Interactions of light and inorganic nitrogen in controlling nitrogen uptake in the sea

Upon addition of inorganic nitrogen to phytoplankton in various nutritional states, transient changes in net carbon uptake were observed over a few hours in daylight, both in euphotic zone profiles and in time series of natural and cultured samples. The reductions in carbon fixation, probably due to increased respiration, led to inverse relations between carbon and nitrogen uptake. They were sometimes followed by stimulations of carbon uptake, corresponding or not to exhaustion of the added nutrient. Such phenomena could not be readily interpreted in terms of nutrient deficiency, as they also occurred in waters in which dissolved nitrogen compounds were around 3 PM. Under controlled laboratory conditions, interspecific variability in responses of the carbon uptake system to a nitrogen addition was very high, but the absolute irradiance level appeared to be determinant in the manifestation of such patterns.

Section: Discussionsupporting

confidence: 62%

“…In contrast, others (Morris et al, 1971;Yentsch et al, 1977;MacIsaac et al, 1979;Goldman et al, 1981;Goldman and Dennett, 1983) found no effect at all. Finally, some investigators reported varying responses in different situations (MacIsaac and Dugdale, 1972;Lean et al 1982).…”

Section: Discussionmentioning

confidence: 99%

13C and 15N uptake by marine phytoplankton. Ill Interactions in euphotic zone profiles of stratified oceanic areas

Collos¹,

Slawyk²

1984

“…Negative fluxes might indicate uptake of ammonium by the enclosed plankton and benthos and nitrification in the upper mm's of sediment or overlying waters. Opaque chambers would minimize but not prevent ammonium uptake by primary producers (MacIsaac & Dugdale 1972, Hanisak 1984. The occurrence of lower-than-predicted fluxes suggests, in addition to benthic uptake or overestimation of ammonification, that the ammonium produced could be lost to nitrification, possibly coupled to denitrification.…”

Section: Discussionmentioning

confidence: 99%

Ammonium distributions, production, and efflux from backreef sediments, St. Croix, US Virgin Islands

Williams¹,

Yarish²,

Gill³

1985

Sediments in < 3 m water depth on Tague Bay backreef, St. Croix, US Virgin Islands, were sampled for grain size, Eh, pH, organic carbon, pore-water ammonium and nitrate + nitrite concentrations, ammonium production, and ammonium and nitrate + nitrite benthic fluxes. Most sampling sites had nutrient-poor, oxidized, coarse sand-sized sediments. Ammonium and nitrate + nitrite concentrations were typically < 5 PM; organic carbon was < 0.6 % g dry weight. High spatial heterogeneity on the scale of cm2 existed in all parameters measured except grain size, which decreased regularly away from the reef. We suggest that the nutrient-poor conditions were maintained by high turbulence in the environment, which would minimize organic input to the sediments and maximize resuspension and oxygenation. This view was supported by ammonification rates (mean = 70 pm01 (1 sediment)-' d-l) and benthic nitrogen fluxes which were low compared to rates reported from many temperate coastal areas. Benthic nitrogen fluxes were highly variable and averaged ?l f 95 (mean + SD) w o l ammonium m-* d-I and -5 f 40 pm01 nitrate + nitrite m-2 d-l. Local pockets of reducing sediments with ammonium concentrations > 30 occurred within the generally low-nutrient environment. Their location was correlated in part to stabilization of sediments by certain benthic microalgae. These areas may be zones of enhanced nitrogen remineralization, benthic nitrogen f l u e s , and possibly nitrification coupled to denitrification. Comparison of the range of fluxes predicted from ammonification data to the range of measured fluxes showed both positive and negative deviations. Nitrification coupled to denitrification cannot be ruled out as an explanation for measured fluxes which were lower than the production-predicted f l u e s because Eh and pH conditions were within the environmental limits of denitrifying organisms. Loss of nitrogen via denitrification would be an important process to verify in coral reef ecosystems where conservation of nitrogen apparently is otherwise maximized.

“…Our results for NO; and urea demonstrate their dependency of uptake on light and in this respect both nutrients are comparable. The light dependence of uptake of both nutrients is well established (MacIsaac & Dugdale 1972, Mitamura & Saijo 1975, 1980, Webb & Haas 1975, Hawey & Caperon 1976, Nelson & Conway 1979. Other reports have shown that nitrogen-deprived phytoplankton have higher dark uptake rates of nitrogen than nitrogen-replete phytoplankton (e.g.…”

Section: Simultaneous Uptake Of Nitrogen Compoundsmentioning

confidence: 97%

Time course of uptake of inorganic and organic nitrogen by phytoplankton in the Strait of Georgia: comparison of frontal and stratified communities

Price¹,

Cochlan²,

Harrison³

1985

In both frontal and stratified water of the Strait of Georgia, changes in dissolved nitrogen concentrations provided evidence for the simultaneous uptake of ammonium, nitrate and urea by a summer phytoplankton community. Chlorophyll a specific uptake rates of ammonium and urea were ca 2 and 2.4 times greater in stratified water than in frontal water, whereas chlorophyll a specific nitrate uptake rates were ca 1.6 times greater in frontal water. Ammonium and urea regeneration rates, calculated using a mass balance approach, were similar in frontal water, but urea regeneration rates were 2 to 5 times greater in the stratified water during the first 12 h of the experiment. Increases in particulate nitrogen could not be accounted for by corresponding decreases in total concentration of dissolved inorganic nitrogen and urea, or by 15N accumulation in the particulates. In frontal water the change in total dissolved inorganic nitrogen and urea consistently overestimated the change in particulate nitrogen, and in stratified water the change in total dissolved inorganic nitrogen and urea consistently underestimated the change in particulate nitrogen. These data suggest that the plankton community In frontal water was losing nitrogen in the form of dissolved organic nitrogen. By contrast, the plankton community in stratified water took up nitrogen compounds which were not measured as part of the total dissolved inorganic and urea nitrogen, but were most likely dissolved organic nitrogen compounds. Results stress the importance of determining uptake rates of all 3 nitrogen substrates (NHfi, N O and urea) using 15N isotopes and by simultaneously measuring the change in concentration of these compounds throughout the incubation period.