Dodangodage, C. AKasturiarachchi, J. CPerera, T.ARajapakshe, S.DNiyangoda, S.SHalwatura, R.U2026-08-172026-06-09Dodangodage CA, Kasturiarachchi JC, Perera TA, Rajapakshe SD, Niyangoda SS and Halwatura RU (2026) Biochemical shifts in Chlorella vulgaris via post-stationary magnesium sulfate stress: optimizing biomass for advanced bio-fertilizers. Front. Plant Sci. 17:1867866. doi: 10.3389/fpls.2026.18678661664462Xhttps://rda.sliit.lk/handle/123456789/5233Sustainable agriculture requires bio-fertilizers that improve both nutrient efficiency and soil resilience. Microalgae are promising candidates; however, conventional optimization using sodium chloride (NaCl) stress introduces phytotoxic sodium residues that limit soil application. To address this, a biphasic cultivation strategy for Chlorella vulgaris was developed using magnesium sulfate (MgSO4) as a dual-function stressor. Following the onset of a nitrogen-limited stationary phase (Day 18), the addition of 0.4 g L-¹ MgSO4 induced intracellular macromolecular accumulation. Biomass increased by 44.8% (2.810 ± 0.090 g L-¹), driven by intracellular densification, with enrichment in both total carbohydrate (42.15 ± 2.10%) and lipid (36.24 ± 1.11%) fractions. Substituting NaCl with MgSO4 eliminates the risk of sodium-induced phytotoxicity upon soil application, while simultaneously pre-loading the biomass with essential secondary macronutrients. Overall, this study demonstrates that targeted MgSO4-induced metabolic shifts can generate high-density, functionally enhanced, sodium-free microalgal biomass to serve as a potential bio-fertilizer feedstock.enbiphasic cultivationcarbohydrate enrichmentChlorella vulgarislipid accumulationmicroalgal bio-fertilizerosmotic stressArticlehttps://doi.org/10.3389/fpls.2026.1867866