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.