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

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 24h period, the lower temperature of each pair being maintained for 16h. 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