Improving plant tolerance to water stress through beneficial soil microorganisms is a promising strategy in sustainable agriculture. This study evaluated the effects of Trichoderma isolates on growth, osmolytes, and nutrient status of the medicinal plant licorice (Glycyrrhiza glabra L.) under drought stress, using a factorial experiment in a completely randomized design with four replications. Plants, inoculated with T. harzianum (T25), T. viride (T36), or left non-inoculated (control), were subjected to three irrigation regimes: 90–100% (control), 60–70% (moderate stress), and 40–50% (severe stress) of field capacity (FC) for two months.
Drought stress markedly reduced shoot dry and fresh weights, root and shoot lengths, leaf area, relative water content (RWC), and chlorophyll a, b, and total chlorophyll contents, especially under severe stress. Inoculation with both isolates, significantly improved these growth traits and chlorophyll contents under drought stress. Application of the fungal isolates, particularly T36, significantly enhanced soluble sugar contents in shoots (36.47%) and roots (5.24%) as well as the uptake of phosphorus (134.80%), potassium (43.57%), magnesium (41.85%), zinc (14.45%), and iron (16.07%) under severe drought. Inoculated plants also exhibited lower levels of proline, carotenoids, and malondialdehyde in both shoots and roots compared to non-inoculated controls at both stress levels. These results indicate that Trichoderma improves licorice performance under drought through osmotic adjustment, reduced oxidative stress, and improvement of nutritional status. Overall, the findings highlight the potential of T36 as a promising inoculant for mitigating drought effects in licorice under controlled conditions, which warrants further validation under field conditions.
