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

Abstract

We studied the effects of expected end-of-the-century p CO2 (1000 ppm) on the photosynthetic performance of a coastal marine cyanobacterium Synechococcus sp. PCC7002 during the lag, exponential, and stationary growth phases. Elevated p CO2 significantly stimulated growth, and enhanced the maximum cell density during the stationary phase. Under ambient p CO2 conditions, the lag phase lasted for 6 days, while elevated p CO2 shortened the lag phase to two days and extended the exponential phase by four days. The elevated p CO2 increased photosynthesis levels during the lag and exponential phases, but reduced them during the stationary phase. Moreover, the elevated p CO2 reduced the saturated growth light (Ik) and increased the light utilization efficiency ( α ) during the exponential and stationary phases, and elevated the phycobilisome:chlorophyll a (Chl a ) ratio. Furthermore, the elevated p CO2 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 p CO2 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 p CO2 in ecology or aquaculture.