COMPETITION FOR PHOSPHORUS BETWEEN THE NITROGEN-FIXING CYANOBACTERIA ANABAENA AND APHANIZOMENON

The influence of Na fixation on the P-limited growth of two strains of Anabaena and Aphanizomenon was investigated using continuous cultures . Under N-2-fixing conditions Anabaena had a higher maximum growth rat e, a greater affinity for P, a higher yield on P and a higher N-2 fixa tion activity than Aphanizomenon. In contrast to Anabaena, Aphanizomen on did not adjust its specific N-2 fixation activity and its cells bec ame N depleted at high growth rates. Metabolic control analysis reveal ed that the growth rate of Aphanizomenon was controlled to a lesser ex tent by P than Anabaena's growth rate. As predicted on the basis of th ese monoculture measurements, Anabaena was the superior competitor for P in competition experiments. The results might help to distinguish t he niches of these two closely related species.