Exploring the biofertilizer potential of Gracilaria birdiae aqueous extract for sustainable agriculture

Abstract

Macroalgal generates valuable bioproducts, primarily extracted using inorganic solvents. However, water can dissolve nutrients, offering an alternative for clean agriculture from a renewable inexpensive source. Therefore, the main objective of this study was to produce and characterize the aqueous extract of Gracilaria birdiae and evaluate its potential for enhancing plant growth. The first and second extraction stages presented 5.3 % and 11.5 % solid biomass, yielding 88.5 % of the final aqueous extract. Lyophilization preserved 0.3 % of initial weight and was the most effective storage condition for maintaining extract's compounds. Gas chromatography-mass spectrometry identified 54 metabolites in the algae extract, including organic acids (63.5 %), sugars and derivates (17.2 %), amino acids (14.5 %), and other compounds (3.9 %). The extract also retained high levels of macronutrients, including nitrogen (N), phosphorus (P), and potassium (K), 14.8, 16.0, and 276.7 g/kg, respectively along with macro and micronutrients. Rice plants sprayed with the aqueous extract showed a tendency to increase tiller number, carotenoids, carboxylation efficiency, and biomass. It was followed by a negative correlation with electrolyte leakage. The principal component analysis (PCA) showed the divergence of the control and treated groups, with axes representing 93.2 % of the variations. Overall, a water-based product can be considered for use as a potential biofertilizer or biostimulant due to its high nutrient content and abundance of organic molecules. The reduced electrolyte leakage may also indicate physiological conditioning or an antioxidant role. Nevertheless, future research should investigate the optimal percentages, frequencies, and methods for applying the extract.