Influence of fluctuating temperatures and H2O2 treatment on germination of Leucospermum cordifolium and Serruina florida (Proteaceae) seeds

Abstract

Seeds of Leucospermum cordifolium (Salisb. ex Knight) Fourcade and Serruria florida Knight were germinated at constant temperatures of 4, 11, 18 and 25°C and also at fluctuating temperatures that were made up of pairs of these temperatures over a 24 h period, the lower temperature of each pair being maintained for 16 h. An oxygenating treatment of soaking seeds in 1 % H2O2 resulted in a slight increase in germination of L. cordifolium seeds, without statistical interaction with temperature conditions. Diurnal temperature amplitude had the strongest effect on germination. An optimum low and high temperature of 9 and 24°C respectively was calculated for germinating seeds of L. cordifolium and 7 and 20°C for S. florida seeds. The daily surface soil temperature fluctuations recorded in burnt mesic mountain fynbos during winter was found to be of the same order as required for germination. The temperature conditions recorded in unburnt, lightly or heavily shaded soils did not meet the germination requirements. A close relationship is therefore indicated between ecological conditions and germination requirements in these two species. Sade van Leucospermum cordifolium (Salisbury ex Knight) Fourcade en Serruria florida Knight is by konstante temperature van 4, 11, 18 en 25°C en by wisselende temperature, opgemaak uit pare van hierdie temperature oor ’n 24 h periode, geïnkubeer. By wisselende temperature is die laer temperatuur vir 16 h gehandhaaf. Oksiginerende behandeling deur sade in 1% H2O2 te week het tot ’n geringe toename in kieming by L. cordifolium sade gelei, sonder statistiese wisselwerking met temperatuur-toestande. Daaglikse temperatuurskommeling het kieming die sterkste beïnvloed. ’n Optimum lae en hoë temperatuur van 9 en 24°C respektiewelik is vir kiemende sade van L. cordifolium bereken en 7 en 20°C vir sade van S. florida. Die daaglikse wisseling in oppervlakgrondtemperature, gemeet in gebrande mesiese bergfynbos, was gedurende die winter van dieselfde orde as dié benodig vir kieming. Temperatuur-toestande gemeet in nie-gebrande, lig- of swaar-beskadude grond het nie aan die temperatuurvereistes voldoen nie. ’n Noue verband bestaan dus tussen ekologiese toestande en kiemingvereistes by hierdie twee spesies.