The effects of temperature and water availability on the germination of Bromus rubens

Background/Question/Methods

The invasion of red brome (Bromus rubens L.), a winter annual, is altering fire regimes in desert ecosystems in the southwestern USA. In this study, the primary objective was to determine the environmental conditions (temperature and water potential) that best stimulate germination in this exotic species. A laboratory study was conducted to compare germination ratios of red brome seed under gradients of water availability and temperature to better predict how climate conditions are likely to affect fire potential. Samples were prepared using different solutions of polyethylene glycol (0, -0.5, -1, -1.5, -2 bar). These samples were then placed in incubators at six temperature settings (0, 5, 10, 20, 25, 30°C) for a 28 day period during which seed germination was scored.

Results/Conclusions

Red brome seed exhibited optimum germination patterns from 10-20°C, while showing an increase in the amount of time taken to germinate in the extreme temperatures (0, 5, 25, 30°C). The water potentials at which the seeds germinated ranged from 0 to -1.5 bars and the effects of water potential were temperature dependent. In the mid-range temperatures (10-20 °C) the seeds germinated successfully (100%) from 0 to -1.5 bars. The extreme temperatures of 0 and 30°C led to germination only at 0 bars. Germination was inhibited for -2 bars at all temperatures. Our results indicate that red brome germinates most successfully within a range of 10-20°C, and anywhere from 0 to -1.5 bars. It can be expected that in a fall season of above average precipitation, if the average temperatures remain mild, optimal germination rates are likely to result in high fine fuel loads that will increase the probability of fire.