Abstract:

The long-term ecological control of harmful cyanobacteria, such as Microcystis, in eutrophic water is related to the response and impacts of the microecosystem where they occur. Periphytic algae, which share the same ecological niche as submerged macrophytes, may play an important role in the stabilization of freshwater ecosystems. There have been many studies on the inhibitory effects of submerged plants on cyanobacteria, such as Microcystis, but how periphytic algae respond to and affect this process is still unclear. In this study, three common submerged Hydrocharitaceae plants, Vallisneria natans, Hydrilla verticillata, and Elodea nuttallii, were selected to co-culture with each of the two Microcystis strains respectively under controlled indoor conditions for 18 days. The growth responses of each Microcystis strain and plant species were measured, and the response of the periphytic algae community was monitored. The results showed that the three submerged plants with an initial fresh weight of 2.0 g∙L⁻¹ had significant inhibitory effects on two strains of Microcystis with an initial density of (3.5±0.1×10⁶) cells∙mL⁻¹. On Day 6, the inhibitory rates exceeded 80%. The inhibitory effect of E. nuttallii on Microcystis was the strongest among the three plants. However, the growth of the three plants was also affected by Microcystis to varying degrees. Some leaves of V. natans began to decay and decompose from Day 6, while the fresh weight and plant length of E. nuttallii and H. verticillata did not significantly increase compared to Day 0 in the co-cultured treatments. With the inhibition of Microcystis by the three plants, ammonium concentrations in the water gradually increased, peaking around Day 9 to Day 12, followed by a decrease. Periphytic algae began to appear on the bottom and inner walls of the beakers in all treatments from Day 9. At the end of the experiment, the density of periphytic algae in the plant-Microcystis co-cultured treatment was higher, but the diversity was lower, compared to the plant monoculture control. The relative cell density of periphytic cyanobacteria in the co-cultured treatment of Microcystis with E. nuttallii and H. verticillata was significantly higher than that in the plant monoculture control, whereas the relative density of filamentous cyanobacteria, such as Limnothrix sp. and Leptolyngbya sp., in the co-cultured treatment of Microcystis with V. nantas and H. verticillata was higher compared to the plant monoculture control. These findings indicate that periphytic algae may help regulate nutrient levels in the water column, and work alongside submerged plants to maintain a clear-water state by absorbing and utilizing the nutrients released from the death and decomposition of Microcystis. However, the dominance of periphytic filamentous cyanobacteria poses potential ecological risks, requiring strengthened monitoring, prevention, and control measures.

Key words: Vallisneria natans, Hydrilla verticillate, Elodea nuttallii, submerged plant, Microcystis, periphytic algae, filamentous cyanobacteria

摘要：

富营养水体微囊藻（Microcystis）等有害蓝藻生态防控的长效性与所处微生态系统的响应和影响有关，其中周丛藻类与沉水植物处于同一生态位，在淡水生态系统稳态转换方面具有重要作用。沉水植物对微囊藻等蓝藻的抑制作用研究较多，但周丛藻类如何响应和影响这一过程还不清楚。为此，选择3种常见水鳖科沉水植物苦草（Vallisneria natans）、轮叶黑藻（Hydrilla verticillata）、伊乐藻（Elodea nuttallii）健康植株与2株微囊藻（Microcystis sp.），在室内可控条件下分别共培养18 d，测定每株微囊藻和每种植物生长变化的同时，观察各实验组周丛藻类群落结构的响应。结果表明，鲜质量为2.0 g∙L⁻¹的3种沉水植物对起始密度为 (3.5±0.1)×10⁶ cells∙mL⁻¹的2株微囊藻抑制作用显著，第6天，抑制率均超过80%，伊乐藻的抑藻效果最强。但3种植物也受到微囊藻不同程度的影响，苦草部分叶片从第6天开始死亡分解，伊乐藻和轮叶黑藻鲜质量和株长未明显增加。伴随着3种植物对微囊藻的有效抑制，水环境中氨氮浓度不断增加，在第9－12天达到峰值后再逐渐降低。从第9天开始，各实验组烧杯底部和内壁开始出现附着藻类。实验结束时，相比于植物单培对照组，植物与微囊藻共培组中周丛藻类密度更高，多样性更低。伊乐藻、轮叶黑藻与微囊藻共培组周丛蓝藻相对密度明显高于植物单培组，而苦草、轮叶黑藻与微囊藻共培组丝状蓝藻泽丝藻（Limnothrix sp.）、细鞘丝藻（Leptolyngbya sp.）相对密度高于植物单培组。由此推测，周丛藻类可吸收利用微囊藻死亡分解后释放的营养物质，降低水体营养水平，与沉水植物协同维持清水稳态，但周丛藻类中优势度较高的丝状蓝藻存在潜在生态风险，应加强监测与防控。

关键词: 苦草, 轮叶黑藻, 伊乐藻, 沉水植物, 微囊藻, 周丛藻类, 丝状蓝藻