Light Quality and Intensity Effects on the Germination of Species From the Jarrah (Eucalyptus marginata) Forest of Western Australia

Abstract

Eucalyptus marginata Donn. ex Sm. (jarrah) produces a canopy that reduces light intensity, but has only minimal effects on the relative proportions of particular wavelengths (light quality). Under controlled laboratory conditions, variation in light quality did not affect the germination of the representative jarrah forest species. In Eucalyptus marginata, E. calophylla Lindley, Acacia drummondii subsp. candolleana Lindley, and Kennedia prostrata R.Br., however, percentage germination under controlled laboratory conditions was greater in full darkness and seven restricted wavelength treatments than in full white light. Difference in response between full white light treatment (86 mu mol m^-2 s^-1) and the s restricted wavelength trials (2-8 μmol m^-2 s^-1) indicated a possible effect of light intensity. Compared with complete darkness and a white light intensity of 1 mu mol m^-2 s^-1, white light intensities of 26 and 146 mu mol m^-2 s^-1 reduced germination percentage in the canopy species, E. marginata, E. calophylla, and the understorey species, Acacia lateriticola Maslin, Bossiaea aquifolium Benth., Gompholobium knightianum Lindley, G. marginatum R.Br., G. tomentosum Labill. and Sphaerolobium vimineum Smith. By comparison with dark conditions, no light-inhibited germination at 146 mu mol m^-2 s^-1 was recorded for Acacia drummondii subsp. candolleana, Chorizema ilicifolium Labill., Kennedia coccinea Vent. and Xanthorrhoea gracilis Endl. An ability to sense light and remain dormant is adaptive in relation to seed burial and a subsequent increase in the survival potential of seedlings due to greater moisture availability. This light-sensing capacity was most prevalent in the small-seeded (< 10 mg) species of this Mediterranean-type climate forest. Most of the small-seeded species are likely to be buried by ants facilitated by elaiosomes or by falling into minute cavities in the gravelly soils of the jarrah forest.