Seaweed extracts are widely used as biostimulants in terrestrial crops but remain underexplored for economic macroalgae. This study investigated the effects of Ascophyllum marine plant extract powder (AMPEP) and Saccharina japonica extract powder (SJEP) on the growth and stress resistance of Pyropia yezoensis, a commercially significant red macroalga along the Northeast Asia coast. Through gradient analysis, optimal concentrat...