Bibliography on CO2 Effects on Vegetation and Ecosystems: 1990-1999 Literature

Over a period of several days, rhythmic changes in extracellular NH4+ concentration take place in cultures of the cyanobacterium Microcystis firma (Breb et Lenorm.) Schmidle, strain Gromov/St. Petersb. 398, under conditions of restricted CO2 supply and light/dark alternation. The changes are enhanced by nitrate supply. Among the various processes generating intracellular NH4+ (NH4+ uptake, NO3reduction, protein and amino acid degradation, photorespiration), NO3reduction appears as the one most important. This can be concluded from experiments with and without nitrate and/or ammonium in the medium. In the presence of saturating CO2, continuous light, or continuous darkness, rhythmic NH4+ oscillations are not induced. Studies of the incorporation of NH4+ nitrogen by in vivo N-15-NMR show that if CO2 is supplied, N-15 is accumulated in several components with the following time course: in the first hour in Gln (delta), in the second hour in the alphaamino groups of most nonbranched amino acids, in the third hour in gammaaminobutyric acid (GABA), Orn (delta) and Lys (epsilon), and in the sixth hour in Ala. Carbon limitation, however, results in accumulation of label in the amide nitrogen of glutamine only.