Nitrogen status and metabolism in the green seaweed Enteromorpha intestinalis: an examination of three natural populations

Abstract

Nitrogen metabolism in Enteromorpha intestinalis from 3 contrasting populations in the Auckland region, New Zealand, was investigated. The sites (intertidal flats at Laingholm in the Manukau Harbour and Mangemangeroa and rockpools at Waterfall Reef) were chosen as they provided a range of ammonium enrichment. Seawater at Laingholm had higher levels of ammonium and total inorganic nitrogen compared with the other 2 sites. However, mean nitrate levels in Mangemangeroa seawater were similar to those measured at Laingholm. Seawater at Waterfall Reef had the lowest concentrations of ammonium and nitrate. At all 3 sites, E. intestinalis was found high in the intertidal. At Laingholm, the ammonium-enriched site, plants were immersed for 90 min at high tide; during this period the plants took up sufficient ammonium to increase their nitrogen content by 10%. The higher levels of inorganic nitrogen in the seawater at Laingholm resulted in higher levels of tissue nitrogen, chl a and b, glutamine and asparagine, and lower nitrogen-specific rates of ammonium assimilation (measured in the laboratory in the presence of saturating concentrations of ammonium) in E. intestinalis at this site. There were strong positive correlations between seawater concentrations of ammonium and the level of glutamine and between levels of chl a and b and tissue nitrogen in E. intestinalis. The nitrogen-specific rate of ammonium assimilation decreased as the nitrogen content of the plant increased and reached a minimum value above a nitrogen content of 1 to 2% or a glutamine level of 5 µmol per g dry weight (DW). This glutamine level corresponded to a seawater ammonium concentration of 6 µM. The nitrogen-specific rate of ammonium assimilation provides a novel and important bioindicator of the link between the concentration of inorganic nitrogen in the environment and the nitrogen status of the plant.

Supply- and demand-driven phosphate uptake and tissue phosphorus in temperate seaweeds

“…Seawater samples were stored frozen (−18°C) and unfiltered until analysis. Independent experiments verified that this procedure had no effect on the results obtained and that there was no significant difference in nutrient concentrations between filtered and unfiltered seawater samples (Barr & Rees 2003). A problem that we have encountered (specifically with nitrite) is that filtering introduces contamination (B. C. Dobson unpubl.)…”

“…Our unpublished data show peaks in tissue nitrogen in June for 2 of the species (U. intestinalis and Xiphophora chondrophylla) used here. It should be noted that this nitrogen may be stored as a variety of different compounds from chlorophyll-protein complexes in green algae (Barr & Rees 2003), L-citrullinyl-Larginine and/or gigartinine in red algae (Laycock & Craigie 1977) to specific storage proteins in brown algae (Pueschel & Korb 2001), but that all of these need to be metabolised to provide the amino acids required for the synthesis of proteins associated with growth. This protein synthesis generates an increase in demand-driven uptake of phosphate, which is required mainly for the synthesis of RNA, in particular ribosomal RNA (Sterner & Elser 2002).…”

Influência da disponibilidade de nitrato sobre crescimento, atividade da nitrato redutase, composição química e captação de nitrato e fosfato em Gracilariopsis tenuifrons (Gracilariales, Rhodophyta)

“…Ao contrário, em condições de alta disponibilidade de nitrogênio o conteúdo de carbono diminui em resposta à assimilação do nitrogênio (García-Sánchez et al, 1993;. Portanto, a razão entre carbono e nitrogênio tecidual é um parâmetro associado à nutrição em longo prazo (Barr & Rees, 2003).…”

“…A razão C:N é um parâmetro associado à nutrição em longo prazo e usado em modelos de produtividade primária (Geider & La Roche, 2002;Barr & Rees, 2003). A razão de Redfield, que define uma relação fixa C:N para o plâncton marinho de 106:16 (aproximadamente 6,06), tem sido contestada por diversos trabalhos, os quais afirmam que a razão C:N varia de acordo com a espécie e com as condições nutricionais a que os organismos estão submetidos (Geider & La Roche, 2002;Ho et al, 2003).…”

“…Isto poderia indicar que, nesta situação, o crescimento não refletiria o balanço entre o metabolismo do carbono e do nitrogênio e que a razão C:N ainda seria um bom indicador do estado nutricional de Gp. tenuifrons (Barr & Rees, 2003).…”