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International Journal of Horticulture 2014, Vol.4, No.7, 32
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39
http://ijh.biopublisher.ca
33
adjust osmotically through reduced xylem water
potential (Griffiths and Orians, 2003; Griffiths, 2006).
Thus, plant species growing in the strandline have
adapted to salt spray in various ways (Rozema et al.,
1985; De Vos et al., 2010).
Alternanthera maritima
(Mart.) A.St.-Hil. (Beach
Alternanthera
) belongs to the family Amaranthaceae.
It is an herbaceous, dicotyledonous and perennial
plant with fleshy creeping stem, procumbent or
prostrate and glaborous, rooting at nodes. Its leaves
are narrow to base, sessile, blade oblong, oblanceolate,
obovate or oval, succulent, apex obtuse to acute,
mucronate and glabrous. Its Inflorescences are axillary,
sessile, heads white to stramineous, globose to ovoid.
Flower clusters axillary up to about 1.5 cm long,
inconspicuous and silvery white on erect shoot. Seeds
are subglobose and about 1.5 mm in size (Hutchinson
et al., 1968). It is widely distributed in the coast of
Africa where it often forms part of the major
contributors to the biomass in the strandline. Since it
grows naturally in the strandline, I hypothesized that it
has some adaptations for survival in the area. A
greenhouse experiment was therefore undertaken to
determine the effect of different levels of salt spray on
the growth of
Alternanthera maritima
and to have an
insight into the ecophysiological adaptations
underlying the responses.
Furthermore, landscaping and gardening projects in
coastal regions have called for selection of plants that
are tolerant to seawater sprays considering the high
level of the death of sea side horticultural plants
(Scheiber et al., 2008;
Conolly et al., 2010
). For
landscape plantings to be successful, they must not
only survive, but meet high aesthetic standards
(Marcum et al., 2005). Many coastal plants have
shown necrotic damage due to salt sprays as found in
Solidago puberula
,
Solidago rugosa
,
Gaylussacia
baccata
and
Quercus ilicifolia
(Griffiths and Orians,
2003),
Pinus
rigida
(Griffiths and Orians, 2004),
Deschampsia
caespitosa
and
Melica
californica
(Hunter and Wu, 2005),
Miscanthus sinensis
and
Pennisetum Alopecuroides
(Scheiber
et al
.,
2008) and
Diodia maritima
(Kekere and Bamidele, 2012).
However, there have been reports of plants that
showed high resistance to necrotic damage (Griffiths
and Orians, 2003; Kekere, 2013; Kekere, 2014).
Landscape value is largely determined by the physical
appearance of individual plants, and plants with high
necrotic damage are not attractive in gardens and
landscapes (Bernstein et al., 1972). In view of this,
leaf necrosis, an aesthetically important symptom of
damage was also assessed on the leaves of
Alternanthera maritima
in response to salt spray, in
order to ascertain its suitability for landscape projects
in coastal beaches.
1 Results
The physicochemical properties of the soil include:
5.48 pH, 20.42 ppm N, 3.56 ppm P, 3.56 (meg/100g)
K, 2.32 (meg/100g) Ca, 2.60 (meg/100g) Mg, 8.2
(meg/100g) CEC, 3.67% C, 80.68% sand, 12.06% silt
and 8.36% clay, which was characterized as a sandy
soil. Survivorship was 100% for both plants sprayed
with seawater and deionized water (Table 1).
Saltwater sprays significantly decreased leaf area with
increasing level of applications. Plants that were
exposed to salt spray showed
a greater stem girth,
number of leaves, number of branches and plant
height. Only stem girth and number of leaves were
however significant when compared to the control
(Table 1). Seawater treatments had effect on shoot but
not root growth (Table 1). In fresh and dry mass
variables (Table 2), stem and shoot mass were
significantly higher under seawater treatment than in
the control. Although, salt spray increased leaf mass, it
was not significantly different from those sprayed
with deionized water. In addition, total biomass and
relative growth rate increased while root: shoot ratio
and leaf total chlorophyll (LTC) decreased as a result
of seawater application (Table 2).
Except the root, air-borne salt application increased
succulence in plant parts (Table 3). Leaf and stem
moisture content increased over the control by
approximately 19.80% and 5.69% respectively at the
highest level of salt spray (6SS). Plant xylem water
potential was lower under air-borne salinity
treatment than did control plants, and they were
significantly different from each other as the
application level increased (Table 3). Mid-day xylem
water potential values were lower than those of the
predawn. Except for Ca
2+
and Fe
2+
in the stem, salt
spray decreased the concentration of the essential
elements in the shoot. N content increased in the aerial
parts of salt-sprayed plants, but significantly differ
from the control only in the leaf. Na
+
and Cl
-
ions
accumulated in the aerial parts of salt-treated plants
with increasing level of salt applications, resulting in