Size-Dependent Growth Rate of Nitzschia closterium at Different Concentrations of Petroleum Hydrocarbon

The maximum growth rate of Nitzschia closterium at various concentrations of petroleum hydrocarbon was studied. The influence of petroleum hydrocarbon on cell size as a function of concentration was discussed. The relationship between maximum growth rate of Nitzschia closterium and cell median equivalent spherical diameter (MESD) was also carefully studied. The experimental results showed that the growth rate of Nitzschia closterium was generally suppressed by petroleum hydrocarbon, which had greater effects at both low and high concentrations than at intermediate concentrations. No significant changes in cell size distribution were observed during the growth period of Nitzschia closterium. The Gaussian function could give a clear description of the cell size distribution of Nitzschia closterium, and the MESD value ranged from 2.71 to 6.82 μm. The MESD decreased when the cell was exposed to petroleum hydrocarbon, and the reduction of cell MESD was much more significant at both relatively high and low hydrocarbon concentrations. The presence of petroleum hydrocarbon changed the relationship between μmax and MESD from an allometric function to a U-shaped curve. When the MESD was below 5.07 μm, μmax decreased along with increased MESD, whereas when MESD was above 5.07 μm, μmax increased along with MESD, which deviated from the allometric model.

The maximum growth rate ofNitzschia elosterium at various concentrations of petroleum hydrocarbon was studied. The influence of petroleum hydrocarbon on cell size as a function of concentration was discussed. The relationship between maximum growth rate of Nitzschia closterium and cell median equivalent spherical diameter （MESD） was also carefully studied. The experi- mental results showed that the growth rate of Nitzschia elosterium was generally suppressed by petroleum hydrocarbon, which had greater effects at both low and high concentrations than at intermediate concentrations. No significant changes in cell size distribu- tion were observed during the growth period ofNitzsehia closterium. The Gaussian function could give a clear description of the cell size distribution ofNitzsehia closterium, and the MESD value ranged from 2.71 to 6.82 μm. The MESD decreased when the cell was exposed to petroleum hydrocarbon, and the reduction of cell MESD was much more significant at both relatively high and low hydrocarbon concentrations. The presence of petroleum hydrocarbon changed the relationship between μmax, and MESD from an allometric function to a U-shaped curve. When the MESD was below 5.07 μm,μmax decreased along with increased MESD, whereas when MESD was above 5.07 μm, μmax increased along with MESD, which deviated from the allometric model.