Basic HTML Version
International Journal of Marine Science 2013, Vol.3, No.9, 72-78
http://ijms.sophiapublisher.com
77
accumulation of carbon in the branches more than
even in the main stem. Even though similar pattern of
TOC was found to occur in leaves of two species with
age/dbh, magnitude of contribution by
L. racemosa
with its low volume of fleshy leaves is much lower
than that of
B. gymnorrhiza
which possesses larger
and thick leaves. TOC partitioning among the plant
components are highly species specific and also
appears to depend on habitat conditions such as aridity
and soil salinity (Clough et al
.
, 1997).
Gradual decline of A/B (biomass) of
B. gymnorrhiza
with dbh (Figure 2) is analogous to observations
recorded by Matusui (1998) with B/A (biomass)
changes with dbh of
Rhizophora stylosa
in Iriomote
island, Japan. Root development, especially the radial
roots and negatively geotropic roots such as the knee
roots of
B. gymnorrhiza,
that takes place with age,
may contribute to slightly higher magnitude of
below-ground biomass or carbon accumulation, when
compared to that of above carbon accumulation.
L.
racemosa
plants most often occur in less inundated
landward areas of the mangrove stands in the
Negombo estuary and do not develop many knee roots
(which are characteristically much less in diameter)
unlike
B. gymnorrhiza
that occupies more inundated
terrain of the mangrove areas and forms greater
numbers of large knee roots. Increasing below ground
biomass/carbon in
B. gymnorrhiza
relative to
L.
racemosa
may have resulted the opposing patterns of
A/B (TOC) with age (dbh) of the two species,
indicating magnitude, period and frequency of
inundation influences the biomass/carbon distribution
in mangrove plants.
Moreover, TOC/ plant in
L. racemosa
(mean dbh =
8.62 cm) is greater (25.90 ± 8.04 kg/plant) than that of
B. gymnorrhiza
(19.02±8.42 kg/plant) of which the
mean diameter is 5.5 cm. Profuse branching of
L.
racemosa
makes an important contribution in carbon
sequestration capacity of the species. Percentage
potentially sequestered carbon stock in any girth/age
class of
L. racemosa
was greater than that of
B.
gymnorrhiza,
revealing that
L. racemosa
is superior in
carbon sequestration in all age/girth classes. This
provides useful knowledge in selecting mangrove
species for replanting and maintaining mangrove
plantations for carbon assimilation purposes.
Moreover, destruction of
L. racemosa
may contribute
significantly to loss of sequestered carbon in a
mangrove ecosystem.
3.2 Development of allometric relationships between
dbh and TOC
Estimation of organic carbon content in mangrove
plants presents a pragmatic measure to determine the
carbon sequestration capacity of individual plants,
species and communities. Although allometric
relationships have been developed between dbh and
biomass for a number of mangrove species,
(Amarasinghe and Balasubramaniam, 1992b; Comley
and McGuinness, 2005; Chave et al., 2005;
Komiyama et al
.
, 2005) allometric relationships
between dbh and TOC for mangrove species is sparse.
This is the first study of this nature conducted in Sri
Lanka that probed into allometry of total organic
carbon in mangrove biomass and it assists in
estimating carbon emission from mangrove
deforestation.
4 Materials and Methods
4.1 Selection of sample trees
The dbh of
B. gymnorrhiza
plants in the study area
ranged between 2 cm and 14 cm and the height from
2.0~9.5 m. Fourteen plants that represent the above
ranges were harvested to determine biomass and TOC.
Likewise
,
10
Lumnitzera racemosa
plants that
represent the natural range of dbh from 4~16 cm and
tree height from 4.0~10.0 m were selected from
Kadolkele mangrove area in Negombo estuary, Sri
Lanka (7
°
1
1
′42.1
8
″N ~ 79
°
50′47.50″E) to measure the
biomass and TOC of plant components.
4.2 Determination of mangrove plant biomass
Each sample tree was cut at ground level using a saw
and separated manually into trunk, branches, leaf
fractions and reproductive parts. The trunk diameters
of each sample tree were measured at ground level
(D
0
), 1 m above ground level (D
1
) and 1.3 m above
ground level/dbh level (D
1.3
). Roots of each sample
tree were excavated and washed with pressurized
water (Comely and McGuinnes, 2005, Komiyama,
2005).
Total fresh weight of stems, branches, leaves,
reproductive parts and roots of each plant was
measured in the field with an electronic balance of 1.0 g
accuracy. Samples from each component were
oven-dried at 65
℃
to constant weight. Fresh to dry