Experimental setup
Topsoil (0-20 cm) was collected from a conventional agricultural field (latitude: 53.144472, longitude: 9.912944) near Lüneburg, Germany. General soil properties were as follows: soil pH: 4.9, soil organic matter content: 2.3%, total nitrogen content: 0.07%, total carbon content: 0.98%, and C to N ratio: 12:1. The soil was passed through a 2.5 mm sieve and γ-sterilized with 30 kGy (company info). To investigate the effects of soil microbiome on root traits and recruitment of species-specific bacterial communities in the rhizospheres, freshly collected field soil (five independent field replicates) with and without γ-sterilization was used as soil inoculum to introduce disturbed soil microbiome (DSM) and non-disturbed soil microbiome (NSM), respectively. For instance, the DSM inoculum had 56% lower microbial abundance than NSM as determined through microbial biomass estimation from chloroform-fumigation extraction method (Vance, Brookes & Jenkinson 1987). Only 10% of soil inoculum was mixed with 90% γ-sterilized soil that was collected from the same field as that of inoculum soil to fill the rhizoboxes. This allowed us to keep all the abiotic properties of soil in each rhizobox similar and investigate the effects of only DSM versus NSM. Seeds of modern (Hordeum vulgareL. var. Barke) and wild barley (H.spontaneum K. Koch var.spontaneum ) were surface sterilized with 70% ethanol and thoroughly rinsed with distilled water. Seeds were de-husked to facilitate germination for wild barley. Thereafter, seeds were soaked in distilled water overnight before transferring to petri-plates having sterilized moistened filter paper and allowed to germinate in a climate chamber. After germination (within 2 days), seedlings were transferred to rhizoboxes (one seedling per rhizobox). Each rhizobox (58.0 x 26.6 x 2.0 cm3) contained a transparent window to non-destructively and dynamically monitor root development. Rhizoboxes were positioned at 45-50° angle from the table surface in the climate chamber that facilitated roots to grow towards the transparent window which helped in their visualization. The environmental conditions inside the climate chamber were kept constant and were as follows: light phase: 21.6 ± 1.1 °C; dark phase: 17.2 ± 1.0 °C; 16 hr light/8 hr dark; lamps: SANlight P4-serie, 400–760 nm; PAR: 302 ± 21 μmol m−2s−1. In total, the experiment consisted of two barley species (modern and wild barley) times two type of soil inocula (disturbed versus non-disturbed) times five replicates of each treatment combination, giving us 20 experimental units.