不同初始氮浓度下尖状栅藻同化硝态氮和CO2的研究

尖状栅藻（Scenedesmus acuminatus（Lagerheim） Chodat）是一种高产油淡水单细胞绿藻，该藻在较低氮素浓度下能显著提高产油效率，是生产生物柴油的理想藻株。本研究以尖状栅藻为实验材料，通过测定藻细胞硝酸还原酶和Rubisco活性、碳氮元素含量和培养液硝酸根离子浓度，分析18.0、9.0、6.0、3.6 mmol·L^-1初始氮浓度下尖状栅藻的碳氮同化特征和时相变化规律。结果显示，18.0 mmol·L^-1组尖状栅藻细胞密度最高，为7.9×10⁷ cells·mL^-1，硝酸还原酶和Rubisco的活性高，且持续时间长。培养液中产生的NO₂^-随初始氮浓度的升高而增多，18.0 mmol·L^-1组至培养期结束仍保持相对较高的NO₂^-水平。4个实验组（初始氮从高到低）培养10 d藻细胞的氮含量依次为7.2%、4.1%、2.8%和1.9% DW，碳含量为46%、52%、54.5%和57.4% DW，细胞的C/N摩尔比值为：8.0、16.7、24.3和35.2。研究结果表明初始氮浓度影响尖状栅藻的生长繁殖，藻细胞的碳氮同化相互影响，适宜的低氮浓度可促进藻细胞碳固定。

Assimilation of nitrate-nitrogen and carbon dioxide by Scenedesmus acuminatus under different initial nitrogen concentrations

Scenedesmus acuminatus is a unicellular freshwater green microalga that can accumulate high lipid content.Lower nitrogen concentrations can evidently increase lipid accumulation in S.acuminatus,which makes it a promising source for biodiesel production.In this study,the characteristics and phase changes of carbon and nitrogen assimilation of S.acuminatus were studied under different initial nitrogen concentrations (18.0,9.0,6.0,and 3.6 mmol·L^-1) by measuring the activities of nitrate reductase and Rubisco,the intracellular C and N contents,and the NO₃^- concentration in media.Results showed that S.acuminatus achieved the highest cell density,7.9×10⁷ cells·mL^-1 in the 18.0 mmol·L^-1 group.The cellular nitrate reductase and Rubisco activities were also the highest and lasted longest in this group.With the increase of initial nitrogen concentration,the production of NO₂^- increased in the medium,whereas the 18.0 mmol·L^-1 group maintained a relatively high NO₂^- level at the end of the culture period.After 10 d of cultivation,the nitrogen contents in the four experimental groups (from 18.0 to 3.6) were 7.2%,4.1%,2.8%,and 1.9%,respectively,the carbon contents were 46%,52%,54.5%,and 57.4%,respectively,and the molar C/N ratios were 8.0,16.7,24.3,and 35.2,respectively.In conclusion,initial nitrogen concentration had significant impact on the growth of S.acuminatus.Furthermore,the carbon and nitrogen assimilations of the algae interacted with each other,and the fixation of carbon in S.acuminatus was promoted under low nitrogen concentrations.