Effects of inorganic carbon supplies and light on photosynthetic functions of Pyropia haitanensis.

Abstract

The increasing stocking density of algal often results in lowered carbon and light levels. In this study, Pyropia haitanensis were cultured under four different conditions, i.e., 390 μL·L-1 (ambient carbon supply) + ambient sunlight, 20 μL·L-1(decreased carbon supply) + ambient sunlight, 390 μL·L-1 + decreased sunlight (20% of ambient sunlight), 20 μL·L-1 + decreased sunlight. The activity of carbonic anhydrase (CA), photosynthetic rate and quantum efficiency of open photosynthetic system 2 (Fv'/Fm') of the algae under different temperatures were measured to investigate the effects of decreased carbon supply and lowered light on photosynthetic functions of P. haitanensis. The results showed the CA activities of the algae at decreased carbon supply and lowered sunlight was increased. The maximum Ci-saturated photosynthetic rates (Vmax) were elevated under the low sunlight compared with that under the ambient sunlight. The Vmax of the algae at low carbon seawater was lower than that at ambient carbon seawater under lowered sunlight. Under ambient sunlight, the Vmax of the decreased carbon-grown algae was higher than that of ambient carbon-grown algae. The Fv'/Fm' values of the algae grown at lowered carbon supply and decreased sunlight conditions showed no variation at low temperature (10 ℃) and high temperature (30 ℃), whereas it was decreased by about 76.4% when cultured at 390 μL·L-1 + ambient sunlight at 200 min than that at 40 min under 30 ℃. These results suggested that decreased carbon supply and lowered sunlight intensity would improve in the capacity of HCO3- utilization and resistance to short-term temperature change in P. haitaneisis. The effects of low carbon on photosynthetic rate of the algae were dependent on light context.