Seed Dormancy And Germination Characteristics Of Stipa Bungeana Trin

Seeds of Stipa bungeana Trin., a dominated perennial grass on the Loess Plateau, were used in present study. The characteristics of seed dormancy, seed germination response to environmental factors, such as light, temperature, moisture, salinity, nitrogen compounds, and burial depth were determined. Further, survival of soil seed bank and seedling recruitment in the field was investigated. The main results are as follows:1. Germination percentage of fresh seeds was low at several combinations of light and temperature. The highest germination percentage was25%in darkness at20℃. In addition to at15/25℃,20/30℃, no seeds germinated at the other temperatures. These results suggest fresh seeds of S. bungeana have primary dormancy.2. Storage temperature and time had significant effect on seed dormancy release of Stipa bungeana. Percentage of seed germination increased as dry storage time increasing. For example, seeds stored at20℃for1,3,6months germinated to46%,59%and69%, respectively. High temperature favored seed dormancy release. Seeds stored at5℃and20℃for6months germinated to63%and69%in dark, respectively.3. Light, temperature and their interactions had significant effect on germination of nondormant seeds. Germination percentage increased and then declined with the increase of temperature. The optimum temperature for germination is20℃in which seeds germinated to88%and75%in dark and light conditions, respectively. Light significantly reduced germination of S. bungeana seeds regardless of temperature. For example, seed germinated to86%and48%at15℃in dark and in light, respectively.4. Water stress, light, and their interactions significantly influenced seed germination. Germination percentage decreased with water stress increased. Inhibition of water stress on germination becomes more in light. For example, seed germination percentage was0and15%in light and in dark at-0.8MPa water potential.5. KNO3and NaNO3significantly improved seed germination in light. For example, KNO3and NaNO3increased germination percentage from34%to45%and59%, respectively at15℃. However, KNO3had no significant promoted effect on germination at low temperature (20℃、15℃) in dark, and even significantly inhibited germination at high temperature (25℃). E.g. germination percentage was reduced from40%to6%in dark at25℃by KNO3.6. Seedling emergence increased and then decreased with the increase of sowing depth. The highest emergence percentage was43%when sown at a depth of1cm.7. Seedlings mainly recruited during7-9months. Consistent with this, the density of soil seed bank peak in August and then declined.8. More than90%seeds germinated or lost viability after burial for three months in the field. After one year burial, all seeds lost viability at a depth of5cm and4%seeds on soil surface remained viable. These results suggest seeds of S. bungeana mostly have transient soil seed bank.