Physiological Mechanisms of an Exogenous Compound Agent in Alleviating High‐Temperature Stress in Rice ( <i>Oryza sativa</i> L.) During the Flowering Stage Through Multi‐Target Synergistic Regulation

ABSTRACT High‐temperature stress during the flowering stage, exacerbated by climate change, has become a major abiotic constraint on global rice production. This study aimed to identify effective mitigation strategies by systematically evaluating the physiological effects of exogenous compound agents on rice under high‐temperature stress at flowering. A heat‐tolerant cultivar (N22) and a heat‐sensitive cultivar (YR343) were subjected to high‐temperature stress during flowering, and 17 different formulations comprising calcium chloride (CaCl 2 ), salicylic acid (SA), abscisic acid (ABA) and potassium dihydrogen phosphate (KH 2 PO 4 ) were applied. The results showed that high‐temperature stress significantly reduced pollen viability, the net photosynthetic rate ( P n ), and the activities of peroxidase (POD) and catalase (CAT), while increasing malondialdehyde (MDA) content, ultimately leading to significant decreases in the seed‐setting rate and yield. In contrast, exogenous compound treatments effectively alleviated this physiological damage. Among them, the ternary formulations ABC (CaCl 2 + SA + ABA) and ABD (CaCl 2 + SA + KH 2 PO 4 ) were the most effective. The underlying physiological mechanisms involve the synergistic regulation of three key processes: first, improving anther carbohydrate metabolism and increasing pollen stainability, thereby stabilising the seed‐setting rate; second, slowing chlorophyll degradation and maintaining a higher P n to ensure photosynthetic productivity; and finally, synergistically enhancing the activities of antioxidant enzymes (POD, CAT) and promoting the accumulation of osmotic regulators (e.g., soluble sugars and proteins), thereby reducing oxidative damage and maintaining cell membrane stability. This study demonstrates that foliar application of ABC or ABD can systematically enhance thermotolerance during flowering through multi‐target synergistic effects. These findings not only elucidate the physiological mechanisms of crop responses to high temperature but also propose a feasible agronomic strategy to mitigate heat‐induced yield losses.