Vernal pools in the southwest Australian floristic region: biogeography, seed dormancy, germination and storage

Renee Tuckett

    Research output: ThesisDoctoral Thesis

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    Abstract

    [Truncated abstract] Vernal pools (a form of temporary wetland) of the Southwest Australian Floristic Region (SWAFR) are rich in species and endemism. There are two types of vernal pool in the SWAFR, claypans and gnammas, each with their own specialist and cosmopolitan species. Both types of vernal pool are subject to a number of localised and global threats. This is the first detailed study on the flora of claypans and gnammas in the SWAFR bringing together both biogeography and seed biology to provide practitioners the knowledge to effectively conserve the plant species occurring in these ecosystems. Biogeographical surveying of gnammas throughout the SWAFR showed that gnammas have one of the highest levels of plant endemism for any ecosystem in the SWAFR. However, species richness was not correlated with any of the environmental or morphological parameters measured. Pockets of richness were identified and found to be scattered throughout the region. I show that the drivers of species richness for gnammas differ to those of the terrestrial flora of the SWAFR and to those of the claypans. The lack of correlations and absence of shared genera between gnammas and the flora from surrounding ecosystems suggest that gnammas species have originated via long-distance dispersal attributing to the random mosaic of pools with high species richness. Germination and dormancy of seeds from claypans and gnamma species is variable with seed from some species being dormant and those from others not. While non-dormant seeds were able to germinate over a range of temperatures, temperatures upon which germination was highest was species-specific. Seeds from some species, including members of the Hydatellaceae, an early divergent angiosperm, had a germination temperature preference of 5-10 °C, lower than that previously been recorded for Australian aquatic species. In fact, for aquatic plant species worldwide, temperature preferences for germination below 15 °C are uncommon. A light preference or requirement for germination was a significant variable for all species thus I conclude that maintaining the integrity of the soil crust may be an important first step for on-site conservation of vernal pool and gnamma species. A particular focus of the thesis is the Hydatellaceae, a group of tiny annual aquatic plants that have undergone recent taxonomic realignment to the base of the angiosperm phylogenetic tree. The Hydatellaceae are important for developing our understanding of the processes of evolution in early angiosperms. I observed a type of germination, whereby the embryo differentiates outside of the seed coat, that heretofore has not been reported and thus assign a new type of specialised morphophysiological dormancy to these primitive plants. Evolution of embryo types and desiccation tolerance is also discussed in light of presented results. Ex situ storage of seeds in facilities such as seed banks is a cost effective and efficient method of plant genome conservation. Seed storage theory predicts that as storage temperature and moisture content of seeds decrease (with some limitations) the longevity of orthodox (desiccation-tolerant) seeds can be extended...
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2010

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