Factors Affecting Seed Germination in Three Annual Species from an Arid Region of Western Australia

TLDR: In this article, Mott et al. investigated the role of seed surface characteristics in modifying the seed/soil interface and found that a greater area was better suited for germination under high moisture tensions.

Abstract: Since arid regions are usually zones in which rain falls in sporadic heavy showers, plant growth is limited to the periods of high soil moisture content following these showers (e.g. see Koller 1969). Annual plants must complete their life cycle during these periods, so that mechanisms which ensure the successful germination and establishment of annuals during favourable moisture conditions are important in the survival of the annual community. In the arid Murchison Region of Western Australia (annual rainfall <200 mm), the bimodal pattern of annual rainfall leads to the development of both summer and winter annual floras (Mott 1972a, 1973). In these communities seed is evident on the soil surface throughout the year, and germination takes place on the soil/air interface (Mott 1973). The three species dominating the annual floras are the summer grass Aristida contorta F. Muell., and the two winter composites Helipterum craspedioides W.V. Fitzg. and Helichrysum cassinianum Gaud. Both Aristida contorta and Helipterum craspedioides have an obligate requirement for light at germination (Mott 1972a). Little viable seed of these species remains after any rainfall sufficient to result in germination (Mott 1973), and so the factors controlling germination are critical to the survival of the annual communities in this area. Even in moist environments the conditions for germination are more severe on the surface than for buried seed (Meeklah 1958; Evans, Eckert & Kay 1967). This can be explained by the rapid fluctuations in moisture and humidity in the micro-environment at the soil/air interface, which result in unfavourable conditions for germination (Miller & Perry 1968; Dowling, Clements & McWilliam 1971). The possibility of litter modifying soil surface conditions has also been investigated by these workers and it appears that litter cover favours seedling establishment by increasing the humidity in the microenvironment surrounding the seed. The importance of seed surface characteristics in modifying the seed/soil interface has been emphasized by Sedgley (1963) and Harper & Benton (1966). These workers showed that germination was enhanced when a greater area was in contact with the substrate, and that mucilaginous seeds showed the greatest germination under high moisture tensions. Other studies have shown that artificial water absorbent coatings increase germination of pasture plants when humidity in the micro-environment is high, due to more efficient