Seed biology and ex situ storage behaviour of Australian Nymphaea (water lilies): implications for conservation

    Research output: ThesisDoctoral Thesis

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    Abstract

    [Truncated] The iconic, basal angiosperm genus Nymphaea (Nymphaeaceae) occupy many of the world’s freshwater wetlands, with 18 species occurring in northern Australia. Generally, our knowledge of wetland plant species is limited, and even more so for species occurring in the monsoonally driven wet-dry tropics of northern Australia. In order to guide the management and conservation of Nymphaea in Australia, this thesis seeks to improve our understanding of these charismatic plants, and presents the first detailed investigation into the seed biology of the genus.

    Investigations into the seed dormancy of Australian Nymphaea revealed that five species underwent embryo growth prior to radicle emergence, and were thus classified as having morphophysiological dormancy (MPD). This finding adds to the increasing body of literature suggesting MPD is basal within the angiosperms. Additionally, all study species showed a requirement for light, and maximal germination occurred in a small temperature window between 30-35 °C. A phenomenon previously reported in the literature that crowding seeds under flooded conditions was observed, and produced high germination in all species of Nymphaea tested in this study, when incubated under optimal temperature and light conditions. This response, termed ‘crowding’ was attributed to the endogenous production and concentration of ethylene by the seeds, which acts as a germination stimulant.

    As all species displayed specific germination requirements, I further investigated how dormancy may be naturally overcome under natural conditions, and tested treatments that can be applied to break dormancy ex situ. I found that dormancy loss under simulated natural conditions occurs in conjunction with increasing (over-night) temperatures at the onset of the summer wet season, when seeds are permanently inundated with water. However, when tested under laboratory conditions, temperature alone did not break dormancy. Cycles of wetting and drying, used to mimic the sporadic rainfall of northern Australia, acted to completely alleviate dormancy in seeds of one species (N. lukei), in conjunction with the exogenous application of ethylene. Under simulated burial conditions, seeds were found to be semi-persistent, and can remain viable in dry soils for > 12 months. However, viability rapidly declined when under simulated wetting and drying cycles.

    Original languageEnglish
    QualificationDoctor of Philosophy
    Supervisors/Advisors
    • Dixon, Kingsley, Supervisor
    • Merritt, David, Supervisor
    • Tuckett, Renee, Supervisor
    Publication statusUnpublished - 2016

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