Plant Growth Regulators Enhance Wheat Yield Under Shading Conditions by Optimizing Stem Sugar Metabolism and Lodging Resistance

Shading in agroforestry systems reduces light availability and increases the risk of lodging, limiting wheat (Triticum aestivum L.) yield. A two-year field experiment was conducted to assess the effects of chlormequat chloride (CCC) on wheat stem morphology, carbohydrate metabolism, lignin biosynthesis, lodging resistance, and yield under four shading intensities (S0: natural light; S1: 10% → 25% shading; S2: 20% → 50% shading; S3: 30% → 75% shading) from jointing to maturity stage. Shading resulted in taller plants with increased center of gravity, thinner stems, and reduced lignin, cellulose, and soluble sugar content, weakening stem-breaking strength and reducing yield. CCC application decreased internode length, increased stem solidity, and enhanced lignin and cellulose accumulation, as well as lignin biosynthesis enzyme activity. These changes improved stem-breaking strength and lodging resistance. Moreover, CCC significantly increased wheat yield by 2.7% to 23.3% (p < 0.05) depending on the shading intensity, and there was a significant interaction between shading intensity and CCC application on wheat grain yield (p < 0.05) The results demonstrate that CCC application can mitigate shading-induced yield loss by enhancing lodging resistance and improving stem integrity under the artificial-shading conditions evaluated in this study. Its effectiveness in actual agroforestry systems requires further field validation.