Effects of extraction methods on the plant biostimulant activity of the soil microalga Chlorella vulgaris

Abstract

The increased demand for sustainable and ecological agricultural tools to decrease the dependency on chemical fertilizers has surged throughout the last years. Cyanobacteria and microalgae-based biostimulants offer an innovative solution and ecofriendly platform for plant biostimulant production, due to their metabolic diversity and valuable value-added products. Focuses were directed especially towards marine and freshwaters microalgae whereas indigenous soil microalgae were rarely prospected for their biostimulant potential. The aim of this study was to assess the biostimulant activity of the soil microalga Chlorella vulgaris on seed germination performance. The effects of extraction method and plant choice on the biostimulant activity of C. vulgaris were investigated via the comparison of the composition and activity of four extraction techniques (aqueous extraction, acid hydrolysis extraction, organic solvent extraction, microwave-assisted aqueous extraction) on two different plant seed models (wheat and tomato). Seeds were soaked with four different concentrations (from 0.1 g L⁻¹ to 2 g L⁻¹) to determine dose-dependent effects. Results demonstrated significant differences in extracts biochemical composition and biostimulant effects on seed germination enhancement. Extract composition in terms of biomolecules concentrations revealed significant dissimilarities. Seed germination indices and biometric parameters were significantly improved by lower doses (0.1 g L⁻¹ and 1 g L⁻¹), while higher doses (2 g L⁻¹) usually revealed negative effects. The best increases in wheat and tomato seed germination parameters were reached by using acid hydrolysis, aqueous and microwave-assisted aqueous extracts at lower doses. Thus, our results highlight that aqueous extract-based methods were as effective as other techniques. These findings shed light on the advantages of eco-extraction processes and microalgae-based aqueous extracts as eco-friendly biostimulants eligible for sustainable agriculture.