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International Journal of Horticulture 2014, Vol.4, No.13, 64
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71
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67
The percentage organic content however decreased
with increase in the level of salt spray in leaf and stem.
Na: K ratio values were significantly higher in leaf
and stem of plants sprayed with seawater than in those
sprayed with de-ionized water. Though, Na
+
and Cl
-
increased slightly in the root of plants under salt spray,
root nutrient content was generally not affected. As
compared to the control treatment, salt spray led to a
significant increase in the necrotic leaf area with
increasing level of application (Table 5). It also
resulted in a decline in the visual rating of the plant
but ANOVA test showed that the reduction was not
significant at all levels of sea spray in comparison to
the control.
Table 5 Some anatomical parameters measured on the leaf of
Paspalum vaginatum
after 12 weeks of exposure to salt spray
Level of salt spray Necrotic leaf area (%)
Visual ratings
CSS
5.74
a
5.00
a
2SS
15.13
b
4.68
a
4SS
15.32
b
4.49
a
6SS
16.95
b
3.85
ab
Note: Each value is a mean of 6 replicates; Means with the
same letter(s) in superscript in the same column are not
significantly different at P ≥0.05 (Tukey HSD); CSS=deionized
water sprays (control), 2SS=two salt sprays per week, 4SS=four
salt sprays per week, 6SS=six salt sprays per week. Visual
ratings scale: 1=no green foliage, 2=25% green foliage, 3=50%
green foliage, 4=75% green foliage and 5=all green foliage
2 Discussion
The ratio 2:1 river sand to top soil is a sandy soil with
low nutrient content typical of beach soil (Cheplick
and Demetri, 1999; Khan et al., 2000). Beach plants
grow naturally in very sandy soil that tends to be
nutrient deficient, and because the soil is porous,
leaching rate is high and salt does not accumulate in
the root zone (Griffiths and Orians, 2003). The
observed effect on the plant was not due to nutrient
unavailability but salt spray, because no growth defect
was observed in the control plants. Leaf folding in
P.
vaginatum
is an adaptation to reduce salt deposition
on leaf surface and mimimize water loss through
transpiration. Besides, shiny waxy leaf surface of
some seashore grasses makes them not completely
wettable, resulting in the beading of droplets on the
leaf surface and reduce entrance of harmful chlorides
(Alshammary et al., 2004; hunter and Wu, 2005).
P.
vaginatum
was tolerant to salt spray because of its
high survivorship at all levels of application. Similarly,
Gagne and Houle (2002) recorded 100% survival in
Leymus
mollis
sprayed with seawater. Salt spray
tolerant plants occupy sea-side while sensitive species
are eliminated and are found inland far away from the
beach (Scheiber et al., 2008). Growth reduction in
P.
vaginatum
sprayed with seawater agrees with what
was reported on
Leymus mollis
(Gagne and Houle,
2002) and
Myrica
.
pensylvanica
(Griffiths and Orians,
2003). Decreased stem length was affected by
reduction in internode length. In earlier studies, shoot
elongation as well as production of branches and
leaves were observed to reduce in
Miscanthus sinensis
and
Pennisetum alopecuroides
(Scheiber et al., 2008),
Crambe maritima
(De Vos et al., 2010),
Diodia
maritima
(Kekere and Bamidele, 2012),
Commelina
erecta
var.
maritima
(Kekere, 2014a) and
Kyllinga
peruviana
(Kekere, 2014b). Interestingly, reduced
plant size was assumed to be mechanism through
which the characteristic dwarf stature of strand
vegetation is maintained (Lee and Ignaciuk, 1985).
This means that the reduction in the size of the test
plant might be an adaptation to maintain the plant in
an environment where salt spray is prevalent. Leaf
number was also reported to reduce in
Pinus rigida
(Griffiths and Orians, 2004),
Crambe maritima
(De
Vos et al., 2010),
Diodia maritima
(Kekere and
Bamidele, 2012) and
Commelina erecta
subsp
maritima
(Kekere, 2014a) following exposure to salt
sprays. Reduced leaf size was due to inhibition of leaf
expansion and hence reduction of light interception
(De Vos et al., 2010). However, reduction in
P.
vaginatum
leaf size might be an adaptive fissure to
cope with salt spray related damage. Reduced leaf size
decreases the surface area available for salt deposition
and loss of water through transpiration (Morant-Manceau
et al., 2004). Reduction in total leaf chlorophyll was
largely due to damage induced by salt. It might be
caused by Na
+
and Cl
-
ions toxicity leading to necrosis
on the leaf surface. Necrotic spots on leaf resulted in a
decrease in total photosynthesis and carbohydrate
stored in the plant (Touchette, 2009). Application of
NaCl to plant foliage induced fragmented cuticles,
disrupted stomata, collapsed cell walls, coarsely
granulated cytoplasm, disintegrated chloroplasts and
nuclei, and disorganized phloem (Touchette, 2009).
Besides, certain elements are important for normal
growth and are part of chlorophyll ultrastructure.
When such nutrients are limited, chlorophyll
formation will be inhibited (Touchette, 2009). Similar