Research On Quantitative Relationship Between The Growth Of Synechococcus Cf.Elongatus And Nitrogen Regeneration In The Sea

Nanoflagellates(NF)are major protozoa that prey on picoplankton and also the important contributors to the regeneration of nitrogen and phosphorus in the sea.Through ingestion and metabolism,NF could release nutrients back into the water.More and more research have shown that nano-and picoplankton as members of microbial loop,both play important roles in marine ecosystem and biogeochemical cycle due to the ocean primary productivity relying on nutrient regeneration by microbial loop living in euphotic layer.However,there are some approach limitations that people cannot fully understand the function played by plankton of different particle size.Therefore,a simple and effective method for nutrients detection in the sea area is needed,which is very important for understanding the nutrient recycling of nanoflagellates and microbial loop in the sea area.This study establishes a model organism of Synechococcus to set up a biological indicator method by exploring the relationship between the growth of Synechococcus and its initial AAN concentrations on the base of axenic treatment and optimum condition.By using this method combined with results of the voyage of the Taiwan Strait in May 2017,the regeneration and recycling of nitrogen nutrient in microbial loop of the sea area was evaluated.The main results are as follows:Use Ampicillin and Cefotaxime for purifying Synechococcus after 24 h pre-darkness treatment,and the final concentration for both is 500 mg/L.So that bacteria living in solution are greatly reduced without damaging Synechococcus cells,and the residual bacteria activity of bacteria are also inhibited.The research seeks for optimal conditions of Synechococcus growth using orthogonal experiment with three factors and three levels after purifying.It turns out that 30?,12 h:12 h light-dark cycle and 2400 lx is the optimum growth condition for both nitrate and ammonia source.Under such conditions,the intrinsic growth rate will reach at 1.238 for nitrate and 1.214 for ammonia.Use synechococcus as the biological indicator for investigating quantitative relationships between Synechococcus growth and nitrate,ammonia and urea respectively,and establish the Synechococcus indicator method concerning density increment with AAN concentration.Method detection limits for nitrate,ammonia and urea are 13 nmol N/L,11 nmol N/L and 21 nmol N/L,which have higher accuracy and lower detection limit in respect to traditional stoichiometry.Thus it provides a reliable approach for the research of the nitrogen regeneration-recycling of microbial loop in the sea.Apply Synechococcus indicator method for investigating nutrients absorption and regeneration by plankton of different particle size in the Taiwan Strait and NSCS.We find picoplankton-including heterotrophic bacteria and Synechococcus in nitrogen deficiency area,mainly absorb DIN and DIP,and release AAN.Nanoplankton mainly release DIN,DIP and AAN,while microbial loop as a whole,mainly absorb DIP and release DIN as while as AAN.As a conclusion the microbial loop has an important compensatory mechanism for the imbalance of nitrogen and phosphorus in this sea area.On the other hand,the daily supplemental rates of nitrogen by nanoflagellates feeding-extretion ammonia are 37.44%for AAN and 63.68%for DIN,respectively,which prove to be an important factor to maintain the nitrogen content and primary productivity in the sea.These above indicate it is of positive significance to study the regeneration and utilization of nitrogen nutrients by different size plankton in the microbial loop when use Synechococcus indicator method.And the assessment of ammonia excretion by nanoflagellate in Taiwan Strait fills the gap in the study area concerned,which may have reference value for understanding the function of microbial loop in this area.