Forchlorfenuron as a Safe Growth Regulator Significantly Improves Yield and Quality of Glycyrrhiza uralensis

The yield and quality have long been constraining factors for the sustainable cultivation of Glycyrrhiza uralensis. This study evaluated the effects of foliar applications of forchlorfenuron (CPPU) at different concentrations (0, 5, 10, 20, and 40 mg·L−1) on plant growth and secondary metabolism through comprehensive analyses of photosynthesis, endogenous phytohormones, root biomass, and medicinal components. To ensure consumer safety, CPPU residue dynamics and associated health risks were also assessed. The 10 mg·L−1 treatment yielded the most pronounced improvements, increasing root biomass by 46%, glycyrrhizic acid content by 92%, and liquiritin content by 98.7%. It also enhanced the activity of ribulose-1,5-bisphosphate carboxylase, thereby improving overall photosynthetic gas exchange capacity, and significantly stimulated the synthesis of zeatin, abscisic acid, and salicylic acid. Residue analysis showed that by the 56th day after treatment, the CPPU level in roots was merely 5.44 × 10−4 mg·kg−1, with a half-life of 11.74 days. The resulting risk quotient (RQ) was below 0.01%, well under the safety threshold of 1, indicating negligible health risk to consumers. Our results demonstrate that the targeted application of CPPU offers a highly effective and safe strategy for enhancing both the productivity and commercial quality of G. uralensis.