The Effect Of Diurnal Irradiance On Phytoplankton Growth And Primary Production

Phytoplankton exist in lakes,oceans and other natural aquatic environments.It is the player in marine biological pump,which is an important part of the global carbon cycle.It is common to use lab-based experiment to study the dynamics of phytoplankton.An obvious advantage of lab-based study is that an interested or targeted environment factor that modulates phytoplankton growth can be carefully setup and controlled during such lab-based experiment.However,the factitious setting of environment may lead to a difference between the laboratory culture conditions and the nature conditions.If the conclusion obtained by indoor experiments could completely apply to field need to be considered.Light is one of the essential factors for phytoplankton growth through photosynthesis,and there have been many studies on the response of phytoplankton to the light conditions using lab-based experiments.In particular,many experiments used constant light intensity during the day,which is not consistent with the diurnal nature of solar radiation during a day.In order to see if the effect of diurnal light on phytoplankton growth is the same as constant light,we carried out experiments of three species of phytoplankton(Phaeodactylum tricornutum,Skeletonema costatum,Prorocentrum donghaiense xm sp.)with light intensities following diurnal cycles,along with experiments keep constant light intensity,where both setups have the same total light flux during the dat.Further,the experiment used blue light and green light,respectively,to better simulate light quality in natural aquatic environment.It is found that,for the same daily total light flux,all three algal growth rates are higher under constant light condition.Specifically,the growth rate of Phaeodactylum tricornutum under constant light is 25%to 35%higher than that under diurnally varying light,while it is 15%to 45%higher for Skeletonema costatum,and 5%to 10%higher for Prorocentrum donghaiense xm sp.Also,the differences in growth rates are more obvious in the blue light groups than that in the green light groups.In addition,it is found that the specific absorption coefficient of phytoplankton(a*ph)also showed differences between the two types of experimental setups.These results highlight the importance of consistent laboratory setups of such experiments in studying phytoplankton dynamics,otherwise the obtained results or conclusions may not be applicable for phytoplankton in natural environment.