Effects of Nutrient Enrichment on Leaf Anatomy of Dwarf Rhizophora mangle L. (Red Mangrove)

I fertilized dwarf Rhizophora mangle trees for two yr to determine how the morphology and internal anatomy of leaves are affected by increased nutrient availability. The sclerophyllous structure of R. mangle leaves decreased on Pand NPK-fertilized trees, but not on N-fertilized and control trees. Leaves from trees treated with phosphoruscontaining fertilizers were 40 percent to 80 percent as thick as leaves on control trees. Differences in the hypodermis accounted for most differences in leaf thicknesses. In P- and NPK-fertilized trees, the thickness of the hypodermis in basal leaves was 225 (?13) Am and 207 (?11) Am, respectively, compared to 572 (?13) Am in N-fertilized and 594 (?13) Am in Control trees. Area per leaf and leaf length:width ratio did not change in response to increased nutrient availability. Nutrient deficiency rather than salinity and physiological drought appears to be the proximate cause of well-developed xeromorphic traits in leaves of dwarf red mangrove. This study provides experimental evidence of the oligotrophic-xeromorphic hypothesis that states that sclerophylly is an adaptation to P-deficient soils rather than to drought or physiological drought.