Sucrose and pipecolic acid-mediated enrichment of rhizosphere Rhizobiale-Burkholderiale bacteria improves soybean growth under low-light conditions.

Low light (LL) limits the productivity of intercropped and densely planted legumes and also affects root-associated microbial communities. However, how LL reshapes root-microbe interactions and whether the root microbiota can mitigate LL-induced damage in legumes remain unclear. Here, a meta-analysis based on field observations revealed that negative effects predominated (>70%) in intercropped and densely planted legume systems, with light intensity emerging as the strongest predictor of yield variation. Using soybean as a model, we found that LL suppressed photosynthesis, biomass accumulation, and nodulation and that these effects were further aggravated in sterilized soil. Furthermore, soil transplantation experiments showed that soils conditioned by LL-grown plants reduced subsequent plant biomass. Compared with normal light, LL shifted rhizosphere microbial assembly toward a more deterministic process, reduced bacterial diversity, and simplified bacterial co-occurrence networks, with Rhizobiales and Burkholderiales showing significantly lower relative abundances. Metabolomic analysis identified sucrose and pipecolic acid as LL-responsive metabolites whose abundances were strongly correlated with the relative abundances of these taxa. Chemotaxis and growth assays revealed that sucrose functions as both a carbon source and a chemoattractant, whereas pipecolic acid acts as a chemoattractant. Reintroduction of representative isolates or simplified synthetic microbial communities alleviated LL-induced growth inhibition by enhancing photosynthetic performance, modulating redox status, and reprogramming host transcriptional responses. Together, our findings support a model linking root exudates, rhizosphere microbiota, and plant performance under LL and highlight the potential of microbiome-based strategies to improve crop production in LL environments.