Colonization by dark septate endophytes improves the growth and rhizosphere soil microbiome of licorice plants under different water treatments

Abstract

Dark septate endophytes (DSE) are facultative biotrophic ascomycetes that colonize plant roots. DSE may provide nutrients to their plant hosts and help them adapt to various abiotic and biotic stresses. However, their effects on the microbiome composition in plant rhizosphere need further clarification. Here, we conducted a pot experiment to establish whether the responses of licorice (Glycyrrhiza uralensis) to DSE (Acrocalymma vagum, Paraboeremia putaminum) inoculation under different water treatments are caused by changes in the rhizosphere microbiome. Rhizosphere microbiome compositions were measured by Illumina MiSeq sequencing of the 16S and ITS2 rRNA genes. The inoculation with DSE strains had a positive effect on plant growth of licorice depending on DSE species and water treatments. Subsequently, a total of 1278 fungal and 1583 bacterial operational taxonomic units (OUTs) were obtained at a 97% sequence similarity level. Ascomycota were the predominant fungi and Proteobacteria, Actinobacteria, Chloroflexi and Firmicutes were the predominant bacteria. DSE inoculation and water regime significantly influenced the microbiome composition. However, the effects of DSE on the fungal community were greater than those on the bacterial community. P. putaminum exerted a stronger impact on the licorice rhizosphere microbiome than A. vagum under drought stress. The observed changes in edaphic factors (water condition, soil organic matter, available nitrogen, available phosphorus, and available potassium) caused by DSE inoculation could be explained by the variations in microbiome composition. A network analysis indicated that DSE inoculation augmented the relative abundance of beneficial symbiotrophic fungi and growth-promoting bacteria but diminished the relative abundance of pathogens in the licorice rhizosphere. The present study showed that the licorice rhizosphere microbial community differed between the DSE-inoculated and uninoculated plants. DSE had a stronger influence on the fungal than on the bacterial rhizosphere community under drought stress. These give us the guidance to develop biofertilizers with DSE consortia to enhance the cultivation of medicinal plants by shaping soil microbial community structure and soil nutrient status in dryland agriculture.