Root-Zone Temperature Drives Coordinated Photosynthesis, Root Architecture, and Metabolism Responses in <i>Schisandra chinensis</i> (Trucz.) Baill

Soil warming due to climate change has a significant potential impact on crop yield and quality. <i>Schisandra chinensis</i> (Trucz.) Baill, a multipurpose plant disseminated in the highly climate-sensitive region of Northeast Asia, is affected by soil warming, which limits the supply and quality of raw materials. This study investigated the differential responses of biomass accumulation and bioactive ingredient production across various organs to root-zone temperature (RZT) variations, employing both physiological assessments and metabolomic profiling. Elevated root temperatures may increase plant biomass and indirectly increase photosynthetic rates by promoting root growth; however, biomass responses differ among organs. A 20 °C root temperature promoted stem and leaf growth and inhibited root development, whereas a 30 °C root temperature significantly promoted root growth but reduced leaf biomass. Schisanhenol A, a key bioactive lignan serving as a quality marker for <i>S. chinensis</i>, displayed synthesis dependent on temperature. Concurrently, flavonoid biosynthesis is coordinated accumulation at the naringenin nodal point. A 15 °C RZT inhibited lignan production in roots while triggering stress-responsive phenol accumulation in leaves (41.39%). Conversely, at 20 °C and 30 °C RZTs, schisanhenol synthesis was repressed in leaves but accumulated in roots (9.8–25.71%). It is worth noting that the increase in RZT significantly promoted the synthesis and accumulation of schisandrol A in the aboveground part of the plant (43.88%). This research underscores that a suitable elevation in root-zone temperature can augment the medicinal attributes of the aerial components of <i>S. chinensis</i>.