Inorganic nitrogen uptake by two kelp species, Laminaria solidungula and Laminaria saccharina, in the Alaskan High Arctic
The uptake of inorganic nitrate (NO₃⁻) and ammonium (NH₄⁺) by two co-occurring species of kelp, Laminaria solidungula and Laminaria saccharina, was compared using entire plants incubated under natural conditions in the field and in the laboratory. Field experiments were conducted in situ during ice-...
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| Format: | Thesis |
| Language: | English |
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1995
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| Online Access: | https://hdl.handle.net/2152/120730 https://doi.org/10.26153/tsw/47563 |
| Summary: | The uptake of inorganic nitrate (NO₃⁻) and ammonium (NH₄⁺) by two co-occurring species of kelp, Laminaria solidungula and Laminaria saccharina, was compared using entire plants incubated under natural conditions in the field and in the laboratory. Field experiments were conducted in situ during ice-covered and open-water periods in the Boulder Patch kelp bed community in the Alaskan Beaufort Sea. The data obtained in these experiments do not provide evidence of Michaelis-Menten saturation kinetics. The uptake of NO₃⁻ and NH₄⁺ by both species appears to be a linear function of substrate concentration with no evidence of a saturating concentration although average substrate concentrations approach 80 μM. There was no significant difference between NO₃⁻ and NH₄⁺ uptake rates in conditions where either NO₃⁻ or NH₄⁺ were supplied at the same concentrations and no significant difference in uptake rates between species. The mean uptake rate at ambient nitrate concentrations in winter (4 - 7 μM) was 0.53 /μmoles gdw⁻¹h⁻¹. Uptake rate values obtained by substrate disappearance at ambient concentrations were corroborated by measurements of ¹⁵N stable isotope incorporation. Dark and light-exposed plants of both species also exhibited equivalent rates of uptake in short-term experiments with either NO₃⁻ or NH₄⁺ present as substrate. L. solidungula also demonstrated equal dark/light uptake with both nitrogen substrates present, revealing no competitive inhibition of either substrate. Time course disappearance for L. solidungula with NO₃⁻ or NH₄⁺ and NO₃⁻/NH₄⁺ followed second order kinetics. Water motion was shown to significantly enhance both NO₃⁻ and NH₄⁺ disappearance for L. solidungula. Linear growth rates in juvenile L. solidungula sporophytes were not affected by NO₃⁻ concentration, but this may be related to the translocation of organic nitrogen to support linear growth at low NO₃⁻ concentrations, based on the bleaching of distal blade tissues in nitrogen-starved plants. The nitrogen uptake rates determined in this ... |
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