Temperature effects on dormancy release and germination rate in Sorghum halepense (L.) Pers. seeds: a quantitative analysis

Seed dormancy in Sorghum halepense is overcome by exposure to fluctuating temperatures and the effect is determined both by the diurnal amplitude and the maximum temperature. It was found that repeated cycles of particular regimes were additive, each cycle resulting in release from dormancy of a further proportion of the population. The range of regimes having this additive effect was wider in seeds which had after-ripened in the soil during winter than in those which were freshly dispersed. The temperature-dependent germination rate of seeds whose dormancy had been removed by the effect of fluctuating temperatures was analysed using a ‘thermal time’ approach, and estimates obtained of base and optimum temperatures and the required ‘thermal time’ for the germination of different fractions of the population. The results provide a basis for developing a model to predict seedling recruitment in the field using soil temperature data.