Toxicity of reduced nitrogen in eelgrass (Zostera marina) is highly dependent on shoot density and pH

Tj. van Heide, A.J.P. Smolders, B. Rijkens, E.H. van Nes, M.M. van Katwijk, J.G.M. Roelofs

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47 Citations (Scopus)


In sheltered, eutrophicated estuaries, reduced nitrogen (NH x ), and pH levels in the water layer can be greatly enhanced. In laboratory experiments, we studied the interactive effects of NH x , pH, and shoot density on the physiology and survival of eelgrass (Zostera marina). We tested long-term tolerance to NH x at pH 8 in a 5-week experiment. Short-term tolerance was tested for two shoot densities at both pH 8 and 9 in a 5-day experiment. At pH 8, eelgrass accumulated nitrogen as free amino acids when exposed to high loads of NH x , but showed no signs of necrosis. Low shoot density treatments became necrotic within days when exposed to NH x at pH 9. Increased NH3 intrusion and carbon limitation seemed to be the cause of this, as intracellular NH x could no longer be assimilated. Remarkably, experiments with high shoot densities at pH 9 showed hardly any necrosis, as the plants seemed to be able to alleviate the toxic effects of high NH x loads through joint NH x uptake. Our results suggest that NH x toxicity can be important in worldwide observed seagrass mass mortalities. We argue that the mitigating effect of high seagrass biomass on NH x toxicity is a positive feedback mechanism, potentially leading to alternative stable states in field conditions.
Original languageEnglish
Pages (from-to)411-419
Issue number3
Publication statusPublished - 2008


  • free amino-acids
  • water-column nitrate
  • false discovery rate
  • ammonium toxicity
  • submersed macrophyte
  • seagrass ecosystems
  • nutritional-status
  • sediment sulfide
  • nh4+ toxicity
  • pine needles


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