Comparison of Thermal and Hydrotime Requirements for Seed Germination of Seven Stipa Species From Cool and Warm Habitats

Temperature and water potential are two important environmental factors influencing germination and subsequent seedling establishment. Seed germination requirements vary with species and with the environment in which the seeds are produced. Stipa species dominate large areas of the Eurasian zonal vegetation, but comparisons of germination requirements between Stipa species from different habitats is limited. We investigated the effects of temperature and water potential on seed germination of S. grandis, S. purpurea, and S. penicillata from habitats with low temperatures and relatively abundant rainfall (cool habitats) and S. glareosa, S. breviflora, S. gobiea, and S. bungeana from habitats with relatively high temperatures and low amount of rainfall (warm habitats). Seeds of species from cool habitats had a higher base (T_b), optimal (T_o), and maximum (T_c) temperature than those of species from warm habitats, except for the base temperature of S. purpurea. Response of six tested Stipa species to water potential differed among species but not between habitats. Median water potential for germination was lowest for S. bungeana, S. penicillata, and S. gobiea. There was a negative correlation between hydrotime constant (θ_H) and base water potential for 50% of the seeds of all species to germinate (ψ_b(50)). Germination time of seven Stipa species in response to temperature and water was well predicted by thermal time and hydrotime models. Results of the present study on germination of these seven species of Stipa may provide useful suggestions for grassland restoration in different habitats.