Microalgae are unicellular micro-organisms capable of surviving in diverse
environmental conditions, including wastewater, digestate, and other effluents.
Therefore, they often play a role in the circular economy. Microalgae have the potential
to biostimulate plant growth and development and increase resistance to abiotic and
biotic stressors. In this study, we conducted laboratory experiments to evaluate the
biostimulatory effect of microalgae on cucumber (Cucumis sativus) and white mustard
(Sinapsis alba). In the experiment, we used a suspension of microalgae at a
concentration of 2g/L, with deionized (dH2O) as a control. The results with white
mustard showed a positive biostimulatory effect on aboveground plant growth, in
contrast to roots where no such effect was observed. In addition, we found that the
presence of nitrate nitrogen (NO3-N) in the microalgae suspension did not significantly
affect the initial growth of white mustard. Our studies revealed that the synthetic auxin
hormone indole-3-butyric acid (IBA) had no effect on adventitious root formation in
cucumbers. Conversely, cucumbers treated with microalgal suspensions showed
biostimulatory effects on adventitious root formation, but these effects were not
necessarily due to auxins. The synthetic cytokinin hormone benzylaminopurine (BAP)
showed no significant effect on cotyledon growth in cucumbers, nor did the microalgae
treatment. From the results, it can be concluded that microalgae have different
biostimulatory effects depending on the plant species or plant organ studied.
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