MEPS 225:197-204 (2002)  -  doi:10.3354/meps225197

Effects of sea level rise on growth of Spartina anglica and oxygen dynamics in rhizosphere and salt marsh sediments

Marianne Holmer*, Britta Gribsholt, Erik Kristensen

Institute of Biology, SDU-Odense University, Campusvej 55, 5230 Odense M, Denmark

ABSTRACT: The effect of sea level rise on the growth of Spartina anglica seedlings and on key sediment biogeochemical variables (oxygen concentrations and sulfur cycling) was studied for 4 mo in a laboratory experiment. S. anglica, grown under drained and waterlogged conditions, showed no significant differences in leaf elongation and above-ground biomass between treatments. Sulfate reduction rates were not significantly different between treatments (4.1 and 5.3 mmol m-2 d-1, respectively), and although pools of reduced sulfides were high (12.1 to 14.9 mol S m-2), no dissolved sulfides were detected in the sediments. Measurements of oxygen concentrations in rhizosphere sediment done with microelectrodes revealed a distinct oxic microzone of up to 2.5 mm around the roots of S. anglica. The oxic microzone comprised 30 to 60% of the S. anglica rhizosphere sediment, suggesting that the root-mediated oxygen supply to the rhizosphere has profound effects on the microbial processes in the sediments. The sulfate reduction was probably hampered due to the root-mediated loss of oxygen from the plants. There was no difference in oxygen dynamics in the rhizosphere between treatments, indicating that S. anglica is efficient in oxidizing the sediments also under waterlogged conditions. The root-mediated loss of oxygen from S. anglica counteracts the expected changes in sediment conditions as a consequence of sea level rise, e.g. accumulation of phytotoxic compounds such as sulfides. The results suggest that possible negative impacts of sea level rise are more likely to be found for plants with less developed root systems.

KEY WORDS: Spartina anglica · Salt marsh sediment · Sulfur cycling · Oxygen dynamics · Plant-sediment interactions

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