Drought is a major abiotic stress factor affecting plant growth and production, while utilizing beneficial endophytic fungi is one of the most promising strategies for enhancing plant growth and drought tolerance. In the current study, a pot experiment was conducted to investigate the beneficial effects of dark septate endophyte (DSE) (Macrophomina pseudophaseolina, Paraphoma radicina) and Trichoderma (Trichoderma afroharzianum, Trichoderma longibrachiatum) inoculum on Astragalus mongholicus grown in sterile soil under drought stress, alone, or in combination. The addition of Trichoderma enhanced the DSE colonization in roots regardless of the water condition. Under well-watered conditions, M. pseudophaseolina inoculation significantly enhanced the biomass and root length of A. mongholicus. The two DSE and Trichoderma inoculum significantly improved calycosin-7-O-β-D-glucoside content. However, M. pseudophaseolina + T. afroharzianum inoculation better promoted root growth, whereas co-inoculation had higher active ingredient contents compared with single inoculation, except for P. radicina + T. afroharzianum. Under drought stress, DSE and Trichoderma inoculum significantly improved root biomass, root length, calycosin-7-O-β-D-glucoside content, and activities of nitrate reductase and soil urease. P. radicina + T. afroharzianum and P. radicina + T. longibrachiatum better increased root length, and all combinations of DSE and Trichoderma had a greater impact on the increase in formononetin content compared with the single treatments. Additionally, Trichoderma relies on antioxidant enzymes, growth hormones, and the redox system (ascorbic acid–glutathione) to resist drought, while DSE strains have an additional osmotic regulation system in addition to the drought resistance function possessed by Trichoderma, and the effect of co-inoculation (especially M. pseudophaseolina + T. longibrachiatum and P. radicina + T. afroharzianum) on plant physiological parameters was greater than that of single inoculation. This study provides a new research direction for the effects of DSE and Trichoderma on medicinal plant cultivated in dryland.

Dark septate endophytes (DSE) commonly inhabit the root systems of plants that flourish in heavy metal-contaminated soils. Nevertheless, there is limited understanding regarding the overall response of medicinal plants to DSE under heavy metal stress. The present study utilized a non-sterile pot experiment to evaluate the beneficial impacts of DSE (Paraphoma chlamydocopiosa, Paraboeremia selaginellae, and Paraphoma radicina) inoculation on Astragalus mongholicus under cadmium (Cd) stress. At 0 mg Cd/kg soil, inoculation with DSE led to a significant increase in the total biomass of the host plant by up to 34.0%. Although plant biomass decreased at 5 mg Cd/kg soil and 10 mg Cd/kg soil, the total biomass of the host plant increased by up to 72.3% after DSE inoculation. The plant height, branch number, soil and plant analyzer development (SPAD) value, and biomass were not affected by Cd concentration after inoculation with P. chlamydocopiosa and P. selaginellae. DSE emerged as the most prominent explanatory variable (44.2%) for plant growth at 10 mg Cd/kg soil. Inoculation with P. chlamydocopiosa increased root length by 47.9% and root biomass by 74.1%, and inoculation with P. chlamydocopiosa and P. selaginellae increased the indole-3-acetic acid (IAA) content by 103.6% and 105.8%, respectively, at 10 mg Cd/kg soil. Additionally, P. radicina inoculation was preferred to increase the content of calycosin-7-O-glucoside, while P. chlamydocopiosa increased the content of formononetin. DSE enhanced the accumulation of Cd in the shoot, whereas P. radicina exhibited an inhibitory effect on Cd accumulation in the root system. P. chlamydocopiosa decreased the Cd translocation factor, while P. radicina increased the Cd translocation factor, which exceeded one. The interaction between DSE and soil factors significantly contributed to the host plant growth. DSE inoculation improved soil organic carbon content and inoculation with P. chlamydocopiosa, and P. selaginellae reduced available nitrogen content, regardless of the Cd stress. DSE inoculation reduced available phosphorus content at 10 mg Cd/kg soil. Importantly, P. radicina promote the performance and calycosin-7-O-glucoside accumulation of the host plant, and reduced Cd content in the roots at 5 mg Cd/kg soil. These data enhanced comprehension of the ecological function of DSE in heavy metal-contaminated soils and demonstrated the potential utility of DSE strains for cultivating medicinal plants.

Arbuscular mycorrhizal fungi (AMF) act as intermediaries between the root systems of host plants and the surrounding soil, offering various benefits to medicinal plants, such as promoting growth and enhancing quality. However, the host range of AMF in medicinal plants and the characteristics of plant–AMF networks in farmland ecosystems remain insufficiently studied. In the present study, we measured AMF colonization, species diversity, and soil properties of 31 medicinal plants at the Anguo Medicine Planting Base in Northwest China. The medicinal plant–AMF network was subsequently analyzed, and the growth-promoting effects of AMF on Astragalus mongholicus were examined. Spore density, species richness, and total colonization exhibited significant variation across different medicinal plant species. Glomus melanosporum, G. claroideum, and Septoglomus constrictum were the dominant species among 61 AMF species. Soil organic matter, phosphatase, available nitrogen, and glomalin-related soil proteins (GRSPs) were the main factors affecting the AMF composition. Structural equation models and a variation partitioning analysis suggested a highly plant species-specific pattern of AMF distribution patterns, where the host identities explained 61.4% of changes in spore density and 48.2% of AMF colonization. The soil nutrient availability and phosphatase activity also influenced AMF colonization. Our results confirmed glomalin as an important contributor to the soil carbon in farmland for cultivating medicinal plants. The medicinal plant–AMF symbiotic network exhibited highly nested patterns, a low specialized structure, high connectance, and low modularity, which suggested saturated AMF colonization and symbiosis stability provided by redundant plant–AMF associations. Despite the wide host range among medicinal plants, AMF inoculation revealed species-specific effects on the growth performance and active ingredient content levels in A. mongholicus, G. claroideum and Sep. constrictum induced the highest biomass and active ingredient content accumulation in A. mongholicus. These findings advance our understanding of AMF community dynamics in the rhizosphere of medicinal plants and offer valuable insights for optimizing medicinal plant cultivation practices.