With the intensification of desertification in northwest China, drought has become a serious environmental problem restricting plant growth and ecological restoration. Recently, dark septate endophytes (DSEs) have attracted more attention because of their ability to improve plants’ resistance to drought. Here, we investigated DSE colonization and species diversity in roots of Lycium ruthenicum collected from Anxi and Minqin, in northwest China, during July, September, and December 2019. This study aimed to evaluate the influence of seasonality and sampling sites on DSEs. In different seasons, DSE colonization varied with the phenology of L. ruthenicum. At different sites, DSE colonization significantly differed. Four isolates were reported in desert ecosystems for the first time. The results showed microsclerotial colonization was directly affected by changing seasons, while hyphal colonization and species diversity were directly affected by sampling sites. The soil organic carbon, pH, alkaline phosphatase, and alkali-hydrolyzable nitrogen were the main predictors of DSE colonization and species diversity. We conclude that DSE colonization and diversity showed significant spatial–temporal heterogeneity and were closely related to soil factors. This research provides a basis for the further understanding of the ecological functions of DSEs and their application potential for vegetative restoration and agricultural cultivation in drylands.

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.

Dark septate endophytes (DSE) may facilitate plant growth and stress tolerance in stressful ecosystems. However, little is known about the response of medicinal plants to DSE, especially under heavy metal stress. This study aimed to investigate how DSE affects the growth of Dendranthema morifolium in medicinal plants under cadmium (Cd) stress. In this investigation, the sterile and non-sterile inoculations were carried out to evaluate the effect of three DSE strains on D. morifolium stressed with Cd. For the root, DSE15 sterile or non-sterile inoculation resulted in enhanced root biomass, root volume, the Cd content of roots, and the indoleacetic acid (IAA) levels in D. morifolium under Cd stress. DSE7 non-sterile inoculation significantly enhanced the Cd content of roots at 1 and 5 mg Cd/kg soil. Regarding impact stems and leaves, under sterile conditions, DSE7 and DSE15 effectively regulated the shoot biomass, plant height, chlorophyll level, and superoxide dismutase (SOD) content. Under sterile conditions, DSE15 positively influenced shoot biomass and plant height, while DSE7 had no significant effect on them when subjected to Cd stress. For effects on flowers under non-sterile conditions, DSE7 and DSE15 significantly increased the flower biomass under Cd stress, while DSE7 reduced the Cd transfer coefficient of flowers at 1 and 5 mg Cd/kg soil. Importantly, at 1 mg Cd/kg soil, DSE7 and DSE15 non-sterile inoculations promoted the 1, 5-dicaffeoylquinic acid content by 18.29% and 21.70%. The interaction between DSE and soil factors revealed that DSE species had significant effects on soil organic carbon and available nitrogen in D. morifolium non-sterile soil. The DSE15 inoculation enhanced soil organic carbon content, while the inoculation of DSE7 and DSE15 reduced soil available nitrogen content under Cd stress. These results contribute to a better understanding of DSE-plant interactions in habitats contaminated by heavy metals and demonstrate the potential utility of DSE strains for cultivating medicinal plants.