Photosynthetic characteristics of five high light and low light exposed microalgaea as measured with 14C-uptake and oxygen electrode techniques

#Tetraselmis suecica, #Thalassiosira pseudonana, #Chaetoceros calcitrans, #Isochrysis galbana et #Microcystis sp.$ ont été utilisées pour déterminer leurs capacités d'adaptation et pour tester les différences entre les deux méthodes de mesure. Les cultures avaient été exposées à un éclairement fort (HL) ou à un éclairement faible (LL) pendant deux jours avant l'expérience. L'efficacité de la conversion de la lumière (...) et l'activité photosynthétique spécifique maximale par unité de chlorophylle (...) ont été généralement plus élevées pour les cultures LL. Les divers paramètres photosynthétiques mesurés par la méthode de l'électrode à oxygène ont été différents de ceux obtenus par celle du 14C. Les importantes différences de quotient photosynthétique (O2/CO2), observées aussi bien entre cultures HL et LL d'une même espèce qu'entre espèces différentes, soulignent la difficulté de convertir les productions d'oxygène en assimilation de carbone. (D'après résumé d'auteur

An algorithm to determine primary production in Lake Constance by remote sensing

Any model for aquatic primary production requires the phytoplankton biomass as most important input parameter. However, only the near-surface chlorophyll concentration can be derived from remote sensing data, whereas the vertical distribution of phytoplankton biomass has to be modelled according to the optical properties of the respective water body. Further input parameters that cannot be derived by remote sensing are the parameters of the photosynthesis-light-curve of the involved phytoplankton. Data on the photosynthetic parameters are rare, since measurements are costly and time consuming. However, at Lake Constance a long-term data set exists of primary production measured by the radiocarbon method, and other relevant parameters. This is an ideal data base to develop an algorithm for primary production, since the following issues can be adressed beforehand by data analysis: 1) How can vertical profiles of phytoplankton biomass and production be derived from near-surface chlorophyll considering water temperature and the vertical attenuation coefficient, and 2) what impact does each of the photosynthetic parameters have on the depth integral of photosynthesis? The light saturation parameter Pmax was fairly well predictable by considering the actual water temperature. By contrast, the dependency of the spectrally sensitive parameter alpha on changes in the spectral composition of the incident light could not be satisfactorily described by the existing data set. However, alpha has a major contribution to the depth integral of photosynthesis. Therefore, new measurements of the photosynthetic parameters will be performed by PAM fluorometry to validate the algorithm

Phytoplankton drives nitrite dynamics in the Gulf of Aqaba, Red Sea

This study focuses on the seasonal patterns of nitrite concentration changes and its relationship with phytoplankton activity that is mainly controlled by the alternation of the water column stratification and mixing. Within the euphotic zone during thermal summer stratification, nutrient depletion was severe, and no nitrite could be detected. However, during stratification nitrite was always associated with the nutriclines and formed a deep maximum at the bottom of the euphotic zone. By contrast, within the mixed water column during winter nitrite accumulated, closely following the development of phytoplankton biomass. In the Gulf of Aqaba, the maximum of nitrite accumulation occurred when winter mixing reached its greatest depth, which in turn was coincident with the height of the phytoplankton spring bloom. Thus, our field data suggest that the accumulation of nitrite is associated with nutrient-replete phytoplankton growth. This hypothesis was supported by nutrient enrichment bioassays performed concomitantly: Only when phytoplankton growth was stimulated by nutrient additions, nitrite accumulated in the water. In the bioassays, the time-course of nitrite accumulation closely followed the development of phytoplankton biomass during the incubation period. We therefore suggest that the accumulation of nitrite in the mixed water column during winter was due to the excretion by algal cells. Our field and experimental data show that between 10 to 15 % of the total amount of nitrogen introduced to the mixing water column is released as nitrite by phytoplankton. Further, our field and experimental data support the hypothesis that nitrite excretion by phytoplankton has a significant role in the formation of the DNM during stratification in summer. In the bioassays, phytoplankton cells did excrete nitrite even when ammonia was the nitrogen source. This gives evidence, that there is a so far unrecognised physiological pathway involved in nitrite excretion by phytoplankton cells

Photosynthetic characteristics of five high light and low light exposed microalgaea as measured with 14C-uptake and oxygen electrode techniques

#Tetraselmis suecica, #Thalassiosira pseudonana, #Chaetoceros calcitrans, #Isochrysis galbana et #Microcystis sp.$ ont été utilisées pour déterminer leurs capacités d'adaptation et pour tester les différences entre les deux méthodes de mesure. Les cultures avaient été exposées à un éclairement fort (HL) ou à un éclairement faible (LL) pendant deux jours avant l'expérience. L'efficacité de la conversion de la lumière (...) et l'activité photosynthétique spécifique maximale par unité de chlorophylle (...) ont été généralement plus élevées pour les cultures LL. Les divers paramètres photosynthétiques mesurés par la méthode de l'électrode à oxygène ont été différents de ceux obtenus par celle du 14C. Les importantes différences de quotient photosynthétique (O2/CO2), observées aussi bien entre cultures HL et LL d'une même espèce qu'entre espèces différentes, soulignent la difficulté de convertir les productions d'oxygène en assimilation de carbone. (D'après résumé d'auteur

Biological transfer and sedimentation of Chernobyl radionuclides in Lake Constance

Lindner G, Becker M, Eckmann R, et al. Biological transfer and sedimentation of Chernobyl radionuclides in Lake Constance. In: Tilzer MM, Serruya C, eds. Large lakes - Ecological structure and function. Berlin/Heidelberg: Springer; 1990: 265