The fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrate
نویسندگان
چکیده
In order to determine and understand the stable isotope fractionation of O and N manifested during assimilation of NO−3 in marine macro-benthic algae, two species (Ulva sp. and Agardhiella sp.) have been grown in a wide range of NO−3 concentrations (2–500 μM). Two types of experiments were performed. The first was one in which the concentration of the NO−3 was allowed to drift downward as it was assimilated by the algae, between 24 hour replacements of media. These experiments proceeded for periods of between 7 and 10 days. A second set of experiments maintained the NO−3 concentration at a low steady-state value by means of a syringe pump. The effective fractionation during the assimilation of the NO−3 was determined by measuring the δN of both the (i) new algal growth and (ii) residual NO−3 in the free-drift experiments after 0, 12, 24 and 48 h. Modelling these data show that the fractionation during assimilation is dependent upon the concentration of NO−3 and is effectively 0 at concentrations of less than ∼ 2 μM. The change in the fractionation with respect to concentration is the greatest at lower concentrations (2–10 μM). The fractionation stablizes between 4 and 6 ‰ at concentrations of between 50 and 500 μM. Although the δO and δN values of NO−3 in the residual solution were correlated, the slope of relationship also varied with respect to NO−3 concentration, with slopes of greater than unity at low concentration. These results suggest shifts in the dominant fractionation mechanism of N and O between concentrations of 1 and 10 μM NO−3 . At higher NO − 3 concentrations (> 10–50 μM), fractionation during assimilation will lead to δN values in algal biomass lower than the ambient NO−3 and N enrichments in the residual NO−3 .
منابع مشابه
Nitrate Assimilation: The Role of In Vitro Nitrate Reductase Assay as Nutritional Predictor
Macroalgae or macrophytes are a heterogeneous assemblage of macroscopic eukaryotes belonging to various evolutionary lineages, which live predominantly in aquatic habitats. They have undifferentiated vegetative bodies organized in pseudoparanchymatous and parenchymatous bodies. As with higher plants, marine macroalgae or seaweeds are photosynthetic species that, by harvesting sunlight energy, c...
متن کاملInference of riverine nitrogen processing from longitudinal and diel variation in dual nitrate isotopes
[1] Longitudinal and diel measurements of dual isotope composition (dN and dO) in nitrate (NO3-N) were made in the Ichetucknee River, a large ( 8 m s ), entirely spring-fed river in North Florida, to determine whether isotopic variation can deconvolve assimilatory and dissimilatory removal. Comparing nitrate concentrations and isotope composition during the day and night we predicted (1) daytim...
متن کاملMolybdenum isotope fractionation by cyanobacterial assimilation during nitrate utilization and N2fixation
We measured the δ⁹⁸Mo of cells and media from molybdenum (Mo) assimilation experiments with the freshwater cyanobacterium Anabaena variabilis, grown with nitrate as a nitrogen (N) source or fixing atmospheric N₂. This organism uses a Mo-based nitrate reductase during nitrate utilization and a Mo-based dinitrogenase during N₂ fixation under culture conditions here. We also demonstrate that it ha...
متن کاملStable nitrogen isotope dynamics of dissolved nitrate in a transect from the North Pacific Subtropical Gyre to the Eastern Tropical North Pacific
The stable nitrogen isotopic composition of nitrate, concentrations of inorganic nitrogen and phosphorus, dissolved oxygen and nitrification rates were determined at six stations ranging from the oligotrophic North Pacific Subtropical Gyre (NPSG) to the more productive Eastern Tropical North Pacific (ETNP). Nitrification rates increased along the transect from a maximum rate of 1 nmol L 1 d 1 a...
متن کاملCoupled nitrate N and O stable isotope fractionation by a natural marine plankton consortium
The stable nitrogen (N) and oxygen (O) isotope ratios (15N/14N and 18O/16O, respectively) of nitrate (NO) were measured during incubations of freshly collected seawater to 3 investigate the effect of light intensity on the isotope fractionation associated with nitrate assimilation and possible co-occurring regeneration and nitrification by in situ plankton communities. Surface seawater was coll...
متن کامل