Environmental factors controlling seed germination and seedling recruitment of Stipa bungeana on the Loess Plateau of northwestern China

Germination studies are important for collecting information on field seedling recruitment, plant conservation and restoration. This study investigated the role of light, temperature, nitrogen, water stress and burial depth in controlling germination of Stipa bungeana seeds. S. bungeana seeds are photo-inhibited; light significantly decreased seed germination regardless of temperature and water conditions. Seeds germinated at 10–30° C, and the highest germination was 72 % and 88 % at 20° C in light and dark, respectively. Thermal model analysis showed that presence of light significantly increased average thermal requirement θ _T (50)] from 105°Cd to 186°Cd at sub-optimal temperature, implying that light delays seed germination. Hydrotime model analysis showed that presence of light caused a shift in the median base water potential Ψ _b(50)] from ?0.68 to ?0.26 MPa, which partly explains why light decreased both percentage and speed of germination, even at optimal conditions. As burial depth increased, seedling emergence initially increased and then decreased; the highest seedling emergence recruitment was 43 %, for seeds buried at a depth of 1 cm. Field observations showed that seedling emergence occurred primarily from July to September, and scarcely occurred from April to June. These results suggest that the light inhibitory effect is an adaptive mechanism that prevents S. bungeana seeds from germinating on the soil surface. To attain highest seedling establishment, seeds of S. bungeana should be sown at a soil depth of 1 cm prior to the rainy season, using seeds stored for 1 year.