Fijacion de nitrogeno molecular por Trichodesmium ssp. en el mar Caribe: Determinacion experimental del efecto de la irradianza sobre la actividad de la nitrogenasa (Spanish text)

The non-heterocystous N₂ fixing filamentous cyanobacteria Trichodesmium spp. occurs through much of the oligotrophic tropical and sub-tropical marine waters. Tricodesmium spp. are often a major component of the planktonic flora in these systems. As a diazotroph, Trichodesmium may provide significant inputs of new “N” to the euphotic zone, therefore the biogeochemical role of Trichodesmium in the ocean is relevant. Nitrogen fixation by Trichodesmium in the eastern Caribbean region was assayed by the acetylene reduction technique. Etylene production rates were measured at frequent intervals over a daily cycle over 8 months encompassing the season at in maximal activity time at the CaTS station and the Caribbean Sea under different light intensities using the PvsI “photosyntetron” method The average daily maximal of nitrogenase activity “$dPBTmax$” of Tricodesmium was 24.17 ± 14.23 nmol C₂H₄ μg chla −1 h−1. The Maximum fixation rate at the CaTS station was founding in December and March. Considering the circadian rhythm $pBTmax$ and the parameters alfa (αBT) and Eκ, and colonies abundance, the annual input N₂ in the eastern Caribbean is near 1.3 mmol N m−2 year−1.