Modelling Nitrate Uptake and Nitrite Release by Seaweed

International Journal on Algae 01/2012; 14(2):185-200. DOI: 10.1615/InterJAlgae.v14.i2.60

ABSTRACT The kinetics of nitrate uptake, their assimilation in cell and the kinetics of nitrite release under different initial concentration of nitrates is described with the help of mathematical model The hypothesis of immutability of ferments which take part in transformation of different forms of nitrogen is assumed as a basis of the model. The content of these ferments can be changed only; the induction of their synthesis depends on the initial concentration of nitrates. It is shown that the maximum velocity of nitrate uptake (equal to the activity of nitratereductase) depends on the initial concentration of nitrates and may be presented by hyperbolic function with saturation. It is shown on the example of seaweed Gelidium latifolium (Grev.) Born. et Thur. (Rhodophyta) that the maximum velocity of nitrate absorption can be 5 times more that the initial one.

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    ABSTRACT: The N and P uptake responses were studied in a northern Spanish population of the edible red seaweed Palmaria palmata (Linnaeus) Kuntze. The fronds were incubated at different concentrations, and the nutrient depletion in the medium was measured at successive times to calculate uptake rates. Palmaria palmata uptake response was biphasic and nonsaturable for inorganic P. This would allow the species to exploit transient pulses of high P concentration in natural and fertilized conditions. Such a response is a common feature of algae avoiding nutrient deficiency. At average concentrations measured in the ocean, the response was nonsaturable for inorganic N sources, except for ammonium in autumn and winter when it is not the major N source. In contrast to the general rule of ammonium being taken at a higher rate than nitrate, we found similar affinity for both nutrients corresponding to the minor role of ammonium as N source for field populations over the year.
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    ABSTRACT: The uptake of nitrate, nitrite and ammonium by Codium fragile subsp. tomentosoides (van Goor) Silva was measured at different combinations of temperature (6–30 C) and irradiance (0–140 μEin.m-2. s-1). Uptake of all three forms of N was greater at 12–24 C than at 6 and 30 C. Although uptake was stimulated by light, saturation occurred at relatively low irradiance (7–28 μEin m-2 s-1, depending on the N source and temperature). The Michaelis-Menten uptake constants (Vmax K)varied with temperature. Vmax was greatest at intermediate temperatures and K was lowest at lower temperatures. The Vmaxfor NH4+ was higher and the K, for NH4+was lower than those for NO3-- and NO2--. Codium was capable of simultaneously taking up all three forms of inorganic N although the presence of NH4+ reduced the uptake of both NO3-- and NO2--. The results of this study indicate that part of the ecological success of Codium in a N-limited environment may be due to its N uptake capabilities.
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May 22, 2014