La (NO3)3 substantially fortified Glycyrrhiza uralensis's resilience against salt stress by interconnected pathways

Abstract

The taproot of Glycyrrhiza uralensis is globally appreciated for its medicinal and commercial value and is one of the most popular medicinal plants. With the decline of wild G. uralensis resources, cultivated G. uralensis has become a key method to ensure supply. However, soil salinization poses challenges to G. uralensis cultivation and affects the yield and quality of it. In this study, the inhibitory effects of NaCl and Na₂SO₄ on yield and quality of G. uralensis were comprehensively evaluated in a three-year large-scale pot experiment, and the alleviating effects of supplementation with lanthanum nitrate (La (NO₃)₃) on G. uralensis were further evaluated under salt stress. The findings indicate that La (NO₃)₃ significantly strengthened the plant's salt tolerance by enhancing photosynthetic capacity, osmolyte accumulation, antioxidant defenses, and cellular balance of ions, which led to a substantial increase in root biomass and accumulation of major medicinal components. In comparison to the NaCl-stress treatment, the 0.75 M La (NO₃)₃ + NaCl treatment resulted in a 20% and 34% increase in taproot length and biomass, respectively, alongside a 52% and 43% rise in glycyrrhizic acid and glycyrrhizin content, respectively. Similar improvements were observed with 0.75 M La (NO₃)₃ + Na₂SO₄ treatment, which increased root length and biomass by 14% and 26%, respectively, and glycyrrhizic acid and glycyrrhizin content by 40% and 38%, respectively. The combined showed that application of La (NO₃)₃ not only significantly improved the salt resilience of G. uralensis, but also had a more pronounced alleviation of growth inhibition induced by NaCl compared to Na₂SO₄ stress except in the gas exchange parameters and root growth. This study provides a scientific basis for high-yield and high-quality cultivation of G. uralensis in saline soils and a new approach for other medicinal plants to improve their salt tolerance.

Keywords: Antioxidant system function; Ionic balance; Osmoregulatory capacity; Photosynthetic performance; Yield and quality.

Fig. 1

Variation in monthly temperature and precipitation (A) and sunshine duration (B)

Fig. 2

Map of the experimental plot

Fig. 3

Effects of La (NO₃)₃ on MDA concentration (a) and conductivity (b) of G. uralensis taproot under salt-free and salt-stressed treatments (mean ± SE). Different capital letters indicate significant differences under treatments (p < 0.05)

Fig. 4

Effects of La (NO₃)₃ on Pro (a), SS (b) and SP concentration (c) of G. uralensis taproot under salt-free and salt-stressed treatments (mean ± SE). Different capital letters indicate significant differences under treatments (p < 0.05)

Fig. 5

Effects of La (NO₃)₃ on Na⁺ (a), K⁺ (b), Mg²⁺ (c) and Ca.²⁺ concentration (d) of G. uralensis taproot under salt-free and salt-stressed treatments (mean ± SE). Different capital letters indicate significant differences under treatments (p < 0.05)

Fig. 6

Effects of La (NO₃)₃ on Pro (a), SS (b) and SP concentration (c) of G. uralensis taproot under salt-free and salt-stressed treatments (mean ± SE). Different capital letters indicate significant differences under treatments (p < 0.05)

Fig. 7

Effects of La (NO₃)₃ on glycyrrhizic acid and glycyrrhizin concentration (a) and total content of glycyrrhizic acid and glycyrrhizin per plant (b). of G. uralensis taproot under salt-free and salt-stressed treatments (mean ± SE). Different capital letters indicate significant differences under treatments (p < 0.05)

Fig. 8

Effects of La (NO₃)₃ on TL (a), MDT (b), ADT (c), TB (d) and R/S (e) of G.uralensis under salt-free and salt-stressed treatments (mean ± SE). Different capital letters indicate significant differences under treatments (p < 0.05)

Fig. 9

Effects of La (NO₃)₃ on taproot Lanthanum concentration of G. uralensis under salt-free and salt-stressed treatments (mean ± SE). Different capital letters indicate significant differences under treatments (p < 0.05)

Fig. 10

Correlations between La (NO₃)₃ and the properties of salt-tolerance of G. uralensis. In the correlation coefficient matrix, positive correlations are represented in blue, while negative correlations are indicated in red. The deeper the color and the larger the area of the rectangle, the higher the correlation between the two variables

Fig. 11

SEM of the direct or indirect effects of La (NO₃)₃ on the salt tolerance of Glycyrrhiza uralensis. (GFI = 0.828; CFI = 0.982; RMR = 0.04; p < 0.05). The full lines indicate positive effects, dotted lines indicate negative effects, the values next to the lines are the normalized pathway coefficients. ns denotes p > 0.05; * denotes p ≤ 0.05; * *denotes p ≤ 0.01; *** denotes p ≤ 0.001