Effects of temperature,irradiance and nitrate on the growth of Cylindrospermopsis raciborskii N8

Cylindrospermopsis raciborskii N8 strain was isolated from a sub-tropical reservoir in southern China and cultured with BG-11 culture medium. The effects of temperature,irradiance and nitrate on the growth of this strain were evaluated by a designed experiment with gradients of temperature( 12,16,20,24,28,32℃),irradiance( 6. 6,12. 4,21. 5,30. 7,62. 9,106. 4 μmol/( m2·s)) and nitrate( 0. 5,1,2,4,8,16,32,64,128 mg/L). C. raciborskii N8 had normal growth at temperature between 16℃ and 32℃,and the maximum specific growth rate( 0. 189 d- 1) were observed at temperature between 24℃ and 28℃; C. raciborskii N8 could not survive at 12℃,and chlorophyll-a concentration was significantly lower than other temperature treatments( 16-32℃). C. raciborskii N8 had a wide adaptation of irradiance ranging from 6. 6 μmol /( m2·s) to 106. 4 μmol/( m2·s). An exponential growth was found from 6. 6 to 106. 4 μmol/( m2·s). The optimal irradiance was 30. 7 μmol/( m2·s) and the maximum specific growth rate was 0. 156 d- 1. C. raciborskii N8 grew faster significantly in high irradiance conditions( 62. 9-106.4 μmol/( m2·s)) than that in low irradiance conditions( 6. 6-12. 4 μmol/( m2·s)). The species began an exponential growth under nitrate of 4 mg / L,reached the highest specific growth rate( 0. 155 d- 1) at the nitrate concentration of 8 mg / L. The specifical growth rates became stable when the nitrate concentration exceeded 16 mg / L. C. raciborskii N8 grew faster significantly in the high nitrate conditions( 16-128 mg / L) than that in the low nitrate conditions( 0. 5-2 mg / L). The present ex-periments demonstrated that C. raciborskii N8 can adapt for wide temperatures,irradiance and nitrates,and has a potential to colonize and distribute in divers water body over a large scale.