Developing an efficient intercrop system for understory medicinal plant cultivation: allelopathy- based screening of...

Allelopathy is a common regulatory interaction among plants in nature, understanding these allelopathic interactions offers a promising bio-tool for guiding or designing productive and sustainable agroforestry systems. However, due to species-specific differences, how to quantitatively and systematically select appropriate nurse trees based on allelopathic effects to optimize understory cultivation of medicinal plants remains largely unclear. This study evaluated the potential of utilizing allelopathic effects of rhizosphere soil aqueous extracts to select nurse trees for establishing efficient understory cultivation system for Turpinia arguta, a valuable shade-tolerant medicinal plant with substantial market demand. We tested the allelopathic effects of rhizosphere soil aqueous extracts from seven candidate companion tree species of T. arguta on its seed germination, seedling growth and cutting physiology. Results revealed a concentration-dependent allelopathic response: seed germination was optimally promoted at 0.25 g/mL of the aqueous extracts of Pinus elliottii and Camphora officinarum. Notably, the aqueous extract of P. elliottii consistently exhibited the greatest growth-promoting effects, significantly enhancing seedling root length, plant height and biomass (fresh and dry weight). For cuttings, the aqueous extracts generally promoted Pn and Tr, while low-concentration of aqueous extracts from P. elliottii, C. officinarum and Liquidambar formosana increased the actual photochemistry efficiency of PSII (YII), qP and ETR. Furthermore, MDA content, SOD, POD and CAT were dependent on both tree species and the concentrations of aqueous extracts. The synthetic allelopathic index confirmed P. elliottii as the most beneficial companion tree for T. arguta. Taken together, this study shows that P. elliottii has consistently positive allelopathic effects on T. arguta, promoting its seed germination and seedling growth, and these findings support an integrated P. elliottii- T. arguta understory planting system. Similar allelopathic evaluation approaches can be used to select optimal companion trees for other valuable medicinal plants in diversified agroforestry systems.