Germination response to light and temperature in eight annual grasses from disturbed and natural habitats of an arid Arabian desert

- Sandy desert grasses had greater dormancy, compared to those of disturbed sites.
- Grasses of natural habitats had narrower range of germination requirement.
- Grasses of disturbed sites were positively photoblastic.
- Negative photoblastism recorded only in one species at specific temperatures.

It has been hypothesized that annuals of unpredictable arid deserts produce dormant seeds as a strategy for risk spreading, but weedy annuals have lower dormancy and positively photoblastic seeds. I tested this hypothesis by comparing dormancy, and photoperiod and temperature requirements during germination in annual grasses of unpredictable arid deserts and other grasses from disturbed sites. Seeds were collected from four annual grasses of natural sandy deserts and other four from disturbed sites of an arid Arabian desert. Seeds were germinated in three incubators adjusted at daily night/day temperature regimes of three temperatures in both continuous darkness and alternating 12 h light/12 h darkness. The four sandy desert grasses had greater dormancy, compared to those of disturbed sites. Light and temperature ranges of germination were narrower and species specific for sandy desert grasses. Seeds of the grasses of disturbed sites germinated at wider range of temperatures and all were positively photoblastic, except Chloris virgata. Negative photoblastism was very rare, recorded only in seeds of Coelachyrum brevifolium at lower and moderate temperatures. Seed photoblastism depended more on habitat types than seed mass. The light and temperature requirements of the studied grasses can explain their adaptation and distribution in natural habitats.