AbstractMicroalgae biomass exploitation as a carbon–neutral energy source is currently limited by several factors, productivity being one of the most relevant. Due to the high absorption properties of light-harvesting antenna, photosynthetic cells tend to capture an excessive amount of energy that cannot be entirely channeled through the electron transfer chain that ends up dissipated as heat and fluorescence, reducing the overall light use efficiency. Aiming to minimize this hurdle, in this work we studied the effect of decreasing concentrations of Magnesium (Mg²⁺) on the chlorophyllacontent, photosynthetic performance, biomass and lipid production of autotrophic cultures ofBotryococcus brauniiLB 572. We also performed, for the first time, a comparative lipidomic analysis to identify the influence of limited Mg²⁺supply on the lipid profile of this algae. The results indicated that a level of 0.0037 g L⁻¹MgSO₄caused a significant decline on chlorophyllacontent with a concomitant 2.3-fold reduction in the biomass absorption coefficient. In addition, the Mg²⁺limitation caused a decrease in the total carbohydrate content and triggered lipid accumulation, achieving levels of up to 53% DCW, whereas the biomass productivity remained similar for all tested conditions. The lipidome analysis revealed that the lowest Mg²⁺concentrations also caused a differential lipid profile distribution, with an enrichment of neutral lipids and an increase of structural lipids. In that sense, we showed that Mg²⁺limitation represents an alternative optimization approach that not only enhances accumulation of neutral lipids inB. brauniicells but also may potentially lead to a better areal biomass productivity due to the reduction in the cellular light absorption properties of the cells.