Biostimulant effect of a novel seawater-adapted strain of Scenedesmus almeriensis on garden geranium

Microalgae production requires substantial water resources. For this reason, different strategies are being investigated such as cultivating microalgae using wastewater or seawater. The goal of this study was to demonstrate the biostimulant effect of Scenedesmus almeriensis produced using both freshwater and seawater. This is the first time that the biostimulant capacity of seawater-produced Scenedesmus almeriensis has been investigated. The biostimulant capacity of the biomass was assessed in vitro using different bioassays and validated in vivo using Pelargonium × hortorum, commonly called zonal geranium or garden geranium. The in vitro results showed that S. almeriensis extracts significantly improved the germination index (GI) in watercress seeds and stimulated root formation in soybean seedlings compared to the water control. The in vivo trials confirmed that plants treated with S. almeriensis extracts experienced significant increases in the height, number of leaves and flowers, and dry weight of various organs, indicating an overall improvement in plant biomass and structural health. The results also revealed that the biomass produced in freshwater was more effective than that obtained in seawater, probably due to a lower accumulation of saline compounds that can reduce the biostimulant activity. •The freshwater microalga S. almeriensis was produced using seawater.•The biostimulant effects of the biomass were assessed in vitro and in vivo.•The biomass produced using freshwater showed higher biostimulant effects.•The biomass promoted seed germination and root formation in vitro.•Geranium plants treated with S. almeriensis showed improved quality.