Abstract
Abstract Aim To assess the allelopathic effects of the submerged macrophyte Ceratophyllum demersum on four strains of phytoplankton species: two cyanobacteria (Microcystis aeruginosa - microcystin producing and M. panniformis - non-microcystin producing), and two chlorophytes (Ankistrodesmus falcatus and Raphidocelis subcapitata). Methods A coexistence experiment between C. demersum and the four strains was carried out for six days, with eight treatments and three replicates. The strains were cultivated in ASM1 culture medium, under controlled laboratory conditions. Two treatments were assigned for each strain, one with 6 g.L-1 of the macrophyte, and the control without the plant. Biomasses and growth rates of the strains were evaluated every two days, which were compared through the T-test and two-way ANOVA, respectively. Results The results varied among the strains, with toxic M. aeruginosa being intensely inhibited by C. demersum, with a decrease of 99.5% in its biomass (p<0.001), while non-toxic M. panniformis was less affected by the allelochemicals, with a reduction of 86.2% (p<0.001). Ankistrodesmus falcatus delayed its growth when in coexistence with the macrophyte, decreasing its biomass in 50.4% (p<0.01), while R. subcapitata was not altered (p>0.05). In coexistence with C. demersum, M. aeruginosa exhibited the lowest growth rates (-0.65 d-1), followed by M. panniformis (-0.15 d-1), A. falcatus (0.19 d-1), and R. subcapitata (0.34 d-1), with significant differences between all strains (p<0.001). Microcystis aeruginosa presented higher inhibition rates than M. panniformis (p<0.001), as well as, A. falcatus was more inhibited than R. subcapitata (p<0.05). Conclusions The presence of microcystins could influence the allelopathic responses of C. demersum, that may release more allelochemicals in coexistence with toxic strains of M. aeruginosa. Accordingly, C. demersum can be used in biomanipulation strategies to control toxic and non-toxic cyanobacterial blooms, without damaging other phytoplankton species, like chlorophytes.
Highlights
In the last few decades, the rising temperatures linked to an excessive input of nutrients in the water bodies have supported the occurrence of cyanobacterial blooms (Kosten et al, 2012; Paerl & Otten, 2013)
The World Health Organization (WHO) and the Brazilian Ministry of Health established a tolerable limit of 1.0 μg.L-1 of microcystins in waters destined for public supply (Chorus & Bartram, 1999; Brasil, 2011)
The biomass of the toxic M. aeruginosa strain was inhibited from the second day of coexistence with C. demersum to the end of the experiment, reaching a biomass close to zero on the sixth day (Figure 1a)
Summary
In the last few decades, the rising temperatures linked to an excessive input of nutrients in the water bodies have supported the occurrence of cyanobacterial blooms (Kosten et al, 2012; Paerl & Otten, 2013). These blooms have become a frequent global problem for the public supply reservoirs, which can be composed of species that produce cyanotoxins, such as hepatotoxins, neurotoxins, and dermatotoxins (Wiegand & Pflugmacher, 2005). The World Health Organization (WHO) and the Brazilian Ministry of Health established a tolerable limit of 1.0 μg.L-1 of microcystins in waters destined for public supply (Chorus & Bartram, 1999; Brasil, 2011). In the Brazilian Semiarid region, the occurrence of microcystin‐containing cyanobacteria blooms is still more recurrent (Bittencourt-Oliveira et al, 2014; Lorenzi et al, 2018), which is certainly due to the climatic and eutrophication conditions of the water bodies in this region that favor the occurrence and establishment of these blooms (Moura et al, 2018)
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