The impact of algal extract as a biostimulant on cold stress tolerance in barley (Hordeum vulgare L.)

Cold stress, including chilling and freezing temperatures, poses significant challenges to plant growth and productivity in temperate and cold climates. Algal-derived biostimulants have been widely employed to mitigate various environmental stresses in plants. However, limited research has investigated the effect of algal extract on cold tolerance. In this study, we examined the impact of a 0.05% (w/v) water extract from two distantly related algae, Sargassum angustifolium (Sargassaceae, Phaeophyceae) and Haematococcus pluvialis (Haematococcaceae, Chlorophyceae), on barley (Hordeum vulgare) plants grown hydroponically under either control conditions (25/17 degrees C day/night temperature) or chilling stress (5/3 degrees C day/night temperature) for a duration of two weeks. While S. angustifolium extract improved plant biomass under control conditions, the algal extracts did not influence biomass under chilling stress. However, both algal extracts positively influenced photosynthetic parameters (leaf pigments and chlorophyll fluorescence) as well as biochemical indicators of cold stress, including proline, carbohydrates, phenolics, peroxidase activity, and phenylalanine ammonia lyase activity. Furthermore, the algal extract significantly reduced leaf injury and lethal temperature (LT50) under freezing stress (-10 degrees C and -15 degrees C). Notably, the extract from S. angustifolium, a warm water alga, exhibited slightly or significantly higher effectiveness in mitigating cold stress compared to the extract from H. pluvialis, a species adapted to cold and temperate climates. These findings suggest that the effectiveness of algal extracts in alleviating specific types of environmental stress is not solely dependent on the habitat from which the algae are derived.