Effect of Initial Phosphorus Concentration on Chlorophyll a Contents and Extracellular Polysaccharides Contents of Scenedesmus quaclricauda in TGR

Abstract

An experiment was carried out to evaluate the effects of initial phosphorus concentration (0, 0.54, 2.7, 5.4, 10.8and 16.2mg/L) on chlorophyll a (chl-a) contents and extracellular polysaccharides (EPS) contents of Scenedesmus quaclricauda, which was separated and purified from the Three Gorges reservoir (TGR). The different conditions of initial phosphorus concentration have different volumetric meanings. 0mg/L, 0.54mg/L and 2.7mg/L are P-limited, 5.4mg/L is P-standard, 10.8mg/L as well as 16.2mg/L, is P-rich. Results showed that the growth period of Scenedesmus quaclricauda was shortened, and the stationary phase happened earlier than usual in the condition of P-limited. However, the growth period of Scenedesmus quaclricauda got a proceeding extension in the condition of P-rich. The condition of P-rich had an inhibitory effect on the growth of Scenedesmus quaclricauda during lag phase and exponential phase. It seemed that there was an inhibition threshold of initial phosphorus concentration, which was between 5.4mg/L and 10.8mg/L. And the inhibitory effect decreased with the initial increasing phosphorus concentrations from 10.8mg/L to 16.2mg/L. One-way analysis of variance (ANOVA) was used to compare the effects of both P-limited and P-rich and their impact on sEPS contents and bEPS contents of Scenedesmus quaclricauda in the cultured time segments. The results showed that there was no significant difference at sEPS contents or bEPS contents either in P-limited or P-rich. In the whole culture period, the sEPS contents of Scenedesmus quaclricauda had small fluctuations but kept nearly unchanged. Whereas, the bEPS contents increased in the beginning 8 days, and then dropped to the level, which is slightly higher than the initial contents, and keep fluctuating steadily. The EPS contents were just floating up and down at the initial value and had not shown a trend of rising or falling precisely. Our results suggest that phosphorus concentration could change chl-a contents but have no significant effect on EPS contents.