Microalgae have emerged as promising environmentally friendly biostimulants, attributed to their diverse array of bioactive compounds. As the cultivation conditions of these microalgae can significantly affect their biochemical composition, understanding the impact of cultivation conditions on biostimulant activity exerted by the produced biomass can be a critical factor in support of a microalgae-based biostimulant industry. In this study, we investigated the effect of manipulating the initial pH and nitrate content of the cultivation medium on the growth, biomass yield and composition of Limnospira platensis (Spirulina). Our results indicated that while manipulating the initial pH did not affect any of the outputs (most likely due to pH convergence towards pH 10 observed for all samples during cultivation), varying the initial nitrate content produced biomass with significantly different biochemical profiles, expressed by their protein, phycocyanin, carbohydrate and lipid contents. These compositional changes occurred without significant differences in biomass yield. The consequences of such changes in (partially) disrupted biomass composition on their associated biostimulant activity were further tested in an Arabidopsis thaliana germination assay, in which we found that low-nitrate cultivated L. platensis outperformed its high-nitrate cultivated counterpart. Our study shows that L. platensis biomass composition and linked biostimulant activity can be tailored by manipulating the growth conditions. Hence, there is an understudied opportunity of optimizing the cultivation conditions of microalgae for targeted biostimulant applications.
Swinnen et al. (Sun,) studied this question.