| Summary: | Plant-associated bacterial assemblages are critical for plant fitness. Thus, identifying a consistent plant-associated core microbiome is important for predicting community responses to environmental changes. Our target was to identify the core bacterial microbiome of orchard grass <i>Dactylis glomerata</i> L. and to assess the part that is most sensitive to land management. <i>Dactylis glomerata</i> L. samples were collected from grassland sites with contrasting land use intensities but comparable soil properties at three different timepoints. To assess the plant-associated bacterial community structure in the compartments rhizosphere, bulk soil and endosphere, a molecular barcoding approach based on high throughput 16S rRNA amplicon sequencing was used. A distinct composition of plant-associated core bacterial communities independent of land use intensity was identified. <i>Pseudomonas</i>, <i>Rhizobium</i> and <i>Bradyrhizobium</i> were ubiquitously found in the root bacterial core microbiome. In the rhizosphere, the majority of assigned genera were <i>Rhodoplanes</i>, <i>Methylibium</i>, <i>Kaistobacter</i> and <i>Bradyrhizobium</i>. Due to the frequent occurrence of plant-promoting abilities in the genera found in the plant-associated core bacterial communities, our study helps to identify “healthy” plant-associated bacterial core communities. The variable part of the plant-associated microbiome, represented by the fluctuation of taxa at the different sampling timepoints, was increased under low land use intensity. This higher compositional variation in samples from plots with low land use intensity indicates a more selective recruitment of bacteria with traits required at different timepoints of plant development compared to samples from plots with high land use intensity.
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