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INFLUENCE OF THE SEAGRASS THALASSIA TESTUDINUM ON THE COMMUNITY COMPOSITION AND ACTIVITY OF SULFATE-REDUCING BACTERIA IN AN ESSENTIAL COAST MARINE HABITAT
Citation:
Devereux, R D., A. C. Smith, J. E. Kostka, AND D F. Yates. INFLUENCE OF THE SEAGRASS THALASSIA TESTUDINUM ON THE COMMUNITY COMPOSITION AND ACTIVITY OF SULFATE-REDUCING BACTERIA IN AN ESSENTIAL COAST MARINE HABITAT. Presented at ASLO/AGU Ocean Sciences Meeting, Honolulu, HI, Feb 18-22, 2002.
Description:
Biogeochemical cycling of nutrients and sulfate reduction rates (SRR) were studied in relation to the community composition of sulfate-reducing bacteria SRB) in a Thalassia testudinum bed and in adjacent unvegetated areas. Sampling took place in Santa Rosa Sound, Pensacola, Florida, during February and July 2001. There was a noticeable downward extension of the Thalassia root zone by approximately 4 cm in summer compared to winter that had a profound effect on SRR, sediment geochemistry, and bacterial cell numbers. Depth-integrated SRR were three times higher in vegetated (1-7 mmol m-2 d-1) versus unvegetated (0-1 mmol-2 d-1) sediments during winter. Rates measured during summer were seven times higher in vegetated
(5-10 mmol-2 d-1) versus invegetated (0-3 mmol-2 d-1) sediments. SRR were consistently higher in surface sediments (0-3 cm depth) at the vegetated site. Overall, sulfate concentrations were high, and sulfate depletion was only observed at the unvegetated site during summer. Little accumulation of sulfides, a mid-depth maximum of NH4+ with low NO3- concentrations were observed throughout all vegetated cores. Organic carbon (OC) content did not change from winter to summer, but OC in vegetated sediments was consistently
twice that of OC in unvegetated sediments. During summer, most probable number (MPN) counts of SRB were two orders of magnitude higher in vegetated (7.0 x 106 cells ml-1 sediment), as compared to unvegetated sediment (2.0 x 104 cells ml-1 sediment). Direct counts using epiflorescence microscopy determined that total bacterial cell numbers were higher than SRB from MPN counts. Molecular characterization of the SRB communities via restriction fragment length polymorphism (RFLP) analysis of the dissimilatory sulfite reductase gene (dsr) indicated that both vegetated and unvegetated sites were extremely diverse with respect to SRB species. The sequencing of unique clones has identified the Desulfobacteriaceae family as being important for sulfate reduction activity in the vegetated sediment. These data indicate that depth of the root zone and the physiologically active growth state of above-ground biomass affect the activities and cell numbers of SRB by controlling organic matter and oxidants delivered to the sediment. An intense sulfate-reduction zone appears to be fueled by vegetation just above the depth of the root zone.