Alfalfa Biostimulated with Desmodesmus sp.: A Link between Effluent Treatment and Sustainable Agriculture to Improve Plant Growth and Quality

This study evaluated the application of algal biomass as a biostimulant in Medicago sativa (alfalfa). The biomass was obtained from the selection and cultivation of the microalga Desmodesmus sp., isolated from an urban river. This biomass was applied at different concentrations to alfalfa seeds: Control: irrigation with distilled water, treatments A (Ta), B (Tb), C (Tc) irrigation with 2.5% ,5% and 7.5% algal solution respectively and seedlings: control: distilled water and treatments A (Ta), B (Tb) C (Tc) 5%, 10%, 15% algal solution respectively. There were no significant differences in the germination parameters The statistically significant increase in radicle length, with a p<0.001, was observed in the treatment with 2.5% and 5% algae versus the control. Fresh root weight showed a significant increase in treatment A (5%) and B (10%) with values **p < 0.01 and *p < 0.05, respectively. Root length showed a highly significant increase in plants treated with solutions A, B and C (***p<0.001). Aerial dry weight showed a significant increase in treatment A and the root dry weight in treatments A and C compared to the control. The effect was beneficial for root and root elongation, root dry and fresh biomass, and leaf dry biomass; in addition to a significant increase in photosynthetic pigments, indicating greater photosynthetic activity. These results demonstrate that native microalgae cultivated in wastewater can function as effective biostimulants in alfalfa, offering a circular bioeconomy strategy that integrates environmental remediation with agricultural productivity.