Seed germination inLaunaea arborescens: a continuously flowering semi-desert shrub

doi:10.1006/jare.1996.0201

Journal of Arid Environments

Volume 36, Issue 1, May 1997, Pages 113-122

https://doi.org/10.1006/jare.1996.0201 Get rights and content

Abstract

Achenes (seeds) of the perennial shrubLaunaea arborescens(Asteraceae) germinated under a wide range of environmental conditions. None of the seeds were dormant, nor was there any evidence that dormancy could be induced. Apparently, this semi-desert species has no means of preventing immediate germination. Achenes are produced and dispersed throughout the year, and we suggest that the timing of germination is regulated by the duration and degree of wetting and the presence of moderate soil temperatures. This germination behaviour suggests that there is no mechanism by which the germination of seeds formed one year can be delayed until subsequent years. By contrast, most desert plants accumulate persistent seed banks. The germination strategy ofL. arborescensmust be considered opportunistic, and we suggest that the survival of populations is ensured by other life history traits like continuous iteroparity and effective dispersal by wind.

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We conducted experiments on seed germination, seedling survival and seedling growth of four Eucalyptus species to identify factors that might explain why they are restricted to the two major soil types in southwestern Australia, deep sands (E. macrocarpa, E. tetragona) and lateritic loam (E. loxophleba, E. wandoo). At high temperatures (28 °C), germination in darkness was lower for the two ‘loam species’ than for the ‘sand species’, while there were no differences in light or at low temperatures (10 °C). Germination commenced earlier, and was faster in the sand species than in the loam species, but was almost inhibited in all species by –1.0 MPa. E. tetragona proved the most drought-tolerant in terms of germination level and seedling survival. Seedlings of the sand species had much longer roots two weeks after germination in the absence of water stress, and the roots of more seedlings continued to elongate under moderate water stress (–1.0 MPa), than the two loam species. Roots were longer in all species, except E. macrocarpa, at –0.5 MPa than at –0.1 MPa, despite seedlings having a smaller mass and hypocotyl length. As water availability declined, there was a tendency for the sand species to survive longer on sand than on loam while soil type had no effect on the loam species. Pattern and duration of seedling survival of the loam species was similar to that of the sand species despite their smaller seeds. We conclude that seedlings from the large-seeded sand species are able to penetrate the soil profile faster and deeper, but that they are not less prone to drying soils than seedlings from the small-seeded loam species. Instead, seed size and germination speed are important prerequisites to cope successfully with unstable soil surfaces and to exploit the rapidly descending water in deep sands.
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^☆: White, J.

^f1: Present address: School of Environmental Biology, Curtin University of Technology, GPO Box U1987, Perth WA 6001, Australia.

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Regular ArticleSeed germination inLaunaea arborescens: a continuously flowering semi-desert shrub☆

Abstract

Life cycle ecology of annual plant species of cedar glades of southeastern United States

The Population Structure of Vegetation

Germination ecophysiology of herbaceous plant species in a temperate region

American Journal of Botany

Afterripening pattern during cold stratification of achenes of ten perennial Asteraceae from eastern North America, and evolutionary implication

Plant Species Biology

Germination response patterns during dormancy loss in achenes of six perennial Asteraceae from Texas, USA

Plant Species Biology

Eco-physiological studies on desert plants. II. Germination ofZygophyllum coccineum

Oecologia

Studies of halophytes. I. The germination of the seed and establishment of the seedlings of five species ofAtriplex

Ecology

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

Journal of Vegetation Science

El Clima de la Provincia de Almeria

An incubator for studies of germination responses to temperature and interacting environmental factors

Seed Science and Technology

The effect of soil water potential on seed germination of some British plants

New Phytologist

The effects of the parent environment on seed germinability

Seed Science Research

Die natürliche Vegetation des südostspanischen Trockengebiets

Botanische Jahrbücher

Do the germination mechanisms differ in plants originating in deserts receiving winter or summer rain?

Israel Journal of Botany

Seed Germination in Desert Plants

Strategies of seed dispersal and germination in plants inhabiting deserts

Botanical Review

Regular Article
Seed germination inLaunaea arborescens: a continuously flowering semi-desert shrub☆