Microalgae‐Based Soil Amendment Promotes Wheat Growth, Yield, and Physiological Responses Under Regulated Deficit Irrigation

Sustainable agricultural practices such as water‐saving irrigation techniques and environmentally friendly soil amendments are of great significance. Utilizing microalgae (MA) biomass as a soil amendment could enhance wheat growth while alleviating water stress. This study evaluated the effects of regulated deficit irrigation (RDI) and MA biomass on wheat growth, soil fertility, and physiological responses. Two RDI regimes were tested: slight deficit irrigation (SDI 90% ) and moderate deficit irrigation (MDI 60% ), alongside four MA concentrations (0.5%, 2%, 3.5%, and 5%) and control treatment. Results showed that SDI 90% outperformed MDI 60% in promoting wheat morphological growth, biomass, and enzyme activities. MA application at 5% yielded the greatest improvements, while MA0.5% had minimal effects. Malondialdehyde (MDA), hydroxide ion (OH − ), superoxide radical (O 2 − ), and proline were elevated under MDI 60% but were mitigated by SDI 90% and MA5%. Ultrastructural analysis of seeds showed MDI 60% resulted in undeveloped starch granules and protein matrix degradation, whereas SDI 90% and MA5% improved seed quality, promoting well‐formed granules and structural integrity. Leaf mesophyll cell damage observed under MDI 60% was alleviated with MA5%. Integrating MA biomass (5%) with SDI 90% optimizes wheat growth, enhances stress tolerance, and improves yield under water deficit. This offers a sustainable solution to boost crop resilience and productivity in water‐limited environments.