Abstract:

Prairie grass （Bromus willdenowii） is a serious invasive weed escaped from sown pastures to wild grassland. To investigate factors contributing to invasiveness and ecological adaptability of prairie grass， the effects of temperature， humidity， seed burial depth， pH， salinity and osmotic potential on seed germination and emergence were examined in the laboratory. Among temperature treatments tested， it was found that the seed germination percentage was highest （92.1%） in an alternating temperature regime of 30/20 °C （day/night）. Seed germination percentage gradually decreased with decline in daily average temperature declined. There was nearly no germination when daily average temperature was close to or below 10 °C. Germination rates of seeds incubated in the pH range from 5 to 10 were all above 90%. Germination results of seeds incubated in weakly acidic or weakly alkaline conditions were significantly higher than those incubated in neutral pH. Germination rates of seeds incubated in ≤20 mmol·L^-1 NaCl were similar to those of control. Germination was above 85% for seed incubated in 160 mmol·L^-1 NaCl. The optimum osmotic potential for seed germination was -0.1 MPa. Germination rates of seeds incubated at osmotic potentials lower than -0.2 MPa were not significantly less than those of controls. Germination at an osmotic potential of -0.4 MPa was above 80%. The optimum soil relative humidity for seed germination rate and germination potential was 60%. Germination of seeds placed on the soil surface was higher than for any other burial depth. Seeds sown deeper than 10 cm did not germinate. These results indicate that seed germination of prairie grass occurs freely over a wide range of conditions， conferring a high ecological fitness. Thus， prairie grass has a high potential to invade large areas of Yunnan where the prevailing climate is warm and dry periods of below average rainfall can occur.

Key words: Bromus willdenowii, seed germination, environmental factors, ecological adaptation