Optimization of Intercropping Modes in <i>Placodon grandiflorus</i>

Intercropping enhances plant growth, increases yield, and boosts the accumulation of secondary metabolites. <i>Platycodon grandiflorus</i> (<i>P. grandiflorus</i>), a traditional Chinese medicinal herb, has limited research available regarding its intercropping practices. We aimed to (1) examine the changes in the physiological and biochemical indicators of plant growth during the intercropping process of <i>P. grandiflorus</i>, (2) assess the quality of <i>P. grandiflorus</i> when intercropped with different crops, and (3) evaluate the optimal intercropping mode for <i>P. grandiflorus.</i> This study utilized the two-year seedlings of <i>P. grandiflorus</i> as the test material in a field study. The intercropping treatments included <i>P. grandiflorus</i> monoculture (JG-JG), intercropping with <i>Achyranthes bidentata</i> (JG-NX), <i>Saposhnikovia divaricata</i> (JG-FF), <i>Adenophora stricta</i> (JG-SS), <i>Zea mays</i> (JG-YM), <i>Setaria italica</i> (JG-GZ), and <i>Glycine max</i> (JG-DD). We investigated the effects of these different intercropping modes on the growth, physiological and biochemical indicators, and the accumulation of five saponins in <i>P. grandiflorus</i> at various growth and development stages. Compared with JG-JG, the chlorophyll and the MDA contents significantly increased and decreased, respectively, in the JG-YM, JG-DD, and JG-NX treatments. All the three treatments enhanced the biomass and exhibited the higher levels of antioxidant enzyme activity and osmoregulatory substance content. JG-YM and JG-SS significantly (<i>p</i> < 0.05) improved the quality of <i>P. grandiflorus</i>, with JG-SS intercropping notably maintaining a high content of platycodin D. The results of this study provide a scientific basis for optimizing intercropping planting systems and advancing the sustainable development of the traditional Chinese medicine industry.