To form Microcystis blooms, Microcystis must be competitively dominant to other phytoplankton species to produce enough biomass. The aim of this study was to determine the competition mechanisms between Microcystis aeruginosa and Scenedesmus obliquus. M. aeruginosa and S. obliquus were separately cultured in the filtrate of mono and mixed cultures of M. aeruginosa and S. obliquus with varying treatments concerning N, P and iron availability. The inhibition rate for M. aeruginosa was 20–31% when cultured in mono and mixed culture filtrates enriched with N and P, but this rate was reduced to −15 to 19% when cultured in filtrates enriched with N, P and iron. The inhibition rate for M. aeruginosa decreased from 80 to 100% to 11–39% in dialytic filtrates. However, there were no differences in inhibition rate for S. obliquus, regardless of filtrate or dialytic filtrate treatments. The potential allelochemical, 2-butyl-octanol (0.144 mg L⁻¹), was found to have little inhibitory effect to M. aeruginosa or S. obliquus. Thus, previously reported allelopathy to Microcystis would be overestimated. We also report a new mechanism in phytoplankton competition in this study. The phytoplankton secreted humic acid-like substances that can reduce the bioavailability of iron, resulting in the inhibition of other phytoplankton.

为了形成微囊藻的水华，微囊藻必须在竞争性地优势于其他浮游植物，以产生足够的生物量。本研究的目的是确定铜绿微囊藻与斜栅藻的竞争机制。微囊藻和斜生栅藻在单和混合培养物的滤液中分别培养铜绿微囊藻和斜生栅藻与关于N，P和铁可用性改变治疗。铜绿假单胞菌的抑制率当在富含N和P的单培养和混合培养滤液中培养时，该比率为20-31％，但是当在富含N，P和铁的滤液中培养时，该比率降低至-15至19％。在透析滤液中，铜绿假单胞菌的抑制率从80％降至100％至11-39％。但是，不管滤液或透析滤液处理如何，斜生链球菌的抑制率均没有差异。发现潜在的化感化学物质2-丁基辛醇（0.144 mg L ^-1）对铜绿假单胞菌或斜生链球菌几乎没有抑制作用。因此，先前报道的对微囊藻的化感作用会被高估。在这项研究中，我们还报告了浮游植物竞争的新机制。浮游植物分泌的腐殖酸样物质会降低铁的生物利用度，从而抑制其他浮游植物。