Page 10 - International Journal of Horticulture

International Journal of Horticulture 2014, Vol.4, No.13, 64-71
http://ijh.biopublisher.ca
69
Nigeria (Lat. 70 N 281, Long. 50 44 1 E). The soil had
5.48 pH, 20.42 ppm N, 3.56 ppm P, 3.56 (meg/100 g)
K, 2.32 (meg/100 g) Ca, 2.60 (meg/100 g) Mg,
8.2 (meg/100g) CEC, 3.67% C, 80.68% sand, 12.06%
silt and 8.36% clay (Kekere, 2014a, 2014b). It is
typical of a beach soil which is sandy and low in
nutrient content, and because the soil is porous,
leaching rate is high and salt does not accumulate in
the root zone (Griffiths and Orians, 2003).
Air-borne seawater collected off the shore at Lekki
Beach in Lagos Nigeria on a single day in late
September 2013 was used. The seawater was collected
by the conventional method of arranging salt spray
collectors parallel to the coastline at about 10 m from
mean seawater level (mean tide line). The salt spray
collector was made up of polypropylene filter gauze
wrapped over a 30 cm long plastic tube placed
vertically in a beaker. The collectors were fixed on the
ground with about 20 cm of the upper part exposed.
The beaker was to collect precipitation and prevent
loss of trapped water (Griffiths and Orians, 2003; De
Vos et al., 2010; Conolly et al., 2010). The seawater
was stored in plastic jug and kept in a refrigerator at
4°C and used for the duration of the experiment. It had
salinity of 31 ppt, with sodium and chloride
accounting for approximately 86% of the ions present.
Spray treatments began on 30 September 2013 and
lasted for 12 weeks. Plants were sprayed twice/week
(on Mondays and Thursdays) with seawater at: 2
sprays/week (2SS)-1 spray on each of the two days), 4
sprays/week (4SS)-2 sprays on each of the two days or
6 sprays/week (6SS)-3 sprays on each of the two days.
In the control treatment, plants were sprayed with
de-ionized water 3 times on each of the two days to
account for any mechanical or physical effects of the
misting process. Plants were sprayed at 4 hour interval
starting 08:00 am by removing plants from the
Greenhouse, taking them outside, and spraying
individual plant to run-off with all the aerial parts
equally exposed. A plant mist bottle held about 20 cm
from the shoot was used for spraying. The salt loads at
each level of spray were estimated following the
commonly used method described by (Cheplick and
Demetri, 1999). Five plants not used in the experiment
but grown with the experimental plants were each
immersed in 150 ml of de-ionized water and the
conductivity determined. The same shoot was sprayed
once with seawater, immersed into 150 ml of
de-ionized water, and the conductivity increase was
recorded. The conductivity increase was also recorded
after the same shoot was sprayed twice and three
times respectively following immersion in 150 ml of
de-ionized water. This was repeated for all the 5 plants.
Salt deposition was estimated per leaf area surface for
each of the three seawater treatments at each
application. The accumulated salt onto shoot for 1
spray, 2 sprays and 3 sprays equaled on average 4 mg,
8 mg and 12 mg NaCl dm-2 leaf area day-1, which fall
within the levels found in the natural habitat of beach
plants (Barbour et al., 1985; Griffiths, 2006). 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. Also, plants 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, which did not remove the salts deposited onto
the shoots. This was to ensure 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 soil salinity and
sea spray (Rozema et al., 1982; Cheplick & Demetri,
1999; Griffiths, 2006). Salt spray was allowed to
accumulate throughout the experiment, which is
realistic in the field because in years with infrequent
rain, salt spray is not washed off during the summer
growing season (Cheplick and Demetri, 1999;
Cheplick and White, 2002).
4.2 Survival and growth measurement
At the end of the study, plant survival was recorded
while plant height, leaf area and stem girth were
measured with meter rule, leaf area meter (LI-COR
300 model) and digital vernier caliper (model 0~200
mm) respectively. The number of leaves and branches
were counted. Number of roots was counted while
their length measured after harvest. Fresh and dry
mass of plant parts were weighed, while root: shoot
ratio and relative growth rate (RGR) were calculated
using the commonly used formulae: root mass/shoot
mass and (ln mass2-ln mass1)/ time respectively.
4.3 Determination of water status
Moisture content and xylem water potential were the
two aspects of water status determined. Moisture
content was calculated with the commonly used
formula: [(fresh mass– dry mass)/dry mass] x 100
while plant xylem water potential was measured with
a plant moisture-stress instrument (PMS Instrument