On the ecology of Zygophyllum aegyptium in Egypt

Abstract

Zygophyllum aegyptium A. Hosny sp. nov. (Fam. Zygophyllaceae) is a closely related taxon to Z. album, but can be differentiated by the flowering branches and during fruiting stage. It is distributed in the Mediterranean region of Egypt, Tunis and Cyprus. As a taxon of the genus Zygophyllum in Egypt, Z. aegyptium is ecologically interesting. The species has broad ecological amplitude where it can grow in different habitat types. Z. aegyptium plays an important role in the zonation pattern of the vegetation in the Deltaic coast of Egypt. The zonation usually beings at the coast with a zone of Z. aegyptium community type which builds up sand mounds forming a narrow belt of vegetation runs parallel to the coast.

Seeds were collected from individuals growing in three habitats namely: salt marshes, sand dunes and fertile, non-cultivated lands. The seeds were tested for germination in the laboratory under different conditions. The following results were obtained.

• (1) At constant temperatures, seeds from the sand dune habitat germinated over a wide range, from 5–45° C, whereas seeds from the fertile, non-cultivated land germinated over a temperature range from 10–40° C. The seeds from the salt marsh exhibited an intermediate behaviour between sand dune and fertile, non-cultivated land. The optimum germination temperature for the three groups of seeds was around 25°C. Germination at alternating temperatures was better than the average germination at constant temperatures. The highest average cumulative germination was obtained at alternating temperatures of 20 night/30°C day, with a percentage of 67% for seeds from sand dunes, 40% for fertile, non-cultivated lands, and 79% for salt marsh seeds.

• (2) In response to light, seeds from the fertile, non-cultivated lands showed no response to the variation of light/dark treatments. Seeds of the salt marsh plants attained the highest germination percentage in the dark, while alternating light/dark promoted the seed germination of the sand dune seeds.

• (3) Germination of seeds decreased with the decrease of water potential. The reduction of germination was greater for seeds of fertile, non-cultivated land than seeds of the salt marsh which germinated over osmotic potential range from 0–16 bars. Seeds of the sand dune showed an intermediate germinability in the order of -12 bars.

• (4) For the effect of pH value, fertile land seeds showed the best germination at pH of 7, while seeds of the sand dune attained broad optimum germinability over pH range from 7–9. Meanwhile, the salt marsh seeds occupied an intermediate optimum germination of pH 7–8.

• (5) The optimum depth of sowing was found to be 0.5 cm. At shallow depths from 0–1cm, seeds of the salt marsh showed higher germinability than the other types of seeds. The reverse was true at sowing depths of 2–2.5 cm. In contrast, seeds of the sand dunes exhibited an opposite behaviour with better germination at sowing depth of 1.5–3.5 cm than the other two types of seeds.