The small leafy succulent shrub Halocnemum strobilaceum occurs in saline habitats from northern Africa and Mediterranean Europe to western Asia, and it is a dominant species in salt deserts such as those of north-west China. Seeds that did not germinate in the NaCl solutions were tested for germination in deionized water.
Seeds from which radicles had barely emerged in deionized water were transferred to NaCl solutions for 10 d and then back to deionized water for 10 d to test for radicle growth and recovery.
Seeds germinated to higher percentages in light than in darkness and at high than at low temperatures. Seeds that did not germinate in NaCl solutions did so after transfer to deionized water. The seed and early seedling growth stages of the life cycle of H. Plants can be divided into two broad groups with respect to salt tolerance: halophytes salt tolerant and glycophytes salt intolerant.
Halophytes can grow and complete their life cycle in saline environments, whereas glycophytes cannot Ungar, The responses of seeds of halophytes to salt differ from those of non-halophytes. Thus, compared with glycophytes, seeds of halophytes germinate at higher salinities, and they maintain viability even under extreme salinity or osmotic stress, recovering and germinating when the water potential of the medium increases Ungar, Germination of halophytes in the field is controlled by several environmental factors, in particular light Gutterman, ; Huang and Gutterman, , a , temperature Badger and Ungar, and salinity Ungar, ; Khan et al.
Seeds of four species required light for germination, four germinated to higher percentages in light than in dark, 13 germinated equally well in light and dark, and two germinated to higher percentages in dark than in light.
Halophyte species vary in their tolerance to salinity during seed germination Ungar, ; Khan et al. Seeds of halophytes can recover the capacity to germinate after exposure to salt stress that inhibits their germination Woodell, Further, following pre-treatment of seeds of halophytes with salt solutions, the rate and percentage of germination often increase after they are transferred to fresh water Katembe et al.
Halocnemum strobilaceum Chenopodiaceae occurs in saline habitats from northern Africa and Mediterranean Europe to western Asia Liu, In China, this species is distributed mainly in the north-west provinces of Xinjiang and Gansu. It is an ecologically important semi-shrub in saline soils on the plain in front of the south slopes of Tianshan Mountain, Xinjiang.
In this area, H. In highly saline patches or on shores of salt lakes, H.
In slightly saline habitats, it is commonly found in association with other species such as Halostachys caspica Chenopodiaceae , Tamarix hispida , T. They can even survive in soil covered by a 5—10 cm layer of salt crust Wu, Although the effect of salinity on seed germination of H. Most importantly, different ecotypes of the same species occurring in different habitats may have different adaptation strategies to the special environmental conditions during seed germination and seedling growth in their local sites.
To this end, the present study investigated the seed germination ecophysiology of H. Seeds of H. The embryo is fully developed and located in a peripheral position, rarely encircling the endosperm. Thus, the type of seed produced by H. Mature seeds were collected in November , from plants of H.
This area is a temperate inland desert in the hinterland of the Eurasian continent. The site has typical desert vegetation, alkali-saline grey desert soil and a continental climate.
Salts accumulate on the soil surface in the dry season; however, salt concentration is diluted by water from melting snow in spring and by rain in summer Li, Soil samples collected from ten randomly chosen areas within the study population of H.
Another reason for considering only NaCl is that apparently it is the major component of salinity in the deserts of north-west China Fan et al. Seeds were incubated in 50 mm diameter Petri dishes on three layers of Whatman No.
Petri dishes were sealed by plastic film to prevent evaporation. Germination in the light was monitored every 24 h, at which time germinated seeds were counted and removed from the Petri dishes. After 15 d, when no additional seeds had germinated for 5 d, experiments in light were terminated, and seed germination in darkness was checked first and only at this time.
Germination was monitored every 24 h, and germinated seeds were counted and removed from the dishes. Final germination percentages were calculated after incubation for 15 d. Ungerminated seeds from the 15 d NaCl pre-treatments were rinsed three times in deionized water and then incubated in deionized water.
Seed germination recovery was monitored every 24 h, at which time germinated seeds were counted and removed from the dishes.
Final germination recovery percentages were calculated after 15 d of incubation using the following formula:. Seedling incubation was terminated after 10 d and mean radicle length recorded.
Then, seedlings incubated in different NaCl concentrations for 10 d were rinsed three times with deionized water and transferred to filter paper saturated with deionized water for an additional 10 d, at which time final radicle lengths of the seedlings were measured.
Effect of temperature and light on germination of Halocnemum strobilaceum seeds after 15 d of incubation in deionized water. Different upper case letters indicate significant differences in germination percentage across the range of temperatures for seeds incubated in the light and for those incubated in the dark, and different lower case letters indicate significant differences between seeds incubated in the light and darkness at a given temperature.
Two-way ANOVA analysis of effects of temperature, light and their interactions on seed germination of Halocnemum strobilaceum.
Effects of NaCl on germination and its recovery in deionized water of seeds of Halocnemum strobilaceum. Values followed by the same letter do not differ significantly. Radicle growth recovered after seedlings were transferred to deionized water. However, elongation recovery decreased with the increase in pre-treatment salinities. Radicle elongation recovery in Halocnemum strobilaceum after transfer from different concentrations of NaCl to deionized water.
In the life cycle of a plant, seeds have the highest resistance to extreme environmental stresses, whereas seedlings are most susceptible, and this is especially true for desert species Gutterman, Therefore, successful establishment of a plant population is dependent on the adaptive aspects of seed germination and of early seedling growth. Germination of many halophytes occurs when the combination of photoperiod, temperature regime, soil water and soil salinity is optimal for plant growth Naidoo and Naicker, ; Gutterman, ; Zia and Khan, Thus, for example, seeds of perennial plants in the Artemisietum herbae-albae plant community type of the Negev Desert, Israel, germinate en masse only once in several years Evenari and Gutterman, Germination percentages of H.
This characteristic of H. The light requirement for germination of H. If buried at soil depths to which light cannot penetrate, they may become part of a persistent soil seed bank. Song et al.
In which case, the seeds of H. This could explain why seeds of H. These responses are similar to those of seeds of some salt marsh and salt desert species, i. In north-west China, seeds of H.
In the field, seeds of this species germinate primarily from April to July. In this summer rainy season, rainwater washes away salts on the soil surface and at shallow depths. Thus, seeds heretofore prevented from germinating can germinate under this optimal combination of low salinity, high soil moisture and high temperatures.
The ability of seeds of H.
Halophyte seeds respond to salinity in two ways: a germination is inhibited by high salinity, but seeds do not lose their viability; and b salinity stress delays germination but does not induce dormancy or kill the seeds Ungar, , ; Levitt, However, seeds of Salicornia pacifica var.
Although germination of H. Cold stratification caused a significant increase in germination of H. In general, the difference between germination percentages of seeds at low salinities and that in deionized water is insignificant, but they gradually decrease with further increase of salinity Khan and Ungar, ; Katembe et al. Seeds of most halophytes exposed to salinities that inhibit germination will recover and germinate after they are transferred to distilled water.
Effect of temperature on seed germination pdf
Further, final germination percentages are even increased by salt pre-treatment in most species Khan and Ungar, ; Gul and Weber, ; Khan et al. For example, seeds of Allenrolfea occidentalis recovered to germinate rapidly and to high percentages after they were transferred from high salinity solutions to distilled water Gul and Weber, However, seed germination of some species is permanently inhibited by high salinity.
For instance, seeds of Zygophyllum simplex Zygophyllaceae could hardly recover to germinate after they were transferred from a high salinity solution to distilled water Khan and Ungar, In the present experiments, ungerminated seeds of H. Thus, seeds of H.
Wu reported that plants of H. They even can survive in soil covered by a 5—10 cm layer of salt crust.
★ Seeds That Germinate at 30°f - 40°f Temperature (Sowing Seeds & Sprouting Times)
Seedlings of halophytes can develop in solutions with low concentrations of salts; however, radicle growth may be greatly retarded by high salinity Malcolm et al. As expected, growth of H. These physiological responses are similar to those of Annona muricata and A. Tobe et al.
However, young roots of H. Thus, for successful establishment of H. During the rainy season in spring and summer, the salinity on the soil surface would be decreased by precipitation, and then seeds could germinate successfully and seedlings become established.
In the desert area near the Dead Sea, seedlings of Mesembryanthemum nodiflorum Aizoaceae appear in the winter, only after several rains, which dilute the salt accumulated during the summer from the upper layer of the soil.
Germination of seeds of H. Germination recovered rapidly after seeds of H.
Growth of seedlings of H. Thus, tolerance to salinity of seedlings from southeastern Spain apparently is higher than that of those from north-west China. In north-west China, H. The ability of H. When salinity is high in the dry season, seeds do not germinate, but they do germinate when salinity is diluted by precipitation.