Responses Of Photosynthesis And Carbonic Anhydrase To Environmental Factors In Skeletonema Constatum

In recent years, the diatom bloom occurs frequently in China, and has serious effects on sea fishery and environment. Low CO₂ concentration of surface water has been observed when the algal bloom outbreaks with high cell density. In that time the photosynthetic carbon fixation in diatom strongly depends on the presence of carbonic anhydrase. The occurrence of the diatom bloom is also related with the environmental factors. In this paper, the marine diatom—Skeletonema costatum was selected as experimental materials to investigate its change of the properties of photosynthetic carbon fixation and carbonic anhydrase (CA) activity under different environmental conditions in the laboratory. The main results were as follows:Within the N concentration range from 1 to 200μmol·L^-1, both pH compensation point and plasma membrane redox activity were increased with the elevated N concentrations. When the N concentration was higher than 25μmol·L^-1, the specific growth rate,chl a and chl c contents,light-saturaterd photosynthetic rate (Pm),photosynthetic effiency (α),maximal photochemical efficiency of PSⅡ(Fv/Fm),actual photochemical efficiency of PSⅡ(Yield),photochemical quenching (qP),maximal photosynthetic rate (Vmax),extracellular and intracellular CA activity in S. costatum exhibited a significant increase, but non-photochemical quenching (qN) and the affinity for CO₂ (K0.5) were declined.Within the P concentration range of 0.05^-10μmol·L^-1, both pH compensation point and plasma membrane redox activity had an obvious rise with the increasing P concentrations. The P concentration higher than 1μmol·L^-1 resulted in an increase in the specific growth rate,chl a and chl c contents,Pm,α,Fv/Fm,Yield,Vmax,extracellular and intracellular CA activity, while the decrease in qN was observed in S. costatum.Within the Fe concentration range from 0.1 to 100nmol·L^-1, pH compensation point and plasma membrane redox activity were elevated with the increasing Fe concentrations. The specific growth rate,chl a and chl c contents,Pm,α,Fv/Fm,Yield,qP,Vmax,extracellular and intracellular CA activity were increased, while K0.5 was declined when the alga was exposed to Fe concentration higher than 50nmol·L^-1.Within the Si concentration range of 1-200μmol·L^-1, the specific growth rate, P_m,αand V_maxwere not signifcantly affected, whereas pH compensation point and plasma membrane redox activity were slightly increased with the rise of Si concentrations. The rise of chl a and chl c contents,extracellular CA activity and K0.5 were found when the alga was grown in the Si concentration higher than 1μmol·L^-1.pH compensation point, plasma membrane redox activity, Vmax, the affinity for CO₂ and extracellular CA activity in air-grown cells had an obvious increase relative to high-CO₂-grown cells in light. The darkness also resulted in the increase in plasma membrane redox activity, Vmax and the affinity for CO₂, but no change in pH compensation point and extracellular CA activity in air-grown cells.All the results above suggested that the algae adapted to different N, P, Si, Fe environment by means of regulating the affinity for CO₂,carbonic anhydrase activity and the energy flow and energy use efficiency of PSⅡ. The characteristics of the use of inorganic carbon and extracellular CA activity could be also affected by CO₂ and light.