Variations in size structure, growth and reproduction in Japanese plantain (Plantago asiatica L.) between exposed and shaded populations

Abstract

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.

Differences in plant‐size structure and biomass allocation in plants between exposed and shaded Plantago asiatica populations at a mid‐elevated habitat in the cool‐temperate region of Japan

“…The smaller matter allocation to the rhizome in the plants under the shade might be a result of the consumption of substrates accumulated in the rhizome to develop the above‐ground shoot for more effective light capture. In shaded P. asiatica plants in a lowland setting, the reduced rhizome mass from spring to summer regrows by the end of the growing season (Kobayashi et al . 2001).…”

“…In the lowlands (Mito), the leafing period is early spring to late autumn, and the plant flowers and produces seeds continuously during most of this period (Kobayashi et al . 1999; Kobayashi et al . 2001).…”

“…where we have been studying the life history and population structures of lowland P. asiatica (Okamoto et al . 1996; Kobayashi et al . 2001).…”

“…In the exposed and shaded populations, two replicate plots were set up on 20 September 1996, and two other replicate plots were set up on 30 September 1997. The two populations were assumed to have their greatest biomass in the growing season, as is the case for the lowland populations (Kobayashi et al . 2001).…”

“…In addition, in shaded environments, a greater allocation to the productive organ (leaves) has been found to maintain the growth of P. asiatica plants (cf. Kawano & Matsuo 1983; Kobayashi et al . 2001).…”