Basic HTML Version
International Journal of Horticulture 2014, Vol.4, No.13, 64
-
71
http://ijh.biopublisher.ca
68
to the results obtained in this study,
Scaevola sericea
seedlings had reduced stem mass, leaf mass, shoot
mass and total biomass with increasing level
of sea
spray (Goldstein et al., 1996). Reduction in growth
parameters led to biomass reduction. Leaf and stem
succulence increase by salt spray in
P. vaginatum
agrees with the study on
Crambe maritima
(De Vos et
al., 2010), which is an adaptation for ion dilution
(Rozema et al., 1985). Salt-tolerant plants reduce their
xylem water potential as an adaptation against osmotic
stress (Touchette, 2009). In an earlier study, there was
a significant reduction in xylem water potential in
Solidago puberula
,
Solidago rugosa
,
Gaylussacia
baccata
,
Myrica pensylvanica
,
Pinus rigida
and
Quercus ilicifolia
by salt sprays, indicating that salt
spray caused water stress and might be inhibiting
physiological processes in the plant (Griffiths and
Orians, 2003). Na
+
and Cl
-
ions accumulation as well
as reduction in certain nutrients in the shoot indicated
that high concentrations of seawater can influence ion
distribution, so that they can contribute to the osmotic
potential, and thereby increase the protection against
osmotic stress (Touchette, 2009). Nitrogen increase in
shoot was probably as a result of its use in the
synthesis of specific N compounds such as amino
acids (proline and aspartic acids), amides (glutamine
and asparagine) and the stress-related proteins, which
help in reduction of osmotic stress (Ashraf and Harris,
2004). Na
+
accumulation on shoot is usually
associated to salt spray, which interferes with the
function of potassium as a cofactor in various
reactions (Al-Karaki, 2000). They further stated that
the K
+
deficiency of salinized plants was inversely
correlated to the increased accumulation of Na
+
,
indicating the existence of competition effects
between Na
+
and K
+
ions which most likely share the
same transport system at the root surface. Not only
Na
+
and K
+
contents, but also the Na: K ratio can be
used as phyto-physiological parameters for screening
less sensitive plants for NaCl stress (Al-Karaki, 2000).
A high Na: K ratio indicates metabolic disorders such
as a reduction in protein synthesis and enzyme
activities and an increase in membrane permeability
(Al–Karaki, 2000).
Lower visual ratings in plants sprayed with seawater
are usually caused by salt damage on leaf. Salt spray
led to chlorosis and necrotic damage of the leaves of
Miscanthus sinensis
and
Pennisetum alopecuroides
(Scheiber et al., 2008) thereby reducing its aesthetic
value. However, high visual ratings recorded in
Kyllinga peruviana
(Kekere, 2014b)
and
Alternanthera
maritima
(Kekere, 2014c) under salt spray informed
their recommendation for beach landscaping.
3 Conclusion
This study revealed that salt spray is an important
factor that affects the growth of seashore paspalum
(Paspalum vaginatum)
in the coastline. Although, its
growth was reduced by salt spray, it is a salt spray
tolerant plant and has developed some adaptations for
growth along the seashore. It folded its leaves and
decreased the leaf size to reduce the surface area
available for salt deposition and minimize water loss
through transpiration. The shiny waxy leaf surface
made it to reduce entry of salt. It adjusted osmotically
to salt stress by accumulating Na
+
and Cl
-
ions, and
likely produced quaternary amino compounds in the
shoot, evident by increased nitrogen level. It adjusted
to water stress through reduction of xylem water
potential. It increased leaf and stem succulence, which
are adaptations for ion toxicity reduction through
dilution.
P. vaginatum
is a good landscape plant in
coastal beaches not only because it is tolerant to salt
spray, but also as a result of its high aesthetic value, as
determined by good visual ratings of the plant under
different levels of salt spray. Besides, since l
andscape
value is largely determined by the physical appearance
of individual plants, t
his research has revealed that the
growth of
P. vaginatum
and its ability to maintain high
aesthetic value under salt spray are largely responsible
for its use as a landscaping plant in coastal beaches. It
is therefore important to consider tolerance to salt
spray in the selection of plants for landscaping projects
in coastal beaches. These findings are important to the
end users, ornamental growers, landscapers and
residents of coastal communities.
4 Materials and Method
4.1 Pot preparation and experimental set up
Freshly rhizomes with 2 vegetative nodes of
P.
vaginatum
were collected at Lekki Beach in Lagos
Nigeria. They were immediately planted 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). Plastic pots were initially kept in
shady, moist conditions to stabilize and later
transferred and placed on the Greenhouse bench of
Plant Science and Biotechnology Department,
AdekunleAjasin University,AkungbaAkoko, Ondo State,