Germination of two halophytes: Halopeplis perfoliata and Limonium axillare from Saudi Arabia

Abstract

Halopeplis perfoliata and Limonium axillare are perennial halophytes. The distribution of the former is north and south Hijaz, that of the latter includes north and south Hijaz, the northern and eastern regions of Saudi Arabia and Al-Rub Al-Khali. The two species are important components of the littoral salt marsh vegetation of the Red Sea coast. Where they occur together, as in the Rabigh salt marsh, H. perfoliata occupies the moister zone while L. axillare inhabits a zone further inland. The salt content is considerably higher in the H. perfoliata zone than in that of L. axillare. Experiments showed that the germination temperature responses of non-dormant seeds of the two species were broadly similar: they germinated over a wide range of constant temperatures (H. perfoliata, 5–35 °C and L. axillare, 5–40 °C) and also at various fluctuating temperature regimes simulating temperature cycles that prevail during both the rainy and dry seasons. Seeds were also germinated at varying salinity levels (2305·5, 4611, 9222·5, 18,445, 27,667 and 46,112 p.p.m. = 5, 10, 20, 40, 60 and 100 per cent, respectively of seawater) and temperatures fluctuating between 32 and 10 °C, and 40 and 23 °C. The salt tolerance of the seeds of the two species was considerably lower than the salt content in the soil samples (0–5 cm depth) within the habitats of the species. Although the seeds of H. perfoliata at 32–10 °C exhibited a higher salt tolerance than those of L. axillare, both species germinated rapidly to comparable high percentages at 2305·5, 4611 and 9222·5 p.p.m. Increasing the incubation temperature decreased the range of salt tolerance as well as rates of germination, particularly in L. axillare. The inhibition of germination of the seeds of both species by salinities beyond their tolerance is due to the high osmotic potential of the medium. The ecological significance of the responses of the seeds to the various environmental variables is discussed.