Dormancy/nondormancy cycles in spores of the liverwort Sphaerocarpos texanus

The presence of a dormancy/nondormancy cycle was investigated in spores of the winter, annual, liverwort, Sphacrocarpos texanus. To test for loss of dormancy, mature laboratory-derived spores were held at three daily alternating incubation temperature regimes (thermoperiods) of 35/20, 30/15, and 25/15°C. For 22 intervals (varying from one week to 91 weeks), spores were transferred from each of these three thermoperiods onto a wet substrate in a germination chamber hem at 16/10°C. Loss of dormancy, indicated by the spores ability to germinate, increased as the length of time spores kept in the incubation thermoperiods increased. Loss of dormancy in spores hem at 35/20°C increased faster than spores held at 30/15 and 25/15°C. Spores held at each of the three thermoperiods germinated best when transferred to 16/10°C and failed to germinate when transferred to 35/20 and 30/15°C. Spores subjected to simulated seasonal temperature changes were induced back into secondary dormancy when subjected to low temperatures. The loss of dormancy and subsequent induction of dormancy suggest that S. texanus has a dormancy/nondormancy spore cycle similar to that found in seeds of obligate winter annuals.