SOIL-PLANT INTERACTIONS IN A NEOTROPICAL MANGROVE FOREST - IRON, PHOSPHORUS AND SULFUR DYNAMICS

We examined soil porewater concentrations of sulfate, alkalinity, phos phorus, nitrogen, and dissolved organic carbon and solid phase concent rations of pyrite in relation to mangrove species distributions along a 3.1-km-long transect that traversed a 47.1-km(2) mangrove forest in the Dominican Republic. Iron, phosphorus, and sulfur dynamics are clos ely coupled to the activity of sulfate-reducing bacteria, the primary decomposers in anoxic soils of mangrove ecosystems. Patterns in the ch emistry data suggested that sulfate reduction rates and storage of red uced sulfur were greater in the inland basin forest dominated by Lagun cularia racemosa than the Rhizophora mangle dominated forest of the lo wer tidal region. The distribution of Laguncularia was significantly c orrelated with concentrations of total phosphorus (r = 0.99) and disso lved organic carbon (r = 0.86), alkalinity (r = 0.60), and the extent of sulfate depletion (r = 0.77) in the soil porewater and soil pyrite concentrations (r = 0.72) across the tidal gradient. Leaf tissue chemi stry of Laguncularia in was characterized by lower C:N and C:P ratios that could fuel the higher rates of decomposition in the Laguncularia- dominated forest. We suggest that a plant-soil-microbial feedback cont ributes to the spatial patterning of vegetation and soil variables acr oss the intertidal zone of many mangrove forest communities.