Original paper

Effect of drying, salinity and temperature on seed germination of the submersed wetland monocot, Vallisneria australis

Salter, Jacqueline; Morris, Kay; Read, Jenny; Boon, Paul I.

Abstract

Periods of low water level ('drawdown') may kill mature submersed aquatic plants and their vegetative propagules. Re-establishment from a sediment-based seed bank may be limited by desiccation, high temperatures and increased salinity, environmental changes that may often accompany drawdown. Vallisneria australis (Hydrocharitaceae) is a common, submersed clonal wetland plant in southeastern Australia, which reportedly reproduces mainly by vegetative spread. Although vegetative growth in this species is inhibited by drying and salinity, it is not known how such conditions influence the germination of sediment-stored seed, and so whether re-colonisation from seeds can occur after drawdown. Hence, this study examined whether drying, high temperature or high salinity reduced the germination of V. australis seeds. Germination was slowed by drying, with significant germination still occurring 20-30 weeks after re-wetting. The final percentage germination of seeds that had been dried for 8, 16 or 32 weeks and then rewetted was approximately twice that of seeds that remained wet. Moreover, sediment-stored seeds germinated only after drying, suggesting that drawdown would promote germination of V. australis in the field. Final germination of wet-stored seeds was 44 % at 25 °C but only 7 % at 35 °C, indicating that germination may be inhibited over summer in southeastern Australian wetlands. Although percentage germination declined with increasing salinity, some seeds still germinated (∼10 %) at the highest salinity tested, 23 dS m-1. Variability in the time V. australis seeds take to germinate may represent a mechanism that increases the opportunities for regeneration in an unpredictable environment. The demonstrated tolerance of seeds to drying and salinity suggests that, even in salinised wetlands, V. australis may be able to recolonise from the sediment-based seed bank following the loss of mature plants after a drawdown, provided viable seeds are present.

Keywords

wetlandwater regimerehabilitationsubmersedpropagule banksdroughtdrought recoveryregenerative strategiesmacrophyte