Effect of light intensity on the photosynthetical responses of Gracilaria lemaneiformis in non-aerated and aerated cultures

The economic red macroalga Gracilaria lemaneiformis was selected to study light intensity effects on its growth,photosynthesis,effective quantum efficiencies(Yield)and pigments contents in aerated and non-aerated cultures.Three different light intensities were as follows:50 μmol/(m²·s)(low light intensity),100 μmol/(m²·s)(moderate light intensity),and 200 μmol/(m²·s)(high light intensity).The results showed that the highest growth rate of G.lemaneiformis was observed when alga was treated with moderate light intensity,and too low or too high light intensity inhibited its growth.The relative growth rates of aerated cultured algae,under the low light intensity,moderate light intensity and high light intensity,were increased by 26.85%,31.82% and 40.56%,respectively.In aerated culture,the photosynthetic rate and the photosynthetic efficiency of alga treated with low light intensity increased by 8.14% and 4.26%,and the respiration rate of alga under high light intensity decreased by 20.70%,and Yield increased by 44.16%.The results suggested that reduced growth was mainly due to the limited photosynthesis in case of low light intensity,or could be ascribed to the increased respiration in case of high light intensity.Aerated culture could relieve the negative effect on the growth rate of alga as a result of for low light or high light intensity.