Abstract
Eremophila is an Australian genus of 212 species ranging from prostrate shrubs to small trees, the great majority of which occur in Western Australia. Recent interest in the genus’s germination strategies developed out of a need to seek rehabilitation techniques for mine-site and rangeland areas. The genus is of special interest because of its broad geographic range and prominence in vegetation associations of the arid zone, especially in Western Australia, where it often dominates or codominates over wide areas.
ManyEremophila species are known to be tolerant of drought, fire, frost, grazing, and salinity, and would be very suitable for revegetation programmes; however, the genus germinates poorly, for reasons that are not fully understood.
During the early 1980s attempts were made, with limited success, to rehabilitate open-cut mine-site waste dumps at Mt. Newman using broadcast seed and rooted cuttings and transplanted seedlings at the Pilbara mine venture at Paraburdoo. Tissue culture and grafting have also been attempted, but environmental management acknowledges that the broadcast seed method is the only cost-effective means of mine-site rehabilitation.
Under field conditions the germination ofEremophila occurs in response to heavy rain in autumn and winter, especially with milder temperatures; however, up until now the use ofEremophila in rehabilitation practices has been limited because of the high percentage of seeds that fail to germinate.
Two causes for this have been postulated. First, the environmental conditions may not be appropriate for germination. Physical dormancy resulting from the hard woody fruits may be overcome by using a scarification pre-treatment. Second, seed may still fail to germinate even though favourable conditions exist; a secondary chemical mechanism in the form of inhibitors associated with the fruit wall is hypothesised. Chemical properties of the seed, seed coat, or fruit may regulate germination until the fruit wall has been effectively worn away and the chemicals leached out.
Few experimental procedures have been carried out to verify these hypotheses, and few studies have examined either fruit productivity (seeds per fruit) or seed viability.
Eremophila fruit are dry with a papery exocarp or drupaceous with a fleshy or succulent mesocarp and a woody or crustaceous endocarp and contain between 2 and 12 seeds. Seed viability inE. maculata ranges from 74% to 92% in the first 3 years after fruit maturity, decreasing markedly to 8% after 13 years. Similar patterns have been recorded forE. goodwinii.
Effective environmental management utilisingEremophila may be approached in three ways. First, scarify fruit to promote the uptake of water and oxygen; second, use fruit between 1 and 5 years to ensure the highest viability rating; and third, collect fruit from healthy shrubs showing no evidence of insect or fungal attack to ensure quality of fruit.
Further research on the genus should include ecological studies, currently poorly understood, and edaphic and soil amelioration projects (e.g., on post mine-site tailings) in an attempt to optimise the vegetation potential ofEremophila.
Abstrakt
Die australische PflanzengattungEremophila (Familie Myoporaceae) weist 212 Arten auf, für die ausschließlich Holzpflanzen bekannt sind. Die meisten Arten kommen in Westaustralien vor. Das Interesse an dem Keimverhalten der Samen dieser Gattung hat sich während der letzten Jahre verstärkt, da verschiedene Arten in die Wiederbegrünung ehemaliger Tagebaugruben und gestörter ökosysteme in der Trockenzone einbezogen werden sollen. Die Anpflanzung vonEremophila ist besonders erstrebenswert, da die Arten eine weite geographische Verbreitung aufweisen, in den Pflanzengesellschaften der Trockenzone (Halbwüsten und Wüsten) in Westaustralien vorherrschen und lange Trockenperioden, Feuer, Frost und hohe Bodensalzkonzentrationen widerstehen.
Die Keimung vonEremophila Samen hat sich jedoch als schwierig erwiesen. Samen vonEremophila wurden in früheren Gruben bei Mt. Newman (Westaustralien) gesät, sowie Ableger und Sämlinge in der Pilbara Grube in Paraburdoo (Westaustralien) angepflanzt. Diese Versuche sind jedoch grötenteils erfolglos gewesen. Gewebskultur sowie Pfropfung können ebenfalls angewendet werden, aber die preiswerteste Methode ist das Säen von Samen.
Wenige Untersuchungen haben sich mit der Frucht- und Samenproduktion vonEremophila beschäftigt. Die Frucht vonEremophila ist entweder trocken mit einem papierähnlichen Exokarp oder eher durch ein fleischiges Mesokarp und einem holzigen oder krustenartigem Endokarp charakterisiert und enthält zwischen 2 und 12 Samen. Die Keimungsfähigkeit schwankt von 74% noch 92% fur 1–3 jährigeE. maculata Samen, aber beträgt nur noch 8% für 13 jährige Samen. Einen ähnlichen Einflu des Alters auf die Keimfähigkieit der Samen ist fürE. goodwini bekannt.
Die Kontrollmechanismen, die der Keimung vonEremophila Samen unterliegen, sind nur unvollständig bekannt. Mehrere Hypothesen sind bezüglich der Keimung vonEremophila Samen aufgestellt worden. Erstens könnten die Umweltbedingungen nicht geeignet sein um eine vollständige Keimung aller keimfähigen Samen zu erlauben (im natürlichen Habitat setzt die Samenkeimung nach starken Regenfällen und besonders bei milden Temperaturen, im Herbst oder Winter ein). Zweitens könnte die Fruchtwand eine mechanische Samenruhe induzeren, und Skarifizieren der
Fruchtwand könnte diese Samenruhe brechen. Drittens wäre die Samenruhe das Ergebnis chemischer Hemmstoffe, die in der Testa, dem Embryo oder- und der Fruchtwand gelagert sein könnten. Die chemischen Eigenschaften des Embryos, der Testa und-oder der Fruchtwand würden die Keimung bis zu dem Zeitpunkt regulieren, an dem die Fruchtwand abgenutzt und die Inhibitoren ausgelaugt wären.
Das Anpflanzen vonEremophila Arten könnte daher auf dreierlei Art und Weise erleichtert und gefördert werden. Die Frucht sollte skarifiziert werden um eine rasche Aufnahme von Wasser und Sauerstoff in den Samen zu ermöglichen. Die Früchte sollten nicht älter als 5 Jahre sein um beste Keimfähigkeit zu gewährleisten, und die Früchte sollten von gesunden Pflanzen gesammelt werden.
Zukünftige Forschungsprogramme sollten ökologische Studien sowie Untersuchungen zu den Bodenfaktoren, die das Wachstum vonEremophila Arten fördern, einbeziehen.
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Richmond, G.S., Chinnock, R.J. Seed germination of the Australian desert shrubEremophila (Myoporaceae). Bot. Rev 60, 483–503 (1994). https://doi.org/10.1007/BF02857928
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DOI: https://doi.org/10.1007/BF02857928