biomass to leaves, but less to rhizomes than those at the exposed site. Increasing the biomass of the reproductive organs resulted in a reduction of the leaf and rhizome fractions. This trend is clearer in the shaded plants than in the exposed plants. In both exposed and shaded populations, the number of seedlings was greater in the first year, but the population structure was skewed more negatively in the second year during two consecutive study years. The possible effects of allocation traits of individuals on the population structures and regeneration mechanisms of P. asiatica at elevated habitats are discussed in terms of cyclic changes in population structure with the fluctuations of seeding activity over some years.
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