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Marine Ecology Progress Series

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MEPS 183:95-103 (1999)  -  doi:10.3354/meps183095

Nitrogen acquisition, storage, and use by the co-occurring Mediterranean seagrasses Cymodocea nodosa and Zostera noltii

George P. Kraemer*, Lucia Mazzella

Laboratorio di Ecologia del Benthos, Stazione Zoologica di Napoli, Punta San Pietro, I-80077 Ischia (NA), Italy
*Present address: Division of Natural Sciences, SUNY/Purchase College, 735 Anderson Hill Road, Purchase, New York 10577, USA. E-mail:

ABSTRACT: Shoot density, shoot, root, and rhizome tissue biomass and N content, and N assimilation by leaf and root tissues of the 2 co-occurring seagrasses Cymodocea nodosa and Zostera noltii were measured over the course of a year at a central Mediterranean site. Concentrations of dissolved inorganic nitrogen (DIN; NH4+, [NO3- + NO2-]) co-varied in the canopy water. Sediment NH4+ concentration varied within the top 10 cm of the sediments, while those of [NO3- + NO2-] were virtually invariant. C. nodosa and Z. noltii appeared to contribute to the replenishment of the sediment DIN reservoir as growth declined and senescence ensued in the fall; the peak in plant-based N preceded the peak of sediment DIN by 1 to 2 mo. C. nodosa had a June peak in glutamine synthetase (GS) activity in leaf tissue, and showed greater variation over the course of the study than did Z. noltii, for which there was a February peak in shoot GS activity. The leaves, rhizomes, and roots within each species exhibited different patterns of tissue N content over the course of the year, indicating different strategies of N storage and subsequent use. Within a species, assimilated N was first allocated to leaves, then rhizomes and roots. Leaves, in addition to rhizomes, appear to have a N storage function. C. nodosa maintained high tissue N levels for longer periods than did Z. noltii, suggesting that clonal modules of C. nodosa were more physiologically integrated than modules of Z. noltii. The average potential for N assimilation through Z. noltii tissues was estimated to be roughly 43% of the total for C. nodosa and Z. noltii.

KEY WORDS: Cymodocea · Zostera · Seagrass · Nitrogen · Glutamine synthetase

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