Plant dispersal strategies, seed bank distribution and germination of Negev Desert species.

In a natural flat area of deep loess soil in the Negev Desert of Israel, near Sede Boker, the distribution of seeds of different species, in the seed bank, is a result of their strategies of seed dispersal, seed size and structure and seed germination. Samples were collected in summer from 39 plots measuring 350cm(2). In Carrichtera annua (L.) DC., which has a protection strategy, seeds are enclosed in lignified structures as aerial seed banks on the dry and lignified plant until they are dispersed by rain. Of 3244 C. annua seeds, 3110 were found in the aerial seed bank. In Spergularia diandra (Guss.) Heldr. & Sart., which has an escape strategy, the tiny dust-like mature seeds are dispersed into cracks in the soil by wind. Of 1043 seeds, 896 were found in the upper 0-1 cut layer of soil and only 99 at a depth of 1-2 cm. No seeds remained on the dry plants. Neotorularia torulosa (Desf.) Hedge & J. Leonard has developed a dual dispersal strategy. Of 954 N. torulosa seeds, 630 were found protected in the aerial seed bank. The rest were dispersed by wind, 177 escaped into the upper 0-1 cm layer of soil and 147 were at a depth of 1-2 cm.