Morphological, physiological, and root metabolomic responses of Hemerocallis minor Mill. to drought stress

Drought stress is a major environmental factor limiting plant growth and ecosystem stability in arid and semi-arid regions. Hemerocallis minor Mill., a perennial herb with strong drought tolerance, has potential applications in ecological restoration and marginal land utilization. However, the coordinated relationships among morphological, physiological, and metabolic responses, as well as the response characteristics under different intensities of drought stress, remain poorly understood.

In this study, a 12-week gradient drought stress experiment was conducted. An integrated multi-parameter approach was applied to systematically evaluate the responses of H. minor to varying drought intensities at the levels of growth morphology, physiological traits, and root metabolism.

Morphologically, drought stress induced changes such as root thickening, whereas severe and extreme drought significantly inhibited plant height, root growth, and adventitious root formation. Physiologically, plants under moderate drought maintained relatively stable leaf water content and some physiological traits, while severe drought caused pronounced membrane damage and oxidative stress responses. Metabolically, drought stress substantially remodeled root metabolic networks, with numerous differential metabolites detected across comparison groups, primarily involving amino acids, flavonoids, and coumarins. Among them, 23 differential metabolites were annotated to the isoflavonoid biosynthesis pathway. Correlation analysis indicated significant associations between root morphological traits, physiological indicators, and key metabolites: proline, malondialdehyde (MDA), and peroxidase (POD) activity were negatively correlated with certain growth parameters, whereas some isoflavone glycosides and isoflavonoid metabolites were positively correlated.

This study provides a comprehensive "morphology-physiology -metabolism" perspective on the responses of H. minor to drought stress. Results indicate that under mild to moderate drought, plants maintain relatively stable growth and physiological status, whereas severe drought induces pronounced stress responses and metabolic adjustments. These response patterns likely contribute to the adaptation of H. minor to drought environments. The findings offer references for the selection and application of drought-tolerant plants in ecological restoration and marginal land utilization, while further validation of the underlying response mechanisms and ecological significance is warranted through anatomical, molecular, targeted metabolomic, and field studies.