Uptake And Utilization Characteristics Of Prorocentrum Donghaiense For Urea

The temporal and spatial distribution of urea concentration and the composition of phytoplankton community were investigated all the year round in aquaculture areas of Daya Bay. Meanwhile, the growth and uptake dynamics of a representative harmful algal bloom species Prorocentrum donghaiense for urea were studied in laboratory. And effects of light, temperature, salinity, and nitrogen sources for the growth and urease activity of P. donghaiense were discussed for further understanding the uptake and utilization mechanisms of marine microalgae for urea and revealing effect of the increase of urea concentration for community succession of phytoplankton and its potential contribution to the formation of HABs in coastal waters. The main results were as follows:The average concentration of urea was 28.2μgN/L in aquaculture areas of Daya Bay, which represented about 20% of DON. The highest concentration of urea appeared in autumn, significantly higher than the other three seasons. Temperature was an important factor controlling the composition of phytoplankton community. Under suitable temperature circumstances, higher concentration of urea was also conducive to the growth of dinoflagellates. Diatom possessed advantage throughout the year. The dominant species were Rhizosolenia alata and Chaetoceros spp.. In April, May and November, Dinoflagellates density increased significantly. The dominant species were Prorocentrum spp., Alexandrium spp., Scrippsiella trochoidea, Chattonella marina, Karenia mikimotoi, Akashiwo sanguine, Dinophysis acuminate, et al.The specific growth rates of P. donghaiense with nitrogen gradients could be described by a rectangular hyperbola, similar to the Michaelis-Menten equation for enzyme kinetics. The maximum specific growth rate of P. donghaiense as a function of urea concentration was 0.685d-1 and the half-saturation concentration was 20.508μmolN/L. The maximum specific growth rates of P. donghaiense as a function of nitrate concentration was 0.663d-1 and the half-saturation concentration was 11.940μmolN/L. The half-saturation concentration of P. donghaiense under nitrate was lower than that under urea. So the affinity of P. donghaiense for nitrate was higher than urea. However, when nitrogen sources were sufficient, P. donghaiense grew faster in urea.Response of P. donghaiense to urea and ammonia were very fast but decayed rapidly with time. The maximum absorption rate and half saturation constant of P. donghaiense in ammonium chloride were 2.800 h"1 and 18.032μmolN/L. The maximum absorption rate and half saturation constant of P. donghaiense in urea were 3.184h-1 and 39.043μmoIN/L. The maximum absorption rates and half saturation constants of P. donghaiense for ammonia and urea were all in the same order of magnitude.Inactivation time, pH value of the extract, incubation temperature and growth phase of microalgae all significantly influenced urease activity in microalgae. Light, temperature, salinity and other environmental factors not only influenced the growth and urease activity of P. donghaiense, but also changed the carbon and nitrogen composition of the cell. Nitrogen source was an important factor regulating urease activity of P. donghaiense:urea showed positive effect, whereas ammonia had negative effect.