Effects of nutrient availability on the amphicarpic traits of Persicaria thunbergii

Abstract

Environmental factors affecting the expression of amphicarpic traits in Persicaria thunbergii are not well studied. We thus performed to investigate the effects of nutrients on the amphicarpic traits of P. thunbergii in a mesocosm experiment. Three nutrient levels were applied using different intervals between fertilization: no fertilization (low nutrient), fertilization at eight-week intervals (medium), and at four-week intervals (high). We compared the relative stem length growth rates (RGRST) and biomass allocation of seedlings from aerial seeds (SA) and subterranean seeds (SS), and then investigated the flowering time and the seed production traits of P. thunbergii according to nutrient level. The results showed that RGRST, biomass allocation and total biomass were not different between SA and SS at all levels. Aerial flowering started earlier than subterranean flowering, in contrast to other amphicarpic plants. Subterranean seed allocation and the number of subterranean seeds were stable regardless of nutrient levels whereas aerial seed allocation decreased with increasing nutrient level. The number of aerial seeds per biomass with low nutrient was significantly higher than that at other levels. P. thunbergii showed a different trait of seed production: subterranean seeds appeared to play a role in retaining the mother-site while aerial seeds can escape the site conditions at low nutrient levels. In conclusion, the reproductive strategy of P. thunbergii on aerial propagule was changeable but not subterranean propagule under various nutrient conditions. SA and SS were similar about growth responses. Those characteristics would increase survivability of P. thunbergii. Evolutionary drivers might explain the differences of life-history strategies in flowering time between the aquatic P. thunbergii and other arid amphicarpic plants.