Seed germination requirements of four emergent macrophytes in North Queensland

[Extract] INTRODUCTION It has been claimed that the seed from some aquatic species (e.g. Nelumbo nucifera, the sacred lotus) can last from one to three thousand years, on evidence recovered from peat under drained lakes of the Pulantien basin of South Manchuria (Bewley and Black 1982). More realistically, using modern carbon dating techniques, this may actually only be 200-300 years (Hanson 1973). However, it is clear that some plant seeds can remain viable for extended periods, given favourable conditions for dormancy. Dormancy optimises the distribution of germination in time or space, such that it limits the appearance of new plants to times which are advantageous, eg. after low temperatures have passed or when there is sufficient moisture, light etc. \ud \ud It is generally recognised that seeds in wetlands can form persistent seed banks which will endure seasonal environmental variations in light intensity, moisture level and diurnal temperature (Leck and Simpson, 1987; Welling et al., 1988; Baskin et al. 1989, 1993 and Smits et al. 1990). These reports suggest that if water is non-limiting, seeds may only require suitable temperature regimes and adequate light to overcome dormancy. That is, many wetland species have seed banks which can be regarded as "nondormant" (Baskin et al. 1989).\ud \ud Much of northern Australia is considered to be in the wet-dry tropics, and it is characterised by a strongly aseasonal climate. That is, although rainfall is seasonal (often December-March), it is sporadic, with the rainfall pattern being unpredictable and its distribution governed mostly by monsoonal events. Hence, the 'traditional seasonality' of temperature and light intensity seen in temperate climates (where the majority of studies have been conducted) is much less pronounced in northern Australia. Seed dormancy may be dependent, among other factors, on oxygen and water availability as well as light and temperature conditions. \ud \ud There are limited studies on the role of seed dormancy mechanisms in the maintenance and regeneration of northern Australian wetlands. Information about the mode of germination, establishment and reproduction of wetland macrophytes are needed, as our knowledge remains incomplete and rudimentary. This is now recognised as a serious problem, as many land-use practices, such as land clearing for agriculture and urbanisation, has led to the degradation and loss of traditional wetland areas. Active management of wetlands will be necessary to maintain, restore and revegetate degraded areas. Similarly, the development of suitable practices for artificial wetland management is required. Many constructed wetlands provide little habitat value and/or host a variety of aquatic weeds. Methods for the seed propagation of native emergent aquatic macrophytes are required for the rehabilitation and construction of wetlands.\ud \ud To fill this gap, pilot experiments were undertaken to determine which environmental factors were affecting the germination of various wetland seeds. All of the study species chosen were typically distributed along margins and banks of stationary or slow-moving water bodies, swamps, and channels in tropical Australia. As such, they would be considered useful in wetland restoration and management. Aquatic macrophytes were targeted which were either threatened by land use practices, for example Eleocharis dulcis, or have potential for use in artificial wetlands for wastewater treatment, such as Phragmites karka and Schoenoplectus validus.\ud \ud Little is known about the methods used to propagate collected seed or the optimal conditions for germination. Therefore, given the climate of north Australia, it was considered important that the storage method for collected seeds be assessed (dry storage vs wet/buried storage) and that the effect of the germination environment also be assessed (oxygen vs anoxia and light vs dark). All seeds were trialed under constant temperature and moisture conditions