No abstract

Groups of dry seeds of four annual plant species which occur in the Negev highlands were placed on a natural, dry or wet loess soil crust surface near Sede Boker on the Zin plateau during the autumn before the first rains, and on the first day with rain (1.15 mm). Ant nests ofMessor rugosuswere 8 to 14m from the experimental plot. The length of time it took these ants to collect the free or adhered seeds was observed. When the mucilaginous ombrohydrochoric seeds ofAnastatatica hierochuntica, Plantago coronopus, andCarrichtera annuaadhere to wet soil that remains moist, most of the seeds may have time to germinate in proper conditions before they are collected by ants. However, all but 5% of theReboudia pinnataseeds were collected within 2 h. The adhered seeds that had been moistened by wet soil crust and then dried, were collected by ants, in most cases, faster than when seeds and soil remained moist. Within 2 h none of the dry and free seeds situated on the dry soil surface remained. The first free seeds were collected after 7 min. Findings are discussed together with the mechanisms and strategies involved in seed dispersal by rain and germination of these plant species.

Plantago coronopus var. crassipes is a common annual plant in many areas of the Negev Desert highlands. The dry seed coat cross section and surface structure of P. coronopus seeds before the first wetting were examined by SEM, as were the freeze-dried mucilage and adhesion of the seeds to the soil crust. When wetted, the mucilaginous layer forms, and seeds on the soil surface adhere to the soil crust. Some P. coronopus mucilaginous seeds may be dispersed by rain, even after less then 10 min of wetting. The dry seeds can float on run-on water for 10–44 min and are then dispersed along runnels into depressions, or adhere within a few minutes to the wet soil crust near the dry mother plant. Seeds matured on dry plants in a natural habitat in spring 1995, germinated in December 1995 to 96% after 72 h at 20 °C in light, but only to 2% in dark. The importance of mucilaginous seeds for the survival of the plant species under desert conditions is discussed.

No abstract

No abstract