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<p>The role of nutrients and temperature in competition-driven allelopathic interactions between macrophytes and cyanobacteria is overlooked in assessing the potential of macrophytes to control harmful cyanobacterial blooms. This study aimed to evaluate the inhibitory effects of the submerged macrophyte <i>Egeria densa</i>— in its physical presence and through its extracts—on the growth and saxitoxin (SXT) production of the cyanobacterium <i>Raphidiopsis raciborskii</i> under varying temperatures (24°C, 28°C, and 32°C) and enriched levels of phosphorus and nitrogen. The results demonstrated that the inhibitory effects of <i>E. densa</i> on <i>R. raciborskii</i> were influenced by the type of macrophyte exposure, temperature, and nutrient concentration. The physical presence of <i>E. densa</i> generally exerted a greater suppressive effect on the cyanobacterium than its extracts; however, increasing temperatures and nutrient levels favored cyanobacterial growth, reducing the macrophyte's inhibitory power, especially at 28°C. Notably, the inhibitory effect of the extracts was more pronounced at 32°C, regardless of nutrient concentration. Saxitoxin concentrations were generally positively correlated with <i>R. raciborskii</i> biomass but decreased when the cyanobacterium was exposed to the macrophyte. During exposure to the physical presence of <i>E. densa</i> at 24°C and to its extracts at 32°C, toxin levels were negatively related to biomass, suggesting a possible physiological response to stress induced by the macrophyte or toxin release due to cell death and lysis. These findings indicate that temperature and nutrients complicate allelopathic interactions between macrophytes and cyanobacteria, and that <i>E. densa</i> extracts hold promise for controlling toxic blooms of <i>R. raciborskii</i> in a warmer and more eutrophic future.</p>

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Influence of temperature and nutrients on the inhibitory effects of the submerged macrophyte Egeria densa on the growth and saxitoxin production of the cyanobacterium Raphidiopsis raciborskii

  • 期刊论文

  • 发表日期：

    2025年3月12日

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  • Jefferson Vitor Melo Cabral,
  • Juliana dos Santos Severiano,
  • Ranielle Daiana dos Santos-Silva,
  • Aline Maria Bezerra Nery,
  • Mateus Santos de Araújo-Silva,
  • Regina Anya Otogo,
  • Mathias Ahii Chia,
  • José Etham de Lucena Barbosa

摘要

The role of nutrients and temperature in competition-driven allelopathic interactions between macrophytes and cyanobacteria is overlooked in assessing the potential of macrophytes to control harmful cyanobacterial blooms. This study aimed to evaluate the inhibitory effects of the submerged macrophyte Egeria densa— in its physical presence and through its extracts—on the growth and saxitoxin (SXT) production of the cyanobacterium Raphidiopsis raciborskii under varying temperatures (24°C, 28°C, and 32°C) and enriched levels of phosphorus and nitrogen. The results demonstrated that the inhibitory effects of E. densa on R. raciborskii were influenced by the type of macrophyte exposure, temperature, and nutrient concentration. The physical presence of E. densa generally exerted a greater suppressive effect on the cyanobacterium than its extracts; however, increasing temperatures and nutrient levels favored cyanobacterial growth, reducing the macrophyte's inhibitory power, especially at 28°C. Notably, the inhibitory effect of the extracts was more pronounced at 32°C, regardless of nutrient concentration. Saxitoxin concentrations were generally positively correlated with R. raciborskii biomass but decreased when the cyanobacterium was exposed to the macrophyte. During exposure to the physical presence of E. densa at 24°C and to its extracts at 32°C, toxin levels were negatively related to biomass, suggesting a possible physiological response to stress induced by the macrophyte or toxin release due to cell death and lysis. These findings indicate that temperature and nutrients complicate allelopathic interactions between macrophytes and cyanobacteria, and that E. densa extracts hold promise for controlling toxic blooms of R. raciborskii in a warmer and more eutrophic future.