Effects Of Nutrient On The Community Succession Of Six Marine Microalgae

The community succession and interspecific relationship of marine microalgae is animportant part of marine ecosystems. The community succession is a very complex process,affected by various environmental facts. The community succession and interspecific relationship,with red tide arises frequent, becomes a hot research in recent years, which is relation to anexplanation of outbreak and control for red tide. As terms for the growth of microalgae, thenutrients are important facts affecting the succession of microalgae. Under controlled conditionsand nitrogen, phosphorus and iron as core nutrients in laboratory, the effects of nutrient levels,nutrient forms and modes of nutrient input on the community succession of marine microalgae arestudied, using3-6kinds of common marine phytoplankton. The main results are outlined asfollows:1. Under different nutrient concentrations （f, f/2, f/4, f/8）, different N concentrations（149.6mg/l、74.8mg/l、37.4mg/l、18.7mg/l）, different P concentrations （8.8mg/l、4.4mg/l、2.2mg/l、1.1mg/l） and different Fe concentrations （7.8mg/l、3.9mg/l、1.95mg/l、0.98mg/l）, Phaeodactylumtricornutum, Dunaliella salina and Karenia mikinotoi are cultured for monoculture and mixedculture. Compared to monoculture, the growth of three microalgae in mixed culture is suppressedunder different nutrient concentrations and different N, P, Fe concentrations. In different nutrientconcentrations, P. tricornutum is dominant and accounts for more than60%of the total celldensity. With the decline of nutrient concentrations, the proportion of D. salina descends, withrise for K. mikinotoi. K. mikinotoi has competitive advantage in low nutrient concentration. Indifferent N concentrations, P. tricornutum is dominant and accounts for more than70%of thetotal cell density. The optimal N concentration for the growth of D. salina is74.8mg/l, in which D.salina has the largest proportion of the total cell density and has a competitive advantage. Withthe decline of N concentrations, the competitiveness of K. mikinotoi increases. In high Pconcentration （8.8mg/l）, P. tricornutum has the absolute competitive advantage and accounts formore than70%of the total cell density. For the other three P concentrations, the proportion oftotal cell density of D. salina and K. mikinotoi increases. With the decline of P concentrations, thecompetitiveness of K. mikinotoi increases. In low Fe concentration （0.98mg/l）, D. salina has the competitive advantage and accounts for more than50%of the total cell density. For the otherthree Fe concentrations, P. tricornutum is dominant. The change of Fe concentrations has littleeffect on K. mikinotoi.2. Under different nitrogen sources （NaNO₃, urea, NH₄Cl） and different phosphorus sources（NaH2PO4, glycerophosphate, adenosine triphosphate disodium）, P. tricornutum, D. salina and K.mikinotoi are cultured for monoculture and mixed culture. As NaNO₃and urea are nitrogen source,P. tricornutum is dominant and accounts for more than60%of the total cell density. While NH₄Clis the nitrogen, D. salina becomes the competitive species, because of the low availability ofNH₄Cl for K. mikinotoi. K. mikinoto has relatively large proportion of the total cell density whenNaNO₃and urea are nitrogen sources. P. tricornutum has a better use of organic phosphorus,glycerophosphate and adenosine triphosphate disodium, than inorganic phosphorus sourceNaH₂PO₄, and accounts for more than50%of the total cell density in the two organic phosphorus.When NaH2PO4is phosphorus source, the proportion of D. salina and K. mikinoto in the total celldensity is larger than the two other treatments.3. Under different modes of nutrient input （input one time, input every2days, input every5days）, P. tricornutum, D. salina and K. mikinotoi are cultured for monoculture and mixed culture.The high frequency of nutrient input is favor of P. tricornutum. With the acceleration of the inputfrequency, the proportion of P. tricornutum increases. P. tricornutum accounts for more than90%in nutrient input every2days, while D. salina and K. mikinotoi could account a relatively largeproportion only in nutrient input one time.4. Because microalgae is various in nature, the more microalgae for mixed culture, the closerto nature condition. Under different nutrient concentrations （2f, f/2, f/8）, different Nconcentrations （299.2mg/l,74.8mg/l,18.7mg/l）, different P concentrations （17.6mg/l,4.4mg/l,1.1mg/l）, different Fe concentrations （15.6mg/l,3.9mg/l,0.98mg/l）, different nitrogen sources（NaNO₃, urea, NH₄Cl）and different phosphorous sources （NaH2PO4, glycerophosphate, adenosinetriphosphate disodium） and different modes of nutrient input （input one time, input every2days,input every5days）, P. tricornutum, Nitzschia closterium f.minutissima, D. salina, Platymonashelgolandica var. tsingtaoensi, K. mikinotoi, Amphidinium carterae Hulburt are mixed cultured inthe experiments. Chlorophyta is dominant in high nutrient concentration （2f）, and accounts for74%of the total cell density. The competition of diatom rises with the nutrient concentrationdecrease. Diatom dominates at f/8and accounts for55%of the total cell density. Diatom dominates in high N concentration （299.2mg/l）, and accounts for56%of the total cell density.The competitiveness of diatom declines with the N concentration decreases. When Nconcentration is18.7mg/l, the proportion of diatom and chlorophyta is48%and46%respectively.Chlorophyta is the dominant species in high P concentration （17.6mg/l）, and accounts for63%ofthe total cell density, while diatom becomes dominant with the P concentration declines. When Pconcentration is1.1mg/l, diatom accounts for54%of the total cell density. Diatom has acompetitive advantage in high Fe concentration （15.6mg/l） and low Fe concentration （0.98mg/l）,and accounts for71%and52%of the total cell density respectively. As NaNO3and NH₄Cl arenitrogen sources, diatom is the dominant algae and accounts for58%and56%of the total celldensity respectively. Chlorophyta has some competitive advantage when urea is nitrogen sourceand accounts for56%of the total cell density. When NaH₂PO₄and glycerophosphate arephosphorus sources，diatom is the competitive species, and accounts for58%and59%of the totalcell density respectively. Chlorophyta is the dominator in adenosine triphosphate disodium asphosphorus source, and accounts for80%of the total cell density. For different modes of nutrientinput, the competition of diatom decreases with the weakening of the input frequency, but acertain advantage. The cell proportion of diatom achieves85%in nutrient input every2days. Thepulse input of nutrient is good for the diatom becoming the dominant species. Dinoflagellate isinhibited and only occupies small percentage of the total cell density in all the treatments.