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Light regulates inorganic nitrogen uptake and storage, but not nitrate assimilation, by the red macroalga Hemineura frondosa (Rhodophyta)

Paine, ER, Schmid, M, Revill, AT and Hurd, CL ORCID: 0000-0001-9965-4917 2020 , 'Light regulates inorganic nitrogen uptake and storage, but not nitrate assimilation, by the red macroalga Hemineura frondosa (Rhodophyta)' , European Journal of Phycology , pp. 1-12 , doi: 10.1080/09670262.2020.1786858.

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Abstract

Macroalgal growth in temperate coastal ecosystems is primarily regulated by light and inorganic nitrogen availability. The effect of light (photon irradiance) on NO3 − and NH4 + uptake, and NO3 − assimilation, were studied in the red macroalga, Hemineura frondosa, which does not operate a carbon concentrating mechanism (non-CCM). Non-CCM macroalgae grow in low and high light environments but become increasingly dominant with depth, suggesting a mechanism for ‘preserving energy’ under low light levels. H. frondosa was acclimated to limiting (30 µmol photons m− 2 s− 1) and saturating (150 µmol photons m− 2 s–1) irradiances for 8 days. Then, NO3 − and NH4 + uptake rates were measured under limiting and saturating irradiances at six concentrations ranging from 2–64 μM. NO3 − uptake did not follow saturating uptake kinetics at both irradiances suggesting multiple uptake mechanisms. NH4 + uptake saturated at concentrations 3 − and NH4 +. There was no evidence that irradiance regulated NO3 − reduction by nitrate reductase. Also illustrated is the importance of measuring nitrate reductase activity on fresh material, as freezing in liquid nitrogen and storage at −80°C for 7 days caused a 65% decline in activity. Photosynthetic pigments, soluble tissue nitrogen and % total tissue nitrogen were all higher in limiting irradiance. In this first study of the nitrogen physiology of a non-CCM seaweed, we show that light regulates NO3 − and NH4 + uptake but not NO3 − assimilation.

Item Type: Article
Authors/Creators:Paine, ER and Schmid, M and Revill, AT and Hurd, CL
Keywords: red seaweed, algae, nitrogen uptake, nitrogen reductase
Journal or Publication Title: European Journal of Phycology
Publisher: Taylor & Francis Ltd
ISSN: 0967-0262
DOI / ID Number: 10.1080/09670262.2020.1786858
Copyright Information:

Copyright 2020 British Phycological Society

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