Inhibition of growth rate and cylindrospermopsin synthesis by Raphidiopsis raciborskii upon exposure to macrophyte Lemna trisulca (L).

Impact of macrophyte Lemna trisulca on the growth rate and synthesis of cylindrospermopsin (CYN) by cyanobacterium Raphidiopsis raciborskii was determined. The presence of L. trisulca inhibited the biomass accumulation of the cyanobacterium by 25% compared to the control during co-cultivation. The simultaneous cultivation of these organisms slightly affected the inhibition of macrophyte growth rate by 5.5% compared to the control. However, no morphological changes of L. trisulca after incubation with cyanobacteria were observed. It was also shown that the long-term (35 days) co-cultivation of R. raciborskii and L. trisulca led to a decrease in CYN concentration in media and cyanobacterial cells by 32 and 38%, respectively, compared to the values obtained for independent cultivation of cyanobacterium. Excessive absorption of phosphate ions by L. trisulca from the medium compared to nitrate ions led to a significant increase in the nitrate:phosphate ratio in the media, which inhibits the development of cyanobacterium. The obtained results indicate that L. trisulca in the natural environment may affect the physiology of cyanobacteria. The presented study is the first assessment of the allelopathic interaction of macrophyte and R. raciborskii.