Effects of temperature, light and gibberellic acid on the germination of seeds of 43 species native to Western Australia

Abstract

Abstract. Species native to the southwest of Western Australia, representing a range of plant families, life‐history strategies, fire‐response syndromes, seed‐store types and seed weights, were tested for viability using tetrazolium chloride and for germination under combinations of constant temperatures of 15 °C or 23 °C, constantly dark or 12 h diurnal whitelight conditions, and with, or without, addition of gibberellic acid (GA3, 50 mg/l). Species previously known to require a heat‐shock treatment to overcome dormancy due to an impervious testa were pre‐treated prior to imposition of temperature, light and GA3 conditions. The test environmental conditions related to differences between winter and autumn temperatures and surface and buried seed germination positions of post‐fire habitats. The viability of the selection of native Western Australian species ranged from 0 to 100 %, averaging 71 %. For all taxa, no combination of temperature, light and gibberellic acid treatment induced all viable seeds to germinate. The greatest percentage germination achieved in any combination of treatments averaged 71 % of all viable seeds for all species. Larger seeds (> 10 mg seed weight) tended to have greater viability percentages, but no overall patterns of viability or germinability were attributable to seed storage syndrome, strategy of fire recovery response or life‐form type. Germination of most of the dominant tree representatives (Eucalyptus calophylla, E. diversicolor, E. erythrocorys, E. gomphocephala, and E. patens) was indifferent to the trial conditions of temperature, light and GA3. However, Eucalyptus marginata showed reduced germination in the light, which was overcome with GA3. GA3 also overcame the inhibition resulting from exposure to light in some understorey species (e.g. Allocasuarina campestris, Regelia ciliata, Xanthorrhoea gracilis and X. preissii). Germination of many hard‐seeded, understorey shrub and herbaceous perennial species, especially those with small (< 10 mg) seeds (e.g. Bossiaea ornata, B. aquifolium and Acacia drummondii ssp. candolleana) was greater at the lower trial temperature and in the dark. Some large (> 10 mg) seeded, understorey species (e.g. Acacia extensa, Kennedia coccinea, K. prostrata, Hovea trisperma and Hardenbergia comptoniana) germinated in high percentages in both temperatures, but maximum germination percentages still tended to be at 15 °C. Large‐seeded species were less sensitive to exposure to light compared to the smaller seeded species. The largest seeded species tested, Paraserianthes lophantha, germinated best in the warmer incubation temperature and in the light. The ecological significance of the tests would be that species which have seed dormancy mechanisms capable of delaying germination until the cool temperature, winter rainy period of this mediterranean‐type climate would be more likely to survive than if germination followed summer rain showers or the first, intermittent rains of autumn. Burial of seeds becomes more important if germination occurs when...

Probability of germination after heat treatment of native Spanish pines

“…This fact suggests that pine adaptation to perturbations must be sustained not in dormancy characteristics or structural properties that prevent immediate germination of seeds as is usual in Mediterranean plants [7,8,24,56], but in other adaptive responses.…”

Effects of temperature, light and other treatments on seed germination of Leymus chinensis

“…Seeds of species having a requirement for temperature fluctuation are much more likely to have dormancy enforced on them than seeds of species without such a requirement, in view of the relatively small amplitude of diurnal fluctuations of soil temperature that occurs beneath an established sward (Thompson et al 1977). Bell et al (1995) suggested that the ability to detect light is a mechanism that allows seed to discern between the buried and the unburied state. As significant quantities of light rarely penetrate greater than 5 mm of soil surface (Tester and Morris 1987), L. chinensis seeds that experience light condition and germinate would probably be on the soil surface in natural environments.…”

Seed-based approach for identifying flora at risk from climate warming

“…Consequently, mechanisms that minimize the risk will be under strong selection pressure (Meyer et al 1997), with natural selection favouring seed germination patterns that increase the probability of successful seedling establishment. For example, although temperature is not considered to be a limiting factor for recruitment in Mediterranean-type ecosystems (Lloret et al 2004), germination generally coincides with early winter when temperatures are low (typically 10-15°C; Bell 1999) and rainfall is reliable (Mott 1972;Bellairs & Bell 1990;Bell & Bellairs 1992;Bell et al 1995). This maximizes the period of root development prior to summer drought, thereby increasing seedling survival (Bell 1999).…”