Drought-tolerant Sedum for extensive green roofs: insights into visual performance selection and integrated responses to water withholding

Selecting drought-tolerant Sedum species based on visual performance is crucial for maintaining the plants’ favorable contribution to landscape and ecosystem services in extensive green roofs (EGRs) that are frequently subjected to long-term water withholding. Current understanding of the adaptive strategies of Sedum species in response to water withholding, particularly regarding transcriptomics and metabolomics, remains limited. In this study, the visual performance and morphological, biochemical, and physiological indicators of four Sedum species under 50-day water withholding were measured, and the transcriptomic, metabolomic, and integrated multi-omics analyses were further conducted on the leaves and roots of the optimal drought-tolerant Sedum species. S. lineare Thunb. with better visual performance under 50-day water withholding was identified as the optimal drought-tolerant species. Notably, the response strategies of the four Sedum species to water withholding exhibited species-specific patterns across different indicators, and root length, root-shoot ratio, leaf water content, and photosynthetic-fluorescence indicators (excluding phosphoenolpyruvate carboxylase activity) were their key response indicators correlated with visual performance and dominant in the water-depletion stage. Transcriptomic and metabolomic analyses revealed that roots primarily upregulated the gene expression of α-galactosidase, UDP-glucose 4-epimerase, and galactinol synthase to enhance the synthesis of sucrose, trehalose, and raffinose to adapt to water decline. Our findings systematically advance the current understanding of water-withholding adaptation strategies in Sedum and provide reliable theoretical support for identifying prospective breeding targets and candidate genes for drought-tolerant Sedum, thereby promoting low-maintenance and sustainable EGR implementation.