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Marine Ecology Progress Series

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MEPS 493:141-154 (2013)  -  DOI:

Elevated ammonium concentrations and low light form a dangerous synergy for eelgrass Zostera marina

Beatriz Villazán1, Morten F. Pedersen2,*, Fernando G. Brun1, Juan J. Vergara1

1Departamento de Biología, Area de Ecología, Facultad de Ciencias del mar y Ambientales, Universidad de Cádiz, 11510 Puerto Real, Cádiz, Spain
2Department of Environmental, Social and Spatial Change (ENSPAC), Roskilde University, PO Box 260, 4000 Roskilde, Denmark
*Corresponding author. Email:

ABSTRACT: We studied the effect of ecologically relevant ammonium concentrations and light on several morphological and physiological properties, nitrogen metabolism and carbon reserves of eelgrass Zostera marina L. Eelgrass was grown under mesocosm conditions at 3 levels of ammonium enrichment (target concentrations of 0, 10 and 25 µM) and 2 levels of light (low and high light). High ammonium supply combined with low light had a negative effect on several morphological and physiological response parameters, while no such effects were found when ammonium was supplied under high light. N enrichment caused an increase in the content of total N, intracellular ammonium, free amino acids and residual N in the plants and this response was more pronounced under low-light conditions than under high light. The soluble proteins content decreased, in contrast with external ammonium enrichment. The accumulation of free amino acids and residual N in NH4+-enriched plants was followed by a substantial drop in carbohydrate reserves (sucrose and starch), which was larger in plants grown under low-light conditions. Our results indicate that N enrichment increases the demand for C skeletons and energy, and that photosynthesis cannot supply enough C and energy to cover that demand under low-light conditions. Eelgrass plants exposed to reduced light conditions, for example close to their depth limit or when covered by drift macroalgae, may thus be especially susceptible to enhanced ammonium concentrations. Our study demonstrates that ammonium toxicity may explain why eelgrass and other seagrasses deteriorate under nutrient-rich, low-light conditions.

KEY WORDS: Dissolved inorganic nitrogen · Light · Nitrogen metabolism · Carbon reserves · Seagrass · Eutrophication

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Cite this article as: Villazán B, Pedersen MF, Brun FG, Vergara JJ (2013) Elevated ammonium concentrations and low light form a dangerous synergy for eelgrass Zostera marina. Mar Ecol Prog Ser 493:141-154.

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