Seed germination ecology of the endemic Iberian winter annuals Iberis pectinata and Ziziphora aragonensis

The germination ecology of the winter annual Iberian endemics Iberis pectinata and Ziziphora aragonensis was investigated in order to better understand adaptations of rare species to their natural habitat and to improve ex-situ propagation techniques and management of their habitat. Specifically, we analysed the following aspects: (1) influence of temperature, light conditions and seed age on germination patterns; (2) phenology of germination; (3) germinative response of buried seeds to seasonal temperature changes; and (4) temperature requirements for induction and breaking of secondary dormancy. Germination was substantially lower in darkness than with a photoperiod in both taxa, with this difference being more pronounced in Z. aragonensis. Freshly matured seeds showed conditional physiological dormancy, germinating at low and medium temperatures but not at high temperatures (28/14 and 32/188C). Germination capability increased with time of dry storage in both species, suggesting the existence of non-deep physiological dormancy. Under greenhouse conditions, germination of both taxa was mostly concentrated in autumn (October– November), while spring percentages were less than 1% of total accumulated germination recorded during the study. I. pectinata and Z. aragonensis seeds buried and exposed to natural seasonal temperature variations in an unheated greenhouse came out of conditional dormancy in summer and re-entered it in winter, thus exhibiting an annual conditional dormancy/ non-dormancy cycle. Dormant seeds of both species which were stratified at 28/14 or 32/188C during an 8-week period, were non-dormant when they were subsequently incubated over a range of temperatures from 5 to 25/108C. Non-dormant seeds were induced into dormancy when stratified at 5 or 15/48C for 8 weeks, showing a particularly low germination response at high temperatures. Recommendations for wild-population reinforcement programmes and for the management of the natural habitat of both endemics are discussed.