营养盐比例对硅藻水华优势种小环藻生长和生理的影响

近年来，一些淡水水体如河流、水库等暴发了以小环藻为优势种的硅藻水华，对水生态系统健康产生了不利影响.为探究不同营养盐水平下营养盐结构对小环藻生长的影响作用，研究了不同N/P（N与P质量浓度之比，下同）、Si/P、Si/N下小环藻培养物的藻细胞密度、叶绿素a浓度以及叶绿素荧光参数的变化.结果表明:在试验所设定的营养盐浓度范围内，随着N/P、Si/N的升高，小环藻的藻细胞密度和叶绿素a浓度显著增加，在N/P为30、Si/N为5.0的环境中有较好的生长潜力.小环藻在磷浓度低于0.10 mg/L的水体中，生长潜能与Si/P呈正相关，最适Si/P为100；在磷浓度为0.30 mg/L条件下，最适Si/P为50.综合对比分析，水体Si/P对小环藻生长的影响最为显著.在保持水体营养盐比例不变的条件下，营养盐浓度的变化对小环藻生长亦有明显的影响.当水体氮浓度高于6.0 mg/L、磷浓度高于0.10 mg/L时，硅是小环藻的主要限制元素，其最适浓度为15 mg/L.此外，在初始磷浓度为0.03 mg/L，氮浓度低于0.6 mg/L、硅浓度低于1.5 mg/L时，小环藻生长较为缓慢，光合活性低，因此，若实际水体营养盐浓度低于此水平，将能有效控制硅藻水华的暴发.研究显示，小环藻生长最适N/P为30、Si/N为5.0；最适Si/P与初始磷浓度有关，在磷浓度低于0.10 mg/L时，最适Si/P为100；磷浓度为0.30 mg/L时，最适Si/P为50.总体而言，小环藻生长受Si/P的影响最为明显. 

Effect of Nutrient Ratios on Growth and Physiological of Cyclotella sp. of Dominant Species in Diatom Bloom

The diatom blooms that are caused mainly by Cyclotella sp. occur frequently in freshwater bodies such as rivers and reservoirs, and severely damage the aquatic ecosystems. In order to study the effect of nutrient ratios on the growth of Cyclotella sp., the changes of algal cell density, Chl-a concentration and chlorophyll fluorescence parameters in the Cyclotella sp. culture were measured under different N/P, Si/P and Si/N conditions. The results showed that with the increase of N/P and Si/N, algal cell density and chlorophyll-a concentration of Cyclotella sp. significantly increased. The growth of Cyclotella sp. could be stimulated at N/P of 30 and Si/N of 5.0. When phosphorus concentration was less than 0.10 mg/L, the growth potential of Cyclotella sp. was positively correlated with Si/P, and the optimal Si/P was 100. However, when the phosphorus concentration was 0.3 mg/L, the optimal Si/P was 50. Comprehensive comparative analysis showed that Si/P had the most significant effect on Cyclotella sp. growth. With the unchanged nutrient ratio, the variation in nutrient concentration also exhibited significant effect on Cyclotella sp. growth. When the concentration of N and P was higher than 6 mg/L and 0.10 mg/L, respectively, silicon was the major limiting factor of Cyclotella sp. growth. In addition, when the P concentration was 0.03 mg/L, and N and Si were lower than 0.6 mg/L and 1.5 mg/L, Cyclotella sp. exhibited inhibited growth and limited photosynthetic activity. Therefore, our study provides important nutrient ratio thresholds, with which the outbreak of diatom blooms can be potentially controlled. The results showed that the most suitable nutrient ratios for the growth of Cyclotella sp. were N/P of 30 and Si/N of 5.0. And the optimal Si/P was related to the initial phosphorus concentration. When the phosphorus concentration is lower than 0.10 mg/L, the optimal Si/P was 100. When the phosphorus concentration was 0.30 mg/L, the optimal Si/P was 50. In general, the growth of Cyclotella sp. was most obviously affected by Si/P.