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

Figures & data

Fig. 1–4 Uptake rates (µmol cm⁻² h⁻¹) for Heminura frondosa as a function of increasing NO₃^– concentration (µM) for algae acclimated to either (1) saturating irradiance (150 µmol photons m⁻² s⁻¹) and (2) limiting irradiance (30 µmol photons m⁻² s⁻¹) and NH₄⁺ under (3) saturating irradiance (150 µmol photons m^–2 s^–1) and (4) limiting irradiance (30 µmol photons m⁻² s⁻¹). Solid lines indicate regression of best fit. Note that the y-axis range for graphs 1 and 2 are different to those of 3 and 4. Each symbol represents an individual macroalgal replicate (n = 5)

Fig. 5. Soluble tissue NO₃⁻ and NH₄⁺ concentrations (µmol g WW⁻¹) from Heminura frondosa individuals acclimated to saturating (150 µmol photons m⁻² s⁻¹) and limiting (30 µmol photons m⁻² s⁻¹) irradiance. Bars represent mean ± SE, n =10, * = p < 0.05 (Wilcoxon rank sum test)

Fig. 6–7. Photosynthetic pigment content of Heminura frondosa (mg g WW⁻¹) acclimated to saturating (150 µmol photons m⁻² s⁻¹) and limiting (30 µmol photons m⁻² s⁻¹) irradiance (6) PE and (7) Chl a. Bars represent mean ± SE, n =10, * = p < 0.05 (Wilcoxon rank sum test)

Fig. 8. NR activity (μmol NO₃⁻ reduced min^–1 g WW^–1) from Heminura frondosa acclimated under saturating (150 µmol photons m⁻² s⁻¹) and limiting (30 µmol photons m⁻² s⁻¹) irradiance. Bars represent mean ± SE, n = 10

Fig. 9–11. Tissue carbon (9) and nitrogen content (10) expressed as %DW, and C:N ratio (11), for Heminura frondosa acclimated to saturating (150 µmol photons m⁻² s⁻¹) and limiting (30 µmol photons m⁻² s⁻¹) irradiance. Bars represent mean ± SE, n = 4, * = p < 0.05 (Wilcoxon rank sum test)