Differential physiological responses of the coastal cyanobacterium Synechococcus sp PCC7002 to elevated pCO2 at lag, exponential, and stationary growth phases

We studied the effects of expected end-of-the-century pCO(2) (1000 ppm) on the photosynthetic performance of a coastal marine cyanobacterium Synechococcus sp. PCC7002 during the lag, exponential, and stationary growth phases. Elevated pCO(2) significantly stimulated growth, and enhanced the maximum cell density during the stationary phase. Under ambient pCO(2) conditions, the lag phase lasted for 6 days, while elevated pCO(2) shortened the lag phase to two days and extended the exponential phase by four days. The elevated pCO(2) increased photosynthesis levels during the lag and exponential phases, but reduced them during the stationary phase. Moreover, the elevated pCO(2) reduced the saturated growth light (Ik) and increased the light utilization efficiency (alpha) during the exponential and stationary phases, and elevated the phycobilisome: chlorophyll a (Chl a) ratio. Furthermore, the elevated pCO(2) reduced the particulate organic carbon (POC):Chl a and particulate organic nitrogen (PON):Chl a ratios during the lag and stationary phases, but enhanced them during the exponential phase. Overall, Synechococcus showed differential physiological responses to elevated pCO(2) during different growth phases, thus providing insight into previous studies that focused on only the exponential phase, which may have biased the results relative to the effects of elevated pCO(2) in ecology or aquaculture.