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Germination depth vs. temperature requirements in naturally dispersed seeds of Leucospermum cordifolium and L. cuneiforme (Proteaceae)

1987; Elsevier BV; Volume: 53; Issue: 2 Linguagem: Africâner

10.1016/s0254-6299(16)31445-4

1727-9321

G.J. Brits,

Botany and Plant Ecology Studies

Myrmecochory (ant dispersal) and the requirement for both low and high diurnal soil temperatures during seed germination after fire, are important ecological determinants in the seedling recruitment phase of Leucospermum R. Br. species. A crucial unknown parameter linking these two factors is the effective burial depth (i.e. germination depth) of seeds stored in the subterranean seed bank. The germination depth of seedlings was effectively determined in a nursery trial by measuring the length of the hypocotyl between the radicle end and ground level. Using this method the germination depth of Leucospermum cordifolium (Salisb. ex Knight) Fourcade and L. cuneiforme (Burm. f.) Rourke seedlings emerging during winter, after summer burns in three localities was estimated. Average estimated germination depths varied between 30 and 45 mm. Daily minimum and maximum temperatures were measured at various soil depths during winter in burnt and unburnt mesic mountain fynbos. Temperatures measured at 10, 20 and 40 mm depths during winter were close to the known optimum daily low and high germination temperatures in L. cordifolium, in burnt fynbos, but not in unburnt fynbos. These temperatures in burnt fynbos prevailed especially during early winter. It was concluded that a high proportion of the Leucospermum cordifolium seed bank will germinate only during the first early winter following a fire. Other aspects of natural seed dispersal were studied. These included seedling dispersal numbers and patterns around burnt mother plants. Evidence for seed dispersal and burial by ants was found. Mierverspreiding van sade, asook die vereiste vir lae en hoë daaglikse grondtemperature gedurende kieming na ’n brand, is belangrike ekologiese determinante in die saad-regenerasie fase van Leucospermum R. Br. spesies. ’n Belangrike onbekende parameter wat hierdie faktore koppel, is die effektiewe diepte waarop sade begrawe word, d.i. die kiemingdiepte van sade wat in die ondergrondse saadbank geberg word. Die kiemingdiepte van saailinge is doeltreffend bepaal, in ’n kwekery-studie, deur die lengte van die hipokotiel tussen die kiemwortelkant en die grondoppervlak te meet. Met behulp van hierdie metode is die kiemingdiepte beraam van Leucospermum cordifolium (Salisb. ex Knight) Fourcade en L. cuneiforme (Burm. f.) Rourke saailinge, wat in die winter ná somerbrande opgekom het in drie lokaliteite. Gemiddelde kiemingdieptes het gewissel van 30 tot 45 mm. Daaglikse minimum en maksimum temperature is op variërende gronddieptes gedurende die winter in gebrande en ongebrande mesiese berg-fynbos gemeet. Temperature wat op 10, 20 en 40-mm diepte gemeet is in die winter, was na aan die optimum daaglikse lae en hoë kiemingtemperature vir L. cordifolium, in gebrande fynbos, maar nie in ongebrande fynbos nie. Hierdie temperature in gebrande fynbos het veral gedurende die vroeë winter geheers. Die afleiding is gemaak dat ’n hoë proporsie van die Leucospermum cordifolium-saadbank sal ontkiem slegs gedurende die eerste vroeë winter wat volg na ’n brand. Ander aspekte van natuurlike saadverspreiding is bestudeer. Dit het die verspreidingsgetalle en -patrone van saailinge om verbrande moederplante ingesluit. Getuienis dat sade deur miere versprei en begrawe word, is gevind.