The Ecophysiological Responses Of Harmful Algal Chattonella Marina To Nitrogen And Phosphorus

The blooms of Chattonella marina which caused mass mortalities of fishes or invertebrates, resulted in serious damage to aquaculture industries.The growth characteristics and ecophysiological responses of C.marina to nutrients(in particular nitrogen and phosphorus) were carded out using lab-based incubation experiments.The strategies of C.marina to the variations of environmental nutrients were emphasized on,and C.marina advantaged in competing for nutrients and its mechanisms were discussed.The main results were as follows: (1) C marina is a nutrients-dependent species and the algae multiplied exponentially after adding nitrate or phosphate into the culture.The growth of C.marina was significantly restricted by nutrient,especially by P limitation.The cells of C.marina could hardly grow in the media without Nand P addition.The optimum N:P ratio of C.marina was 8/1,and the cells grew better in lower N:P ratio.(2) In supplemented the same nitrogen or phosphorus sources separately,Chattonella marina cells showed significant growth in the number,the growth rate has markedly improved.(3) Chattonella marina can utilize several different kinds of DON such as urea,glycin,and 1,4-diaminobutane hydrochloride,but threonine could not be utilized,The maximum growth rate was 0.7 d^-1.The results also indicated that C.marina could utilize glucose-6-phosphate(G-6-P), sodium glycerophosphate(G-P) and adenosine triphosphate(ATP) as phosphorus sources,but lecithin could not be utilized,the maximum growth rate was 0.56 d^-1.(4) The results of short-term uptake experiments showed that the maximum uptake rate(ρ_max) and half saturation constant(K_s) of C.marina were 0.17 pmol cell^-1 h^-1 and 1.08μM for phosphate;1.42 pmol cell^-1 h^-1 and 3.46μM for ammonium;and 1.13 pmol cell^-1 h^-1 and 6.89μM for nitrate,respectively.The specific maximum growth rate(μ_max) and the minimum cell quota (Q₀) obtained from the semi-continuous growth experiments,were 1.09 day^-1and 0.22 pmol cell^-1 for P-limited conditions,and 1.2 day^-1 and 2.98 pmol cell^-1 for the N-limited conditions.It can be presumed that C.marina,with the higher growth rate and rich nutrient storage ability in natural marina water,is likely to form blooms when external abundant pulse nutrients were imported.(5) Nitrate reductase activity(NRA) and alkaline phosphatase activity(APA) of C.marina were investigated under different nitrogen sources or phosphorus conditions.The results indicated that the NRA_max of C.marina was 20.6 fmol/(min·cell) when NO₃-N was added as the nitrogen source,whereas the expression of nitrate reductase activity were significantly limited by urea, glycin and 1,4-diaminobutane hydrochloride.Different species of phosphorus had different effect on APA,The expression of alkaline phosphatase activity were significantly limited by G-6-P,ATP and G-P.The maximum hydrolyzing rate(â…¤_max) and half saturation constant(K_s) of C.marina were 8.17 pmol cell^-1 h^-1 and 15.1μM for phosphate,and no high affinity AP system for hydrolyzing SNP was found.