Light Modulates Growth‐Resistance‐Quality Trade‐Offs in Pseudostellaria Heterophylla via a Light‐Induced Microbiota‐Root‐Shoot Axis

Plants rely on plant-microbiota interactions to balance growth, defence, and metabolism under stress. Still, the mechanisms governing growth-resistance-quality trade-offs in the shade-tolerant medicinal herb Pseudostellaria heterophylla in understory cultivation systems remain unclear. Here, we integrated phenotypic/photosynthetic/quality assays, rhizosphere microbiome sequencing, leaf transcriptomics, and plant-microbe co-culture experiments to study responses to graded shading. Shading enhanced yield and disease resistance, reshaped the microbiome (enriching beneficial taxa, suppressing pathogenic Alternaria), and induced transcriptional reprogramming-upregulating starch-sucrose/glycerophospholipid metabolism and downregulating flavonoid biosynthesis genes (CHI/CHS) to reduce root-exuded flavonoids that inhibit beneficial bacteria. Functional assays confirmed that these bacteria promote growth and suppress Alternaria-mediated disease under low light. Our findings demonstrate trade-offs in shading coordinates along a bidirectional microbiota-root-shoot axis, establishing a framework for sustainable understory medicinal plant cultivation.