title: Effects of nitrogen supply on Pseudo-nitzschia calliantha and Pseudo-nitzschia cf. seriata: field and laboratory experiments.
abstract: The effects of inorganic and organic nitrogen supply on the growth and domoic acid (DA) production of Pseudo-nitzschia cf. seriata and Pseudo-nitzschia calliantha from Bizerte Lagoon (SW Mediterranean Sea) were studied during field and laboratory experiments. Nitrogen enrichments (40 µM NO3 (-); 10 µM NH4 (+); 20 µM CH4N2O) and a control, with no added N, were carried out in separate carboys with seawater collected from Bizerte Lagoon. In the field experiments, all N-enrichments resulted in significant increases in chlorophyll a concentration, and maintained exponential growth until the end of the experiment. The initial diatom community was dominated by a bloom of P. cf. seriata (9.3 × 10(5) cells l(-1)). After 6 days of incubation, the abundance of P. cf. seriata was greatest in the urea addition (1.52 × 10(6) cells l(-1)), compared to the ammonium treatment (0.47 × 10(6) cells l(-1)), nitrate treatment (0.70 × 10(6) cells l(-1)) and control (0.36 × 10(6) cells l(-1)). The specific growth rates, calculated from increases in chlorophyll a and cell abundance, were statistically different across all treatments, with the highest in the urea and nitrate additions. Similar results were obtained from the laboratory experiments. These were carried out with P. calliantha isolated from Bizerte Lagoon and grown in f/2 medium enriched with 40 µM nitrate, 10 µM ammonium and 20 µM urea. The exponential growth rate was significantly faster for the cells cultured with urea (1.50 d(-1)) compared to the nitrate (0.90 d(-1)) and ammonium (0.80 d(-1)) treatments and the control (0.40 d(-1)). Analysis of DA, performed at the beginning and the end of the both experiments in all treatments, revealed very low concentrations (below the limit of quantification, 0.02- 1.310(-7) pg cell(-1), respectively).The field and laboratory experiments demonstrate that P.cf. seriata and P. calliantha are able to grow efficiently on the three forms of N, but with a preference for urea.
authors.affiliation: Laboratoire de Phytoplanctonologie, Faculté des Sciences de Bizerte, Université de Carthage, Bizerte, Tunisia. sondesgarali@yahoo.fr.|Institut Supérieur de Pêche et d'Aquaculture de Bizerte, B.P.15.7080, Errimel, Bizerte, Tunisia. sondesgarali@yahoo.fr.
authors.forename: Sondes
authors.initials: S
authors.lastname: Melliti Ben Garali
authors.affiliation: Laboratoire de Phytoplanctonologie, Faculté des Sciences de Bizerte, Université de Carthage, Bizerte, Tunisia.
authors.forename: Inès
authors.initials: I
authors.lastname: Sahraoui
authors.affiliation: Institut de Recherche et Technologie Agroalimentaire (IRTA), Ctra. Poble Nou, Km 5.5, Sant Carles de la Rapita, 43540, Tarragona, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: de la Iglesia
authors.affiliation: Institut Supérieur de Pêche et d'Aquaculture de Bizerte, B.P.15.7080, Errimel, Bizerte, Tunisia.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Chalghaf
authors.affiliation: Institut de Recherche et Technologie Agroalimentaire (IRTA), Ctra. Poble Nou, Km 5.5, Sant Carles de la Rapita, 43540, Tarragona, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Diogène
authors.affiliation: Institut Supérieur de Pêche et d'Aquaculture de Bizerte, B.P.15.7080, Errimel, Bizerte, Tunisia.
authors.forename: Jamel
authors.initials: J
authors.lastname: Ksouri
authors.affiliation: Laboratoire de Phytoplanctonologie, Faculté des Sciences de Bizerte, Université de Carthage, Bizerte, Tunisia.
authors.forename: Asma
authors.initials: A
authors.lastname: Sakka Hlaili
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D017377:Diatoms / Q000502:physiology*; D007608:Kainic Acid / Q000031:analogs & derivatives; D008387:Marine Toxins; D008522:Mediterranean Sea; D009566:Nitrates; D009584:Nitrogen / Q000633:toxicity*; D012623:Seawater / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D008387:Marine Toxins; D009566:Nitrates; D014874:Water Pollutants, Chemical; D002734:Chlorophyll; C012301:domoic acid; D009584:Nitrogen; D007608:Kainic Acid; D000077194:Chlorophyll A
keywords: Domoic acid; Harmful algae; Nitrogen; Pseudo-nitzschia; Urea