The Response To Nitrogen Nutrient, And The Uptake Kinetics Mechanism Of Nitrogen And Ecophysiological Analysis Of Enteromorpha Prolifera

In late June 2008, the waters and shores of the Olympic sailing events'Qingdao venue on China's north-eastern coast experienced a massive green-tide covering 400 km2. The green-tide lasted over two weeks and the resultant cleanup involved more than 10,000 people and removed over one million tonnes of algae from the beach and coast of Qingdao. The green-tide was comprised of Enteromorpha prolifera which has been previously reported as one of the dominant benthic algae in the littoral zone of China.The original source of this seaweed was suspected to be from the south of the Yellow Sea as revealed bysatellite images.The floating biomass drifted with water current northward and flourished in nearshore waters around Qingdao. The initial causes were attributed to coastal eutrophication and suitable conditions in Qingdao coasts by some scientists. The vegetative growth habit of the species and spore dispersal in the water helped to enlarge biomass in the water during the outbreak stage of green tide. Our investigation looked for the response to nitrogen nutrient, and the uptake kinetics mechanism of nitrogen and ecophysiological analysis of Enteromorpha prolifera. This will provide information about the link between E. prolifera blooms and nitrogen nutrient enrichment. The details were as follows:1. Several kinds of inorganic nitrogen, organic nitrogen, and their mixtures were selected as nitrogen sources. The growth of E. prolifera was affected by different N sources, N concentrations, and culture methods. Our results show that NH₄⁺ and NO₃^- were utilized effectively by E. prolifera, and that NO₂^- and urea at a range of several to dozens ofμmol L?1 were also effectively utilized. When supplied with another nitrogen source, NH₄⁺ was preferentially assimilated by E. prolifera. A single, high-concentration addition of the N source was favorable for rapid growth of E. prolifera, whereas intermittent addition of the N source was favorable for prolonged growth.2. By selecting different physical and chemical factors, the orthogonal design was used to investigate their impacts on absorption kinetics and ecophysiological indicators of E. prolifera, and access the relevant parameters of nutrient uptake kinetics for judging the ecological habits and physiological characteristics of E. Prolifera. Under the same conditions, NH₄⁺ was preferentially absorbed by E. Prolifera, and the absorption rate of NH₄⁺ was greater than that of NO₃^-. The nitrogen assimilation in vivo of E. prolifera was constrainted by its absorption firstly, while the accumulated NO₃^- concentration in vivo can adjust the absorption and assimilation of NO₃^-. Moreover, nitrate reductase activity (NRA) can not be used to indicate the absorption rate of NO₃^-, but glutamine synthetase activity (GS) can be used to reflect the absorption rate of NH₄⁺.3. NO₃^- and NH₄⁺ which are the most common N sources in seawater, and readily assimilated by E. Prolifera were selected as nitrogen sources to study the interaction between their absorption kinetics. The results show that E. Prolifera can take advantage of NO₃^-and NH₄⁺ with higher concentrations in seawater respectively, and NO₃^-and NH₄⁺ would inhibit the absorption of each other, but the inhibition action of NO₃^- on NH₄⁺ was weaker..4. For the increasingly serious and complex pollution status, the study about the impact of single nutrients or heavy metals on marine phytoplankton growth has been far from solving practical problems, it needs to consider many factors comprehensively. Pb(II), Cu(II), Cd(II), Zn(II) and Fe(III) were selected to research their impacts on nitrogen uptake kinetics and ecophysiological indicators of E. Prolifera. The results show that these heavy metals selected can significantly affect NRA, the accumulated NO₃^- concentration in vivo, the induced NO₃^- concentration in vivo and GS of E. Prolifera, which thus affect the absorption rate of NH₄⁺ and NO₃^-.