Science Serving Maryland's Coasts
Michael Kemp, Ph.D.
Horn Point Laboratory
The Biogeochemistry of Plant-Sediment Interactions in Contrasting Ruppia maritima Beds
Nutrient cycling, with a focus on the nitrogen cycle, was observed in two beds of the seagrass Ruppia maritima. These two plant communities differed markedly in their contrasting ratios of biomass in vegetative versus reproductive shoots. Net fluxes of N2, O2, and NH4+ across the plant-sediment interface were calculated for light and dark periods. Respiration rates per unit plant biomass were virtually identical for both sites, suggesting that reproductive and vegetative shoots have the same respiratory demands. In contrast, reproductive shoots had lower rates of oxygen production per unit biomass. The site with a higher proportion of vegetative shoots had high rates of denitrification (N2 production), likely due to the higher rates of sediment nitrification stimulated by O2 release from plant roots. On the other hand, the site with plant biomass dominated by tall reproductive shoots had higher rates of NH4+ recycling, indicating that the presence of reproductive shoots enhances the nutrient quality of surrounding sediment. These findings suggest that success of seagrass transplantations would be enhanced in R. maritima beds with a balance of vegetative and reproductive shoots.
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