Comparison of the effects of temperature and water potential on seed germination of Fabaceae species from desert and subalpine grassland

Temperature and water potential for germination based on the thermal and hydrotime models have been successfully applied in predicting germination requirements of physiologically dormant seeds as well as nondormant seeds. However, comparative studies of the germination requirements of physically dormant seeds from different ecosystems have not been done.Germination of scarified seeds of four legume species collected from the Qing-Tibetan Plateau and of four collected in the Alax Desert in China was compared over a range of temperatures and water potentials based on thermal time and hydrotime models.Seeds of species from the Qing-Tibetan Plateau had a lower base temperature (T b) and optimal temperature (T o) for germination than those from the Alax Desert. Seeds of the four species from the Qing-Tibetan Plateau germinated to high percentages at 5°C, whereas none of the four desert species did so. Seeds of species from the Alax Desert germinated to a high percentage at 35°C or 40°C, while no seeds of species from the Qing-Tibetan Plateau germinated at 35°C or 40°C. The base median water potential [Ψ b(50)] differed among species but not between the two habitats.The thermal time and hydrotime models accurately predicted the germination time course of scarified seeds of most of the eight species in response to temperature and water potential; thus, they can be useful tools in comparative studies on germination of seeds with physical dormancy. Habitat temperatures but not rainfall is closely related to germination requirements of these species.