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Marine Ecology Progress Series

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MEPS 295:49-55 (2005)  -  doi:10.3354/meps295049

Nutrient dynamics of seagrass ecosystems: 15N evidence for the importance of particulate organic matter and root systems

Victor Evrard1,*, Wawan Kiswara1,2, Tjeerd J. Bouma1, Jack J. Middelburg1

1Centre for Estuarine and Marine Ecology, Netherlands Institute of Ecology (NIOO-KNAW), PO Box 140, 4400 AC Yerseke,The Netherlands
2Indonesian Institute of Sciences (LIPI), Jl. Pasir Putih No. 1 Ancol Timur, Jakarta Utara 14430, Indonesia

ABSTRACT: The availability of nitrogen in sediment phytodetritus to seagrass was investigated in 5 tropical species (Thalassia hemprichii, Halodule uninervis, H. pinifolia, Halophila ovalis/ovata and Syringodium isoetifolium) from Indonesia. 15N-labeled phytodetritus was injected into the sediment and the appearance of 15N in the roots, the rhizomes and the leaves of the plants were measured after 1, 2, 4 and 8 d. The transfer of 15N from sediment phytodetritus to the plant tissues was very rapid (within 1 d) and continued over the 8 d period, indicating an efficient retention of the phytodetritus and a net mineralization of nitrogen rather than an immobilisation by bacteria. Relative enrichment of roots versus leaves indicated that 15N was taken up by the roots and then transferred to the leaves. The combined efficiency of seagrass canopy-induced trapping and retention of sestonic particles and root-uptake, results in the acquisition of nutrients released upon mineralization of particulate organic matter (POM), giving them a competitive advantage over other primary producers in oligotrophic environments.

KEY WORDS: Tropical seagrass · Nutrient uptake · Canopy · 15N · Mineralization · Phytodetritus

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