The impact of irradiance on optimal and cellular nitrogen to phosphorus ratios in phytoplankton

Jan Erik Thrane*, Dag O. Hessen, Tom Andersen, Helmut Hillebrand (Editor)

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Citations (Scopus)
13 Downloads (Pure)


Phytoplankton acclimates to irradiance by regulating the cellular content of light-harvesting complexes, which are nitrogen (N) rich and phosphorus (P) poor. Irradiance is thus hypothesised to influence the cellular N : P ratio and the N : P defining the threshold between N and P limitation (the ‘optimal’ N : P). We tested this hypothesis by first addressing the response of the optimal N : P to irradiance in a controlled experiment with Chlamydomonas reinhardtii. Then, we did a meta-analysis of experimental data on optimal and cellular N : P ratios across light gradients to test the generality of an N : P to light response within species. In both the experiment and the meta-analysis, N : P ratios decreased with irradiance, indicating that factors affecting underwater irradiance, like depth and the composition of the water, may influence the relative N : P requirement. The effect of irradiance did not differ between optimal and cellular N : P ratios, but observations of optimal N : P were on average 2.8 times higher than observations of cellular N : P.

Original languageEnglish
Pages (from-to)880-888
Number of pages9
JournalEcology Letters
Issue number8
Publication statusPublished - 1 Aug 2016
Externally publishedYes

Bibliographical note

Copyright the Author(s) 2016. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


  • Chlamydomonas
  • reinhardtii
  • ecological stoichiometry
  • irradiance
  • light
  • N : P ratio
  • nitrogen
  • optimal N : P
  • phosphorus
  • Redfield ratio


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