Effects of drought stress on photosynthetic characteristics and root water absorption of Glycyrrhiza uralensis

Glycyrrhiza uralensis is a perennial herb in the legume family. G. uralensis has high medicinal value and is an important economic and ecological crop in arid and semi-arid areas. Soil moisture is one of the main environmental factors limiting the growth of G. uralensis. Studying its drought resistance adaptability is essential for the sustainable use of licorice resources. In this study, polyethylene glycol 6000 (PEG-6000) was used to simulate drought stress, and the photosynthetic characteristics and root water absorption capacity of G. inflata and G. uralensis seedlings were examined. After seven days of drought stress, the shoot dry weight and root dry weight of G. inflata and G. uralensis seedlings decreased significantly. The shoot dry weight of each tested variety decreased by 56.10% and 62.50%, respectively. The root dry weight decreased by 16.67% and 28.57%, respectively. Moreover, the root shoot ratio increased. Drought stress decreased the net photosynthetic rate (P_n), transpiration rate (T_r), and stomatal conductance (G_s) of G. inflata and G. uralensis seedlings. Compared to the control, the decrease was 41.73%, 67.22%, 62.21%, 75.38%, 66.02%, and 82.60%. The fluorescence characteristics of G. uralensis seedlings were also significantly inhibited under drought stress. When compared to the control, the potential activity of photosystem Ⅱ (F_v/F_o) and maximal photochemical efficiency (F_v/F_m) of G. inflata seedlings decreased by 21.94% and 9.09%, respectively. When compared to the control, the F_v/F_o and F_v/F_m of G. uralensis seedlings decreased by 35.10% and 10.39%, respectively. The photochemical quenching coefficient (qP) of G. inflata and G. uralensis seedlings decreased by 17.65% and 27.27% under 15% PEG stress, respectively. Drought stress reduced the relative water content and leaf water potential of the two G. uralensis seedlings. The relative water content of the leaves of G. inflata seedlings decreased by 11.07% and the leaf water potential decreased by 19.54%. The relative water content of leaves of G. uralensis seedlings decreased by 13.91%, and the leaf water potential decreased by 62.56%. Drought stress inhibited root growth and decreased the root surface area and volume but increased the total root length in both G. uralensis species. The root of G. inflata was significantly smaller than that of G. uralensis. However, the hydraulic conductivity of the whole root of G. inflata decreased less than that of G. uralensis under drought stress. The findings demonstrate that G. inflata can have higher photosynthetic advantages during drought stress. Its smaller roots have higher root efficiency, which enhances agricultural water use efficiency through stronger root water absorption capacity and stronger drought resistance. This research can provide a basis for supplementing and improving the drought tolerance of G. uralensis and provide strategies for artificial cultivation, protection, and use of xerophyte resources.