Numerous studies showed that the growth of medicinal plants in their native areas was simultaneously affected by abiotic stress combinations. Compared with single stress, plants have unique responses to a combination of different abiotic stresses and cannot be inferred directly from plants' responses to each individual stress. The effect of combined stresses on plants usually has three types of synergistic antagonism or independence. The secondary metabolism in the process of medicinal plant stress combination response also played a vital role, and environmental stresses can spur the accumulation of secondary metabolites, but under the stress combination, plants induce specific gene expression of key enzymes on secondary metabolic pathways, in turn, the accumulation of secondary metabolites against stress is formed. When plants are subjected to stress combination, the interaction of multiple signaling pathways makes it highly complex for plants to respond to stress combination. This paper summarized the effects of stress combination on physiological and secondary metabolism of medicinal plants, and discussed the related physiological, biochemical and molecular mechanisms. It provides theoretical basis for improving the adaptability of medicinal plants to adversity, improving the quality of Chinese medicinal materials, and further optimizing the cultivation of medicinal plants.
Keywords: medicinal plant; physiological response; secondary metabolites; stress combination; stress resistance.