E. Medina et M. Francisco, OSMOLALITY AND DELTA-C-13 OF LEAF TISSUES OF MANGROVE SPECIES FROM ENVIRONMENTS OF CONTRASTING RAINFALL AND SALINITY, Estuarine, coastal and shelf science, 45(3), 1997, pp. 337-344
Neotropical species of the genera Rhizophora, Laguncularia and Avicenn
ia grow in environments of variable salinity and flooding stress. Spec
ies of Rhizophora predominate in riverine and low-energy coastal fring
e environments with continuous water movement, while Laguncularia race
mosa, and particularly Avicennia germinans, grow in areas with stagnat
ing water. Avicennia germinans appears to have the largest range of sa
linity tolerance. The osmotic characteristics of Rhizophora spp., L. r
acemosa and A. germinans in riverine and coastal environments of north
-eastern Venezuela are described and correlated with edaphic and clima
tic factors. Mature, fully-exposed leaves were collected in humid rive
rine sites (San Juan River Estuary, Monagas and Sucre States), and sea
sonally dry coastal fringe habitats (the Unare Coastal Lagoon, and the
Chimana Islands off-shore Puerto de La Cruz, Anzoategui State). Clean
ed leaf samples were frozen until measurement of leaf dimensions, chlo
rophyll, phosphorus and nitrogen contents, delta(13)C, osmolality of c
ell sap, and cell sap content of Na, K and Cl. Results indicate: (1) i
n all species, leaf sap osmolality is highly and positively correlated
with interstitial water salinity, and negatively correlated with leaf
area; (2) nitrogen and phosphorus contents of leaves are generally lo
wer in dry areas, but average values are not significantly different.
Therefore, it appears that nutrient deficiency is not a main factor de
termining variations in community structure. Nitrogen content per unit
dry weight is, in general, twice as high in A. germinans compared to
Rhizophora species and L. racemosa; (3) cell sap osmolality is mostly
explained by the concentration of Na and Cl; (4) osmolality of riverin
e plants (957-1253 mmol kg(-1)) is lower than that of coastal plants (
1558-1761 mmol kg(-1)); and (5) delta(13)C values are more negative in
riverine (-27.4 to -28.1 parts per thousand) than in coastal plants (
-25.4 to -27.2 parts per thousand), indicating a higher water-use effi
ciency in the latter. Coastal plants have a higher water-use efficienc
y but their growth is inhibited by salinity stress. (C) 1997 Academic
Press Limited.