Effects of drought stress on growth, physiology and bioactive compound accumulation in licorice (Glycyrrhiza spp.): a meta-analysis-based integrated evaluation

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Introduction Drought stress is a major environmental factor affecting the growth, physiological processes, and secondary metabolism of licorice ( Glycyrrhiza spp .). However, the integrated responses of licorice to drought stress remain unclear. Methods This meta-analysis synthesized evidence from multiple studies to evaluate the effects of drought stress on growth, physiology, and bioactive compounds in licorice. Random forest analysis and partial least squares path modeling (PLS-PM) were further applied to identify influential predictors and potential pathway relationships. Results Drought significantly inhibited photosynthesis and growth. Net photosynthetic rate, stomatal conductance, and transpiration rate decreased by 38.31%, 27.74%, and 36.12%, respectively, while chlorophyll a, chlorophyll b, and SPAD values decreased by 20.83%, 27.52%, and 20.07%, respectively. Seed germination and shoot fresh weight were also reduced. Osmotic adjustment and antioxidant defenses were activated, with proline, soluble protein, and superoxide dismutase activity increasing by 79.82%, 41.30%, and 12.10%, respectively. However, malondialdehyde content increased by 52.90%, indicating insufficient protection against membrane lipid peroxidation. Bioactive compounds showed component-specific responses: total flavonoids increased by 14.97%, glycyrrhizic acid showed no significant overall change, and liquiritin declined in some subgroups. Drought intensity and soil water content were important predictors across physiological response categories, whereas treatment duration was particularly important for photosynthetic responses and bioactive compound accumulation. Discussion Overall, licorice responses to drought involved photosynthetic inhibition, osmotic adjustment, antioxidant defense, and secondary metabolic reprogramming. Increases in individual phenolic compounds should not be interpreted as an overall improvement in medicinal quality, particularly when accompanied by photosynthetic inhibition, oxidative damage, and biomass loss.