Plant developmental stage, rather than inoculation with Hartmannibacter diazotrophicus, determines the composition of the bacterial, fungal, and protist microbiome in winter wheat

The application of plant growth-promoting rhizobacteria (PGPR) for inoculation of seeds, soils, and plants is becoming increasingly important due to the environmental impact of extensive use of chemical treatments in plant production. In this study, we investigated the effects of seed inoculation with Hartmannibacter diazotrophicus E19 on the bacterial, fungal and protist (Cercozoa) microbiome of winter wheat. The results showed that the inoculation of H. diazotrophicus E19 had no significant effect on the microbiome of roots, rhizosphere and in the bulk soil of winter wheat. Instead, the composition of the winter wheat microbiome appears to be more influenced by plant developmental stage and sampling material. Inoculation resulted only in minor effects, reflected by a limited number of ASVs showing positive or negative differential abundance compared to the controls like Chryseolinea , Symbiobacterium , Malbranchea , Hormiactis and Sandonidae. These findings confirm that the microbiome composition of winter wheat undergoes only minimal changes upon inoculation with H. diazotrophicus E19. • Field study on impact of H. diazotrophicus E19 seed inoculation. • H. diazotrophicus E19 inoculation had no significant impact on wheat microbiome. • Especially Cercozoa communities were also unaffected by the inoculation. • The microbiome is shaped by the sample type and sampling time. • Individual ASVs were still affected by inoculation.