Application Of Chlorophyll Fuorescence In Detecting Phytoplankton Nutrient Limitation And Following Red Tide

Nutrients are of great importance for phytoplankton growth and the concentrationof nutrients in the seawater is changing with seasons and sea areas. As the differencein the ability to store nutrients for phytoplankton and/or their potential to use storednutrients for growth, research basing on nutrient is always the difficult and hot spotfor marine scientists. Chlorophyll fuorescence is being used as a new technique indetecting nutrient limitation for the advantage of sensitive, fast and convenient.However, studies have shown that changes in chlorophyll fuorescence are differentamong algae species and with the limited nutrient. In this paper, the application ofchlorophyll fuorescence was studied in the labrary and in situ. The main researchwork and conclusions are listed as follows:1The effects of different nutrient supply on the maximal quantum yield ofphotosystem Ⅱ (F_v/F_m) to seven algae in nitrate-starved and phosphorus-starvedbatch cultures were monitored in order to find weather it could be used to determineN and P limitation in the seven algae. The results showed that F_v/F_mis sensitive to N,P limitation in Chaetoceros debilis, Coscinodiscus sp., Dicrateria inornata,Platymonas subcordiformis and Heterosigma akashiwo while it is not sensitive inSrippsiellla trochoidea and Prorocentrum donghaiense. The results suggested thatF_v/F_mwas not a robust diagnostic for nutrient limitation in dinoflagellates.2The effects of different nutrient supply on F_v/F_mto Gymnodinium andChaetoceros gracilis in N-starved and P-starved semi-continuous cultures weremonitored in order to find weather F_v/F_mcould be used to determine N and Plimitation of the two algae in semi-continuous cultures. The results showed that it isnot a robust indicator of N, P limitation in semi-continuous cultures.3The effects of different nutrient supply on F_v/F_mto five algae in N-starved andP-starved batch cultures under15℃，20℃and25℃were monitored in order to assessthe effects of temperature on F_v/F_m. The results showed that the sensitivity of F_v/F_mtonutrient limitation is largely depended on the species of the algae. The temperature has little effects on F_v/F_munless it is beyond the endurance of algae. So when usingthis method in detecting nutrient limitation in situ, the effects of temperature can beneglected.4The F_v/F_mdistribution of Qingdao coast and the East China Sea was investigatedin this research. The results showed that the F_v/F_mdistribution has good correlationswith chlorophyll and nutrients. The value of F_v/F_mcan be used to reflect nutrientstatus.5The effects of different nutrient supply on F_v/F_mto the seawater of fourinvestigation stations were monitored in order to detect the nutrient status. The resultsshowed the growth of phytoplankton in No.2station of Qingdao coast is limited by Pwhile that of No.6station is limited by N, P and Si. Phytoplankton in DH2-3andDH6-2stations of the East China Sea were both limited by N. Basing on thechanges of F_v/F_m, it can be inferred which nutrient can result in the explosion of algae.Control the influx of the limited nutrient can help to prevent the broke out of red tides.6Mesocosm experiments were conducted in the East China Sea to simulate thedevelopment of red tide. The results showed that the dominant red tide specie changedfrom diatom to dinoflagellate accompanied with the changes of F_v/F_m. As a result,F_v/F_mcan be used to follow the development of red tide. It is a convenient, promptand precise method in following the development of red tides.