Seed dormancy release in three common pasture grasses from a Mediterranean-type environment under contrasting conditions

Pastures in the Mediterranean region of Australia are typically comprised o f a mixture of winter annuals, including grasses and legumes, which utilise a seed bank to survive the long, dry summer. The risk of out-of-season sum mer rain requires species from such environments to adopt appropriate strat egies to protect their seed banks. The seed bank strategies of the grasses from these environments have, so far, received little attention. We conduct ed an experiment to observe the dormancy release characteristics of 3 grass es common to these environments when stored under contrasting thermal regim es. The grasses studied were great brome grass (Bromus diandrus Roth), annu al ryegrass (Lolium rigidum Gaud.), and barley grass (Hordeum leporinum Lin k). The different species displayed contrasting dormancy release characteri stics over the summer. Two of the species examined (great brome grass and a nnual ryegrass) displayed relatively late release from dormancy which gave high levels of protection from false breaks. The other (barley grass) displ ayed earlier release from dormancy which would enable it to better exploit earlier true breaks but make it more sensitive to false breaks. Unlike past ure legumes, high and fluctuating temperatures were not necessary for the s eeds of these grasses to become germinable. In fact, exposure to high tempe ratures appeared more likely to suppress release from dormancy.