title: Seasonal variations in nitrate reductase activity and internal N pools in intertidal brown algae are correlated with ambient nitrate concentrations.
abstract: Nitrogen metabolism was examined in the intertidal seaweeds Fucus vesiculosus, Fucus serratus, Fucus spiralis and Laminaria digitata in a temperate Irish sea lough. Internal NO(3) (-) storage, total N content and nitrate reductase activity (NRA) were most affected by ambient NO(3) (-), with highest values in winter, when ambient NO(3) (-) was maximum, and declined with NO(3) (-) during summer. In all species, NRA was six times higher in winter than in summer, and was markedly higher in Fucus species (e.g. 256 +/- 33 nmol NO(3) (-) min(-1) g(-1) in F. vesiculosus versus 55 +/- 17 nmol NO(3) (-) min(-1) g(-1) in L. digitata). Temperature and light were less important factors for N metabolism, but influenced in situ photosynthesis and respiration rates. NO(3) (-) assimilating capacity (calculated from NRA) exceeded N demand (calculated from net photosynthesis rates and C : N ratios) by a factor of 0.7-50.0, yet seaweeds stored significant NO(3) (-) (up to 40-86 micromol g(-1)). C : N ratio also increased with height in the intertidal zone (lowest in L. digitata and highest in F. spiralis), indicating that tidal emersion also significantly constrained N metabolism. These results suggest that, in contrast to the tight relationship between N and C metabolism in many microalgae, N and C metabolism could be uncoupled in marine macroalgae, which might be an important adaptation to the intertidal environment.
authors.affiliation: School of Biological Sciences, Queens University of Belfast, Lisburn Road, Belfast, Northern Ireland, UK. ebyoung@uwm.edu
authors.forename: Erica B
authors.initials: EB
authors.lastname: Young
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Dring
authors.forename: Graham
authors.initials: G
authors.lastname: Savidge
authors.forename: Daryl A
authors.initials: DA
authors.lastname: Birkett
authors.forename: John A
authors.initials: JA
authors.lastname: Berges
mesh_terms: D050901:Nitrate Reductase / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D000459:Phaeophyceae / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology; D010788:Photosynthesis; D012621:Seasons; D013045:Species Specificity
chemical_list: D009566:Nitrates; D050901:Nitrate Reductase