氮磷比对固氮和非固氮蓝藻种间关系的影响

Influence from nitrogen-phosphorusration ratio on interspecific relationship between N-fixing and non N-fixing cyanobacterias

蓝藻是引起水华暴发的主要藻类之一,氮磷比N∶P是影响水体中固氮蓝藻形成的重要参数。然而在水体不同富营养化程度下,N∶P对固氮和非固氮蓝藻的种间关系影响仍不清晰。通过构建氮磷摩尔比为2、16和64的培养体系,比较固氮蓝藻的水华鱼腥藻(Anabaena flos-aquae)和非固氮蓝藻惠氏微囊藻(Microcystis wesenbergii)在单培养和混合培养条件下的增长速率、最大环境容纳量和竞争系数,研究不同N∶P环境中固氮和非固氮蓝藻功能群的种间关系。结果表明:在三种N∶P条件下,纯培养和混合培养的微囊藻的生长速率和最大环境容纳量均高于鱼腥藻。纯培养中微囊藻在N∶P=16条件下细胞密度可达最大,为818×10~4cells/m L,而纯培养中鱼腥藻在N∶P=2条件下细胞密度最大,为113×10~4cells/m L。在不同N∶P条件下微囊藻在混合培养体系中的最大密度均高于纯培养体系,而鱼腥藻的生长趋势正好相反。这说明固氮和非固氮蓝藻在不同N∶P条件下均呈现偏利于非固氮蓝藻的种间关系。水华鱼腥藻的竞争能力较弱,但在其与微囊藻的混合培养体系中为微囊藻提供新氮,从而促进非固氮蓝藻微囊藻增殖。

Cyanobacteria is one of the main algal group to cause algal blooms. The nitrogen to phosphorus ratio （N： P） is a major factor that affecting the N-fixing cyanobacteria proliferation. However, the N ： P ratio influencing on the interspecific rela- tionships between N-fixing and non-N-fixing cyanobacteriais still unclear. Through establishing the pure-and mixed-cultures with the N： P molar ratio of 2, 16 and 64, the growth rates, capacity and competition coefficients of Anabaenaflos-aquae （N- fixing cyanobacteria） and Microcystis wesenbergii （non-N-fixing cyanobacteria） were determined. Furthermore, the inter- specific relationships between the A. flos-aquae and M. wesenbergiiin under N ： P were studied. The result showed that the growth rate and maximum environmental carrying capacity of M. wesenbergli were higher than those of A. flos-aquae in both pure-and mixed-cultures. The cell density of M. wesenbergii in pure-cuhuresreached the maximum （818 × 10^4 cells mL^-1） under N： P = 16, and the cell density of A. flos-aquae inpure culturedreached the maximum （113×10^4 cellsmL-1 ） under N ： P = 2. Moreover, the maximum cell densities of M. wesenbergii in mixed-cultureswere higher than those in pure-cultures under all N ： P conditions, but the A.flos-aquae showed an opposite trend of those. The results suggested that it was more beneficial to non-N-fixing M. wesenbergii under all N ： P conditions in mixed-cultures. Although the competitive ability of A. flos-aquae was weaker, it can provide new nitrogen for M. wesenbergii in mixed-cuhures, and thuspromote the proliferation of non-N-fixing M. wesenbergii.