From waste to resource: agricultural potential of Limnospira platensis (spirulina) leftovers in chicory cultivation

Abstract Large-scale production of Limnospira platensis (spirulina) for high-value compounds such as C-phycocyanin generates substantial amounts of underexploited residual biomass. Aligned with circular economy, this study evaluated the agricultural upcycling of industrial L. platensis residual biomass (POST) as a biofertilizer comparing its effects with intact biomass (PRE) and a commercial fertilizer on germination, growth, and physiology of Cichorium intybus under laboratory and greenhouse conditions. Composition analyses showed that POST biomass retained high levels of nitrogen, phosphorus, and proteins despite phycocyanin extraction. Germination assays revealed that POST biomass (5 mg mL⁻ 1 concentration) did not exert phytotoxic effects and significantly enhanced germination, whereas PRE biomass induced inhibitory effects at higher doses. Germination dynamics showed an initial delay followed by equal or improved final germination, suggesting a priming-like response induced by POST biomass. Growth experiments demonstrated that POST biomass markedly promoted plant development, outperforming both PRE biomass and the commercial fertilizer. Fresh weight increases were dose-dependent and pronounced under greenhouse conditions, indicating robustness under environmentally variable settings. Consistently, POST biomass significantly enhanced chlorophyll and carotenoid contents, supporting improved photosynthetic performance. In contrast, PRE biomass showed weaker and less consistent effects. Phenolic and flavonoid contents revealed no stress-related accumulation in POST-treated plants, confirming the absence of adverse physiological responses. Overall, these findings demonstrate that industrial L. platensis leftovers retain significant bioactivity and can be effectively upcycled into sustainable agricultural product. The integration of agricultural reuse into Spirulina biorefinery chains represents a promising strategy to improve the environmental and economic sustainability of cyanobacterial production systems. Key Points • Limnospira platensis (spirulina) leftover biomass (POST) showed no phytotoxicity on Cichorium intybus seeds. • POST biomass administration (10 mg/mL) increased plant fresh weight up to 170%. • POST biomass administration increased plant pigment both laboratory and greenhouse. • Limnospira platensis downstream leftover showed potential as biofertilizer in agriculture.