图 7硅藻物种与环境因子的相关性 Heatmap 图和聚类树分析

Fig. 7 Correlation heatmap and clustering tree analysis between diatoms genuses and environmental factors

一致。研究表明, 适宜的水温、电导率、ph和氮磷营养盐对硅藻的生长至关重要[4,25,36]。生源物质对硅藻群落也有重要影响。大部分硅藻物种对COD有响应, 特别是Porosira和plagiogrammopsis与cod显著正相关。这是因为不同藻类利用碳元素的形式不同, 且这两类硅藻对有机碳源的需求较大[37]。总磷与大部分硅藻物种有较显著的相关性, Cyclotella和porosira与总磷显著正相关; 而部分硅藻与总磷负相关, 可能是由于硅藻可利用的磷源(如磷酸钠盐, 磷酸钾盐或磷酸钙盐等)较少。不同硅藻群落对不同形态的氮源响应也不同[34,38], Nitzschia, Surirella, Cyclotella, Porosira, Plagiogrammopsis, Skeletonema和conticribra与总氮及硝态氮均显著正相关, 因为这些硅藻主要以硝态氮为氮源; Fragilaria, Cocconeis, Gomphonema, Synedra, Planothidium和geissleria主要利用氨氮, 因此与氨氮显著正相关。已有研究表明, 在一定浓度范围内,小环藻和脆杆藻(如Cyclotella stelligera, Fragilaria pinnata var. lancettula)的丰度与no3−的浓度成正比[21]。TAN等[26]证明氮素(NH4+-N, NO3-N, TN)和COD对硅藻群落的组成影响较大。本研究发现, Cyclotella的丰度与硝态氮浓度呈正比, 而Fragilaria

丰度与硝态氮呈弱负相关, 与氨氮浓度显著正相关。基于生源物质氮和磷对硅藻群落多样性的显著影响, 本研究认为, 控制汉江中下游的水体氮磷浓度对避免硅藻水华发生有重要意义。

3 结论

采用 18S RRNA Illumina Miseq 高通量测序技术, 鉴定得到汉江中下游水样和沉积物硅藻共 4 纲28 目 49 科 111 属 160 种, 其中春季 28 目 47 科 101属 139 种, 秋季 28 目 49 科 102 属 148 种。沉积物硅藻占总物种数的 98.6%, 表明沉积物是长江生态系统硅藻物种的存储库。水体硅藻的优势种是Pinnularia, Cyclotella 和 Nitzschia, 而沉积物中的优势种是 Pinnularia, Nitzschia 和 Navicula。

汉江中下游硅藻的 Shannon 多样性指数变化范围为 2.45~4.26, 沉积物硅藻 Shannon 多样性指数比水体大。在空间分布上, 硅藻多样性存在异质性;不同季节水体硅藻多样性丰富的断面对应的沉积物硅藻多样性也丰富, 且沉积物硅藻比水体硅藻多样性丰富; 在季节影响方面, 秋季硅藻物种多样性比春季丰富。水体和沉积物硅藻的群落组成存在显著差异。水样硅藻群落组成具有较大的季节性差异, 而沉积物硅藻群落组成季节差异性小。由此表明, 生境类型是影响硅藻群落组成的重要因素。不同硅藻物种对同一环境环境因子的响应不一致。总氮、氨氮、硝态氮和总磷等营养盐对硅藻群落组成影响较大。因此, 控制汉江中下游的水体氮、磷浓度对避免硅藻水华发生有重要意义。

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