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International Journal of Horticulture 2014, Vol.4, No.7, 32
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37
spray and to minimize water loss through transpiration.
Lower visual ratings in plants sprayed with seawater
were the results of the presence of chlorotic and necrotic
leaves, which conforms to the earlier studies on
Miscanthus sinensis
and
Pennisetum alopecuroides
(Scheiber et al., 2008).
3 Conclusion
This study gives an insight into the ecophysiological
adaptations underlying the growth responses of
Alternanthera maritima
to air-borne salinity.
Alternanthera
maritima
is a salt spray tolerant plant with some
adaptations for survival in the strandline: (1). Reduction
of water loss through decreased leaf size, absence of
stomata on the adaxial surface and reduction of stomata
density/stomata number per leaf in the abaxial leaf
surface. (2). Adjustment to osmotic stress, by salt
accumulation, probable production of quaternary amino
compounds in the shoot and reduction of water potential.
(3). Adaptation to ion toxicity through increased leaf
and stem succulence for ion dilution. (4). Increase in K
+
content, which acts osmotically to prevent Na
+
influx
into roots and shoots. Also, since l
andscape value is
largely determined by the physical appearance of
individual plants,
Alternanthera maritima
has high
aesthetic value under salt spray, I recommend it to be
planted as a landscaping plant on sites where salt spray
is known to pose a problem.
4 Materials and Methods
4.1 Preparation of experimental plants
Uniform plants were raised in 20×26 cm perforated
plastic pots filled with 2:1 mixture (v/v) of river sand to
topsoil (Cheplick and Demetri, 1999; Khan et al., 2000)
from the vegetative stem cuttings of
Alternanthera maritima
collected from Lekki Beach in Lagos, Southern Nigeria.
4.2 Experimental location and plant treatment
This experiment was carried out in the greenhouse of
Plant Science and Biotechnology Department, Adekunle
Ajasin University, Akungba Akoko, Ondo State, Nigeria
(Lat. 7
0
N 28
1
, Long. 5
44
1
E). Filtered seawater was
collected from Lekki Beach in Southern Nigeria on a
single day in late July 2013 following the method
described by Cheplick and Demetri (1999) and used by
Griffiths and Orians (2003), De Vos et al.
(
2010) and
Conolly et al.
(
2010).
The seawater had salinity of 31
ppt and
pH of 8.21
with sodium and chloride accounting
for approximately 86% of the ions present. The seawater
was stored in a 5
-
L plastic jug and kept in a refrigerator
at 4°C and used for
the duration of the experiment.
Meanwhile, before treatment commenced, 5 plants were
randomly selected and used for the determination of
initial growth parameters. Saltwater sprays were
initiated on July 30 and lasted for 12 weeks. Plants were
sprayed with seawater at: two sprays/week (2SS) -one
spray on each of the two days), four sprays/week (4SS)
-2 sprays on each of the two days, or six sprays/week
(6SS) -three sprays on each of the two days, while
plants sprayed with deionized water three times on each
of the two days served as control. The control plants
were sprayed to account for any physical effect that the
spraying might have on plants.
Before each salt spray
treatment, plastic discs were placed over the soil surface
and around the base of each plant to prevent salt
deposition on the soil.
Plants were sprayed at an interval
of 4 hours beginning from 08:00 am in case of two and
three sprays. At each spray, plants were taken outside
and individual plant was sprayed with seawater to run
off with a portable plant mist bottle held
about
20 cm
from the side of each shoot. Salt deposited onto shoot
was estimated following the method described by
Cheplick and Demetri (1999) by using five plants not
used in the experiment but grown with the experimental
plants. Salt deposition onto shoot for 1 spray, 2 sprays
and 3 sprays equaled on average 4, 8 and 12 mg NaCl
dm
-2
leaf area day
-1
, which fall within the levels found
in the natural habitat of strandline plants (Rozema et al.,
1982; Cheplick and Demetri, 1999; Griffiths, 2006).
Plants in all treatments were randomly located onto a
single
greenhouse bench and randomly repositioned
after each saltwater
treatment (twice weekly).
Also,
p
lants were watered from the top of the soil surface at
the base of the plants once per week to flush out any
salts that might have been deposited onto the soil during
misting (Rozema et al., 1982, Cheplick and Demetri,
1999, Griffiths, 2006), so that the relative level of
airborne salt deposited onto the shoots would be the
primary cause of any observed effect rather than soil
salinity or combined effect of both. This basal method
of watering did not remove the salts deposited onto the
shoots during the application of salt sprays. Salt was
allowed to accumulate throughout the experiment,