Rapid regulation of phosphate uptake in freshwater cyanobacterial blooms

Cyanobacterial blooms are generally explained by nutrient uptake kinetic constants that may confer competitive capabilities, like high nutrient-uptake rate, affinity, and storage capacity. However, cyanobacteria are capable of flexible physiological responses to environmental nutrient fluctuations through adaptation of their phosphate uptake properties. Growth optimization is possible if the physiological reaction time of cyanobacteria (t(R)) matches the duration of nutrient availability. Here, we investigate the t(R) of this complex physiological process. We performed [P-32] uptake experiments with filamentous cyanobacterial blooms. The phytoplankton were subjected to different nutrient exposure times (t(E)) by varying patterns of phosphate additions. After 15 to 25 min of phosphate t(E), the cyanobacteria-dominated phytoplankton began their adaptive response by reducing and finally ceasing uptake activity before exhausting their nutrient uptake capacity. The time of onset of phosphate uptake regulation (in min) is an indicator of tR. Rapid adaptive behaviour may be the initial phase of longer-term nutrient acclimation (hours to days), which results in a higher growth rate. The growth response of bloom-forming cyanobacteria may be more dependent on the ability to optimize the uptake of phosphate during the time span of nutrient fluctuation than on the amount of nutrient taken up per se. Freshwater cyanobacterial blooms may therefore be promoted by their short t(R) during phosphate fluctuations.