Factors influencing Rhizophora mangle L. seedling development in Everglades carbonate soils

Nutrient limitation, soil waterlogging, and soil salinity have been hypothesized as the principal factors limiting the development of neotropical mangrove forests. A mesocosm experiment was initiated to investigate these alternative factors, using low-nutrient soils from the south Florida Everglades. Nitrogen (N), phosphorus (P), aeration, and salinity treatment effects on Rhizophora mangle L. seedling leaf area, stem elongation, and biomass development were determined. Phosphorus rather than nitrogen was the important macro-nutrient limiting R. mangle leaf area, and root and leaf biomass development in the mesocosm experiment. A subsequent P enrichment experiment was conducted in the field to substantiate mesocosm findings. Under P enrichment in the field, seedling stem elongation rates increased from 0.03 mm d −1 to 0.20 mm d −1 and leaf area increased from 25 cm 2 to 75 cm 2, relative to unfertilized controls. Soil aeration stimulated root biomass development 40% in the mesocosm experiment. Sodium chloride at 32‰ resulted in branch initiation with no leaf response; however, hypersaline conditions greater than 45‰ caused denaturing of terminal buds. Thus, without hypersalinity stress, P is identified as a dominant factor limiting R. mangle foliar and stem development in low nutrient carbonate soils. Soil anoxia also influences root development and may moderate stem elongation responses to P fertilization in the field.