The Effects Of Different Light Intensities On Photosynthetic Characteristics Of Skeletonema Costatum During Rejuvenation

The sediments in the offshore sea had a large amount of diatom cells.These cells are generally considered dormant.Once sediments resuspending due to the upwelling or bioturbation,the resting stage cells would rejuvenate in the suitable environment.Some diatom species may cause blooms.Resting stage,rejuvenation and vegetative growth of diatoms are affected by various factors.Light is the energy resource and both an essential "switch" that induced the rejuvenation of the resting stage cells in the diatoms.Therefore,we mainly studied on photosynthetic activity of vegetative growth and rejuvenation of the typical blooms diatom species Skeletonema costatum in different light intensities.The optimal light intensity of resting stage cells rejuvenation is explained.We attempt to explain how the rejuvenated resting stage cells could gain an advantage in competition with other phytoplankton,even result in blooms.In this study,we investigated the effects of different light intensities(50,150,250,350 ?mol·m-2·s-1)on physiological and ecological characters of S.costatum(50,150,250,350 ?mol·m-2·s-1)in the process of rejuvenation.Growth factors(cell density.nutrient absorption)and photosynthetic parameters of the algae were evaluated.Photosynthetic parameters include the ratio of variable to maximal chlorophyll fluorescence(Fv/Fm),chlorophyll a(Chi a),initial slope of the ETR versus Ecurve(a),maximal electron transport rate(ETRmax)and saturation light intensity(Ik).The main results of the study were showed as follow:(1)At a certain light intensity range,for S.costatum vegetative cells growth,under the light intensity of 50?mol·m-2·s-1,cells had the highest photosynthetic activity,vigorous growth and rapid proliferation of cells.The cell count of 50?mol·m-2·s-1 was 116×104/mL,was 37.25%,67.05%,59.03%higher than other three respectively.When the cells are exposed to the light intensities of 250 and 350?mol·-2·s-1,the growth of vegetative cells was inhibited.The optimal light intensity of vegetative growth is 50?mol·m-2·s-1.(2)Low temperature and dark treatments to S.costatum(50 ?mol·m-2·s-1),photosynthetic activity of the cells decreased with time.The cells of S.costatum after twenty days dark treatments cannot be detected for photosynthetic characteristics(Fv/Fm,a,ETRmax and Ik).However,the cells still have photosynthetic pigment,and they could rejuvenate to a vegetative state when re-illuminated(250 ?mol·m-2·s-1)for six days.Compare with optimal light intensity of vegetative growth,the resting stage cells could rejuvenate at a wider range of light intensities.(3)Compared with the low light intensities(250,350 ?mol·m-2·s-1),the cells of S.costatum(50,150,250,350 ?mol·m-2·s-1)in the process of rejuvenation under the higher light intensities(250,350?mol·m-2·s-1)could recover faster in growth and photosynthetic activity.The optimal light intensity for S.costatum resting stage cells rejuvenation was higher than that for vegetative cells growth.Under the higher light intensities(250,350 ?mol·m-2·s-1),they could form more vegetative cells more quickly.The optimal light intensity of rejuvenation is 350 ?mol·m-2·s-1.We concluded that under the role of the upwelling and other factors,S.costatum resting stage cells which existing in higher water layers in natural sea are capable of rapid rejuvenate,because the optimal growth water layer of vegetative cells is subsurface water where the vegetative cells growth were significantly suppressed.So the large number of red tide algae such as S.costatum in sediment could rejuvenate at higher water layers following a fast growth.These cells could take an advantage in competition with other phytoplankton and result in blooms.(4)In the early days of the recovery that the cells of S.costatum in the process of rejuvenation,there was no significance on the effects of nitrate and silicon nutrients.Phosphate nutrient may provide the material basis for the rejuvenation of the resting stage cells of S.costatum.Adequate nutrient is the important guarantee of resting stage cells during rejuvenation.