Flooding effects on seed production of the amphicarpic plant Persicaria thunbergii

• Flooding can reduce the amphicarpic seed production in Persicaria thunbergii.
• Subterranean seeds of P. thunbergii are formed later than the aerial seeds.
• Subterranean seeds of P. thunbergii are more vulnerable to flooding disturbance.
• The amphicarpy of P. thunbergii can have different ecological significance.

The purpose of the study was to investigate the effects of flooding on amphicarpic seed production of Persicaria thunbergii using a mesocosm experiment. The plants were subjected to 2 weeks of inundation corresponding to plant height in June and August to assess the effect of simple flood timing. To mimic severe damage caused by flooding, 50% of the leaves were removed and the plants were shaded for 1 week. The results showed that simple flooding during early vegetative growth and the late vegetative growth had no effects on production of amphicarpic seeds or vegetative parts. The amphicarpic seeds of P. thunbergii did not show any changes under inundation levels reaching plant height. However, flooding with damage during late vegetative growth tended to decrease the production of subterranean seeds and total plant mass. In particular, production and single seed weight of subterranean seeds decreased significantly with a reduction in biomass under a strong disturbance. Subterranean seeds were formed later than aerial seeds. We suggest that unlike other amphicarpic plants, subterranean seeds of P. thunbergii are vulnerable to poor environmental conditions and the plant reduces production of subterranean seeds when time and energy do not permit. Amphicarpy, as an evolutionary adaptation by P. thunbergii, seems to have different ecological significance from that of other amphicarpic plants.