Comparative effects of Kappaphycus alvarezii biostimulants from southern and southeastern Brazil on the biochemical profile of hydroponically grown peppermint (Mentha x piperita L.)

This study aimed to evaluate the morphological and biochemical responses of peppermint (Mentha x piperita L.) plants grown in a deep-water hydroponic system, following foliar application of the Kappaphycus alvarezii biostimulant (Kal). For this purpose, Kal samples produced in southern (Santa Catarina state – Kal-SC) and southeastern (São Paulo state – Kal-SP) Brazil were collected and weekly applied via foliar spraying at 1%, 3%, 5%, and 7% (v/v) concentrations at the end of the cultivation period, morphological traits, biochemical parameters, and the biogenic amine profile of peppermint plants were assessed. No statistically significant differences (p < 0.05) were observed in the morphological parameters, including plant height, root length, number of nodes, and shoots and root biomass, between Kal-treated plants and control. However, significant differences were detected across all biochemical parameters investigated, with increased contents of total soluble sugars, starch, carbohydrates, proteins, amino acids, and flavonoids in plants treated with both Kal-SP and Kal-SC in comparison to control. Treatments with Kal-SP at 3% and 5% and Kal-SC at 3%, 5%, and 7% were the more effective in modulating the biochemical and metabolic responses of peppermint plants. Additionally, the algal biostimulant influenced the biogenic amine profile, indicating a positive effect on secondary metabolism. These findings support the potential of K. alvarezii biostimulants to enhance biochemical performance in peppermint plants grown in a hydroponic system, improved plant quality regarding their contents of primary and secondary metabolites.