An experimental device for studying seed responses to naturally fluctuating temperature of surface soil under a constant water table

1. A simple experimental device was designed, in which seeds can be exposed to natural fluctuation of surface soil temperature under a constant soil moisture condition maintained by an automatic water supply system based on the principle of a Mariotte siphon. 2, Except for the period during summer drought, surface soil temperature at a depth of 5 cm and its fluctuation within the device were largely similar to the temperature of the surface soil subjected to natural fluctuation of moisture. 3. The seeds of Persicaria lapathifolia placed at the depth of 0 5 cm in the soil within the device germinated during the natural germination season of the species, while the seeds placed at the depth of 5 cm or beneath the 10 cm-thick layer of litter failed to germinate. 4. The ungerminated seeds retrieved in August did not germinate at the favourable alternating temperature in the laboratory test unless exposed to previous moist chilling, suggesting the induction of secondary dormancy. Therefore, higher summer temperatures but not summer drought or moisture fluctuation seem to have been responsible for the dormancy induction, because the dormancy was induced in the fully hydrated seeds.