reported for the first time in any Indian plant species from our laboratory (Table 4) [29]. The fast germi-
nation indicates that these halophytes show an adaptive strategy, as the availability of water with reduced
NaCl content in soil during the rainy season exists for a short period. This is because evaporation of mois-
ture under bright sunlight and heat increases the salt content by capillary movement [29].
Ungar [102] studied the ecology of halophyte seed banks and found that in unpredictable environ-
ments not all of the seeds germinate. In inland areas seed banks may be large, but some coastal seed banks
may be very large and others small. Because annuals have only one chance to reproduce, the seed bank
for annuals may be more significant than for perennials. Several studies have indicated that seeds of gly-
cophytes and halophytes respond in a similar manner to increased salinity stress in relation to both a re-
duction in the total number of seeds germinating and a delay in the initiation of the germination process
and that seeds of many halophytes remain dormant because of low water potentials [8,103]. The success
of annual halophyte populations is greatly dependent on the germination responses of their seeds. Seed
germination usually occurs early in the growing season or during a period when soil salinity levels are re-
duced, allowing the establishment of seedlings prior to the period of highest salt stress [80].
A significant characteristic of halophyte seeds, which distinguishes them from the glycophytes, is
their ability to maintain seed viability for extended periods of time during exposure to hypersaline condi-
tions and then to initiate germination when the salinity stress is reduced [8,104,105]. The enforced dor-
mancy response of halophyte seeds to saline conditions is of selective advantage to plants growing in
highly saline habitats. These seeds could withstand high salinity stress and provide a viable seed bank for
recruitment of new individuals. However, the seed germination would be limited to periods when the soil
salinity levels were within the species tolerance limits [104].
Storage of seeds in the soil is a significant factor in recruitment of the plant population in some saline
habitats because their establishment is often difficult as their edaphic conditions are continuously chang-
ing [80,106]. One-year-old seeds of Atriplex nummulariagerminated better than freshly harvested seeds
[107]. Although several researchers have determined that a large seed bank of viable seeds does exist in
many saline habitats, it is not clear how seeds from the individual species respond to high salinity over
time [10,108].
Various reports [109,110] indicate that the source from which seeds were obtained may be very crit-
ical in determining their germination response when exposed to saline conditions. A very distinct feature
of the present study was that the seeds of different sites exhibited different behavior toward a particular
salt solution. It was also observed that the levels of salt tolerance vary within the different populations of
seeds. It is most probable that genetic selection has taken place for increased salt tolerance in the evolu-
tion of at least some taxa found growing in both saline and nonsaline environments [111]. It was also
found from the present data that seed germination is controlled by both osmotic and ionic factors [92,112].
BIOLOGY AND PHYSIOLOGY OF SALINE PLANTS 571
TABLE 4 Effect of Time on Seed Germinability in Two Haloxylonspp.
Initiation of germination Germination
Species Time (min.) (%)
H. salicornicum 09 AM 60 26.6
(wt. 62.6 mg/100 seeds) 10 AM 105 20.0
11 AM 90 13.3
12 Noon 180 26.6
01 PM 75 13.3
02 PM 60 26.6
03 PM 45 33.3
H. recurvum 09 AM 120 06.6
(wt. 93 mg/100 seeds) 10 AM —a —
11 AM ——
12 Noon — —
01 PM 75 20.0
02 PM ——
03 PM ——
aNil.
Source:Ref. 29.