Plant Growth and Soil Microbial Impacts of Enhancing Licorice With Inoculating Dark Septate Endophytes Under Drought Stress

Abstract

This study mainly aimed to investigate the effects of dark septate endophytes (DSE) (Acrocalymma vagum, Paraboeremia putaminum, and Fusarium acuminatum) on the growth and microbial community composition in the rhizosphere soil of a medicinal plant, licorice (Glycyrrhiza uralensis), grown in the non-sterile soil under drought stress. The results showed that three DSE strains could effectively colonize the plant roots and form a strain-dependent symbiosis with licorice. Although drought stress declined the growth of licorice plants, these decreases were partly recovered by DSE inoculation. Specifically, the inoculation of A. vagum and P. putaminum significantly increased the biomass and glycyrrhizin content, whereas A. vagum and F. acuminatum increased glycyrrhizic acid content of host plants under drought stress. However, the inoculation of F. acuminatum showed significant negative effects on the shoot, root, and total biomass of licorice plants. In addition, the effects of DSE inoculation on the morphological, photosynthetic, and antioxidant parameters of licorice plants, and mineral nutrient and microbial community composition in the rhizosphere soil were dependent on the DSE species as well as water regime. Interestingly, DSE inoculation significantly increased AM fungi content under drought stress. In addition, DSE associated with water had a significant positive influence on soil organic matter, available phosphorus (P), AM fungi, leaf number, soluble protein, SOD activity, total root length, root branch, and glycyrrhizic acid content. Based on the results of variance partitioning analysis, 17.0, 34.0, 14.9, 40.1, 28.2, and 18.0% variations in shoot morphology, root morphology, plant biomass, active ingredient, photosynthetic parameters, and antioxidant parameters, respectively, were attributable to the presence of certain soil microorganisms. These findings suggest the possibility that DSE inoculation improved the root development and nutrient absorption of host plants, altered the soil microbiota, and might also contribute to plant growth and survival under drought conditions. As A. vagum exhibited positive effects on the plant biomass, morphological and physiological parameters, and active ingredient content in licorice plants under drought stress, it was considered to be the best fungus for licorice cultivation. These results contribute to the understanding of the ecological function of DSE fungi in dryland agriculture.

Variation of soil microbiome in licorice rhizosphere driven with inoculating dark septate endophytes under drought stress

“…It was unknown whether DSE-mediated changes in the rhizosphere microbial communities augment drought stress tolerance in licorice. Our previous study showed that DSE inoculation (A. vagum and P. putaminum) improve licorice growth and survival under drought conditions [8]. In the present study, a network structure analysis disclosed that both soil fungal and bacterial networks were characterized by high specialization and modularity.…”

“…Biotic and abiotic stressors alter rhizosphere microbe community structure and may augment or diminish certain microbial populations [32,33]. He et al [8] found that interactions between DSE inoculation and water regime markedly in uenced the soil organic matter content. Compared to the uninoculated condition, A. vagum inoculation under drought conditions increased soil available N and P. In contrast, P. putaminum inoculation decreased soil organic matter and available N relative to the uninoculated condition.…”

“…In its natural habitats, the licorice rhizosphere harbors actinobacteria, rhizobia, other soil bacteria, AM, and DSE with plant growth-promoting activity [23,24]. An ester-linked phospholipid fatty acid (PLFA) analysis in our previous study showed that DSE (Acrocalymma vagum and Paraboeremia putaminum) inoculation increased AM and gram-negative bacterial abundance in the licorice rhizosphere under drought stress [8]. However, its effects on the composition of the microbial communities in the licorice rhizosphere remain unclear.…”

“…Several studies have shown that plant adaptation to abiotic stress is closely associated with rhizosphere microorganisms [6,7]. Bene cial endophytic fungal colonization can alter root growth, increase plant biomass, reduce water loss, and help host plants adapt to arid environments [8,9]. Moreover, dark septate endophytes (DSE) enhance viral resistance and heavy metal tolerance in plants [10,11].…”

“…They are integral and functional parts of plant roots [12]. DSE inoculation facilitates plant growth, nutrient uptake, and biotic and abiotic stress tolerance [8,11]. Previous studies demonstrated that rhizosphere-associated microbes indirectly affect plant growth by changing the rhizosphere microbial community composition and activity.…”