The purpose of the research presented in this dissertation was to determine the degree of salt tolerance and the life history characters of a perennial halophyte Limonium stocksii (Boiss.) Kuntz. during germination and growth. Seeds of L. stocksii were collected from a population located near Hawks Bay at the Arabian sea, Karachi. Seed germination of L. stocksii was studied under controlled conditions in the laboratory at two light levels (12 h light/I 2 h dark and 24 h dark), two salinity sources (NaCl and seawater) with six concentrations (0, 10, 20, 30, 40, 50 and 60 dS m-1), four temperature regimes (fluctuating night/day temperature regimes of 10/20, 15/25, 20/30, 25/35°C) and eight germination regulating chemicals (kinetin, GA, proline, betain, ethephon, nitrate, thiourea and Na-hypochlorite) using a completely randomized block design. Maximum seed germination of L. stocksii was obtained in non-saline control at all temperature regimes, however, 20/30°C appeared to be the optimal temperature where maximum germination was recorded up to 20 dS mol NaCI. Seawater inhibited seed germination more than NaCI at low and moderate temperatures but H the highest temperature regime (25/35°C) seed germination in seawater was more than NaCI. Absence of light had little effect under non-saline condition, whereas, addition of salinity highly inhibited seed germination in dark and this inhibition was higher in seawater. Rate of germination was higher in all non saline solutions and increase in NaCI and seawater salinity decreased the rate of germination. Rate of germination was low in the cooler temperature regime and an increase in temperature gradually increased rate of germination. Higher germination rates in NaCl solution occured at 20/30°C while in seawater at 25/35°C. Seeds when transferred to distilled water after 20 d of either NaCI or seawater treatments recovered completely. Na-hypochlorite was identified as a successful germination alleviating compound for salinity and temperature induced dormancy. Kinetin and ethephon partially alleviated salinity enforced seed dormancy in both light and dark conditions while other chemicals had no significant effect.
Salinity tolerance experiments of Limonium stocksii were conducted under ambient conditions. Plants were grown from seeds in plastic pots containing sandy soil and sub-irrigated with 0, 10, 20, 30, 40, 50 and 60 dS m-1 solutions of both NaCI and seawater. Plants grown in non-saline control and in 10 dS m-I of both NaCI and seawater showed maximum growth (plant height, fresh and dry weight). Increasing salinity from 20 to 60 dS m-I led to growth inhibition. Tissue water content remained unaffected with increase in both NaCI and seawater salinity. Limonium stocksii accumulated considerable amounts of Na+ and C1 in comparison to K+, Ca2+ and Mg2+ with increasing salinity. Na+ accumulated more in stem than leaf and root. The selective ion transport capacity of stem was higher and was maximum for Na +.
Seed bank and demography of L. stocksii population were studied for one year. Three transects (300 ft. each) were laid across the population from landward to seaward zones. Soil pH of the study site ranged from 8.1 to 8.5 while soil conductivity varied from 55 dS m-1 to 191 dS m-1. The over all seed density was highest (5,887 seeds m-2) in May and lowest in June. Seed density was highest in the landward zone and declined towards the seaward zone. Little variation was observed in different growth parameters throughout the year. Plant tissue water was lower in zones with high soil salinity. Leaves showed comparatively higher tissue water content from January to March. Al growth parameters such as number of branches, root length, stem length and biomass were highest in the intermediate zone. Na+ C1- accumulated more in leaves and stem than in roots while Mg2+ and Ca2+ were high only in leaves. K+ levels were similar in all parts of L. stocksii. Ion accumulation (except Ca2+) was more in intermediate zone in comparison to landward and seaward zones.