Flooding effects on the amphicarpic seed production of Persicaria thunbergii and differences of two seed types in early life stage

Abstract

To better understand the amphicarpy of Persicaria thunbergii as the reproductive strategy in stressful environment, I investigated the effects of flooding on the amphicarpic seed production and compared seed size and seedling stress response using a mesocosm experiment. First, I observed the effects of flooding on the amphicarpic seed production of P. thunbergii. To konw the effect of the timing of the simple flooding, plant were submerged at a depth of 30cm during 2 weeks in June and August, respectively. To mimic severe damages by the flooding, 50% of the leaves were removed and the plants were shaded for 1 week in the late vegetative growth period (August). The results showed that the simple flooding in the both periods had no effects on the production of the amphicarpic seeds and the vegetative parts. However, the flooding with the damages tended to decrease the production of the seeds and the biomass. In particular, the production and the one seed weight of the subterranean seed were significantly decreased with the biomass reduction under the strong disturbance. Also, the subterranean seeds were formed later than the aerial seeds. I can suggest that unlike other amphicarpic plants, P. thunbergii may not produce the subterranean seeds according to a pessimistic strategy and can reduce the production of the subterranean seeds when time and energy do not permit. The amphicarpy as evolutionary adaptations for P. thunbergii can have different ecological significance than for other amphicarpic plants. Second, I compared aerial and subterranean seeds and seedlings in size, weight, and seedling stress response. The major axis and minor axis of the subterranean seeds were 22% and 17% longer than that of the aerial seeds, respectively. The subterranean seeds were 39% heavier than that of the aerial seeds. In the control group, the average stem length of the SS (seedling from subterranean seed) was 41% longer than that of the SA (seedling from aerial seed). Also, SS preponderated in leaf number, root length and overall dry weight over SA. In shaded group, the SS had 34% longer stem length and 99% wider leaf area than SA. Moreover, SS could grow stem length more rapidly to escape the water level than SA. The cause of producing superior subterranean seeds can be one of the strategies to survive in a negative environment in early life history. By producing not only the aerial seeds for dispersion but also subterranean seeds for survival, the P. thunbergii, which inhabit extreme riparian areas, seems to leave behind a community at its mother-site.