Nutrient relations of dwarf <Emphasis Type="Italic">Rhizophora mangle</Emphasis> L. mangroves on peat in eastern Puerto Rico |
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Authors: | Ernesto Medina Elvira Cuevas Ariel E Lugo |
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Institution: | 1.Centro de Ecología,Instituto Venezolano de Investigaciones Científicas,Caracas,Venezuela;2.International Institute of Tropical Forestry,USDA Forest Service,San Juan,USA;3.Department of Biology,University of Puerto Rico,San Juan,USA |
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Abstract: | Dwarf mangroves on peat substrate growing in eastern Puerto Rico (Los Machos, Ceiba State Forest) were analyzed for element
concentration, leaf sap osmolality, and isotopic signatures of C and N in leaves and substrate. Mangrove communities behind
the fringe presented poor structural development with maximum height below 1.5 m, lacked a main stem, and produced horizontal
stems from which rhizophores developed. This growth form departs from other dwarf mangrove sites in Belize, Panama, and Florida.
The dwarf mangroves were not stressed by salinity but by the low P availability reflected in low P concentrations in adult
and senescent leaves. Low P availability was associated with reduced remobilization of N and accumulation of K in senescent
leaves, contrasting with the behavior of this cation in terrestrial plants. Remobilization of N and P before leaf abscission
on a weight basis indicated complete resorption of these nutrients. On an area basis, resorption was complete for P but not
for N. Sulfur accumulated markedly with leaf age, reaching values up to 400%, compared with relatively modest accumulation
of Na (40%) in the same leaves. This suggests a more effective rejection of Na than sulfate at the root level. Dwarf mangrove
leaves had more positive δ13C values, which were not related to salinity, but possibly to drought during the dry season due to reduced flooding, and/or
reduced hydraulic conductance under P limitation. Negative leaf δ15N values were associated with low leaf P concentrations. Comparison with other R. mangle communities showed that P concentration in adult leaves below 13 mmol kg−1 is associated with negative δ15N values, whereas leaves with P concentrations above 30 mmol kg−1 in non-polluted environments had positive δ15N values. |
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