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

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.

Bibliographic Details

Main Authors:	van Heide, Tj., Smolders, A.J.P., Rijkens, B., van Nes, E.H., van Katwijk, M.M., Roelofs, J.G.M.
Format:	Article/Letter to editor biblioteca
Language:	English
Subjects:	ammonium toxicity, false discovery rate, free amino-acids, nh4+ toxicity, nutritional-status, pine needles, seagrass ecosystems, sediment sulfide, submersed macrophyte, water-column nitrate,
Online Access:	https://research.wur.nl/en/publications/toxicity-of-reduced-nitrogen-in-eelgrass-zostera-marina-is-highly
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