Bacterial biomass production and ammonium regeneration in Mediterranean sea water supplemented with amino acids. 2. Nitrogen flux through heterotrophic microplankton food chain

Abstract

N dynamics effected by bacteria and bacterivorous microflagellates were investigated in a 350 batch experiment. In conditions favoring heterotroph activity (initial amino acid enrichment 100 .mu.g at-N l-1) mineralization rates were, respectively, 2.7 and 10 .mu.g at N-NH4+ l-1 (mg dry wt)-1 h-1 for bacteria and heterotrophic microflagellates. Heterotrophic bacterial community dynamics were investigated by hierarchical classifications, catabolic potentialities and Shannon diversity indexes. Amino acid enrichments favored the development of 2 heterotrophic bacterial communities with complementary physiological roles. One, with growth factor requirements, was able to degrade macromolecules; the other possessed high abilities to use small organic compounds as amino acids. Qualitative composition evolution was correlated to changes in biotic and abiotic parameters.