Seasonal changes in phytohormones, flavonoids, and antioxidant activity of two macroalgae from the Ecuadorian coast

The use of seaweed or macroalgae as plant biostimulants has increased in recent years. This study discusses the effect of seasonal sea temperatures on the phytohormone and flavonoid contents, and the antioxidant activity of Acanthophora spicifera and Ulva intestinalis from Ecuador. For the extraction, aqueous digestion (AD), ethanol digestion (ED), ethanol sonication (ES), and methanol digestion (MD) were used. Metabolites and antioxidant activity were quantified by liquid chromatography and spectrophotometry. Multivariate analysis revealed that U. intestinalis exhibited enhanced flavonoid (up to 67.73 mg/kg) and phytohormone (up to 20.79 mg/kg) accumulation in the dry season, while the antioxidant capacity (TPC, TFC, DPPH, and FRAP) increased during the wet season. Conversely, A. spicifera showed a slight increase in phytohormone levels (up to 8.68 mg/kg) during the wet season, particularly in 3-indoleacetic acid, and gibberellic acid. These findings contribute first insights into antioxidant responses to seasonal changes.