The physiological adaptation of the phosphate uptake behaviour of the cyanobacterium Anacystis nidulans (Synechococcus leopoliensis) has been studied under phosphate-deficient conditions. We show that, during additions of pulses of phosphate, the individual cells of a population potentially develop a coherent behaviour with respect to the kinetic and energetic properties of the high-affinity phosphate uptake system. These adaptive responses are independent of the amount of stored phosphate and the absolute external phosphate concentration, but depend on the exposure time to elevated phosphate concentrations. We demonstrate that the response to additions of pulses of phosphate triggers further metabolic alterations to CO2 fixation, and the flow of fixed carbon into the pool of low-molecular weight-compounds or glycogen. These alterations may also affect subsequent growth. The ecological relevance of the adaptive phosphate uptake behaviour is discussed with respect to the establishment and stability of natural communities.