Etude comparative de l'absorption de l'azote par deux espèces d'algues rouges : Gracilaria verrucosa (Hudson) papenfuss, 1950 et Gracilaria bursa-pastoris (Gmelin) Silva, 1952

Abstract

To study the ability of two red algae species Gracilaria verrucosa and Gracilaria Bursa-pastoris for their potential use and wastewater treatment, experiments were carried out. The experiments aim to explain the behaviour of these two algae species according to nitrogen form. In the first experiment, we determined the preferential nitrogen form (N-NH sub(4), N-NO sub(3)) for each of the two algae species cultivated separately. We noted that the algae have a clear preference for N-NH sub(4) and that for the same initial concentration. However, G. verrucosa has significantly higher assimilation rate for the two nitrogen forms than G. bursa-pastoris. Thus, identified as algae preferential source, N-NH sub(4) was used under various concentrations, in a second experiment, to check its effect on the rate and velocity of assimilation and the specific growth rate of the two algae species. In the two first culture days and according to the initial concentration, 65 to 75 % of this concentration was absorbed. No significant difference have been observed between the N-NH sub(4) assimilation rates of G. verrucosa and G. bursa-pastoris in the cultures where the initial concentration was lower than 400 mu mol/l. For G. verrucosa, the maximum assimilation rate was obtained in the cultures where the initial N-NH sub(4) concentration was 400 and 500 mu mol/l. On the other hand, G. bursa-pastoris decreased its assimilation rate in the cultures with initial concentration higher than 400 mu mol/l. The specific growth rate average were 2,2 % J super(-1) and 1,5 % J super(-1), respectively, for G. bursa-pastoris and G. verrucosa. Although the latter specie has a more important assimilation rate, G. bursa-pastoris showed a higher specific growth rate. This is due to the fact that G. verrucosa has a N-NH sub(4) storage capacity more important than that of G. bursa-pastoris, which uses the major part of the absorbed N-NH sub(4) for the reconstitution of its cellular structure and for photosynthetic pigments and