# Impact of Fertilisation on the Bacterial Core Microbiome of Grassland Soils: Abundance in the Field and Growth In Vitro

## TL;DR

This study shows how different fertilization methods, especially pig slurry, affect the bacterial makeup of grassland soil and how these effects can be studied in lab experiments.

## Contribution

The study demonstrates that culturable soil bacteria can be used to replicate field observations in controlled lab settings under different fertilization regimes.

## Key findings

- Pig slurry fertilization caused the most significant changes in the bacterial core microbiome composition.
- Bradyrhizobium japonicum growth was inhibited by pig slurry, while Nocardioides albus and Solirubrobacter pauli grew better in its presence.
- Culturable bacteria mirrored field abundance patterns in in vitro experiments, validating lab-based microbiome studies.

## Abstract

Anthropogenic activities may have profound impacts on the soil microbiome with consequences for soil health, agriculture and food production. Here, we investigated the impact of different fertilisation regimes on the composition of the bacterial soil microbiome in grassland ecosystems by 16S rRNA gene amplicon sequencing and in vitro growth experiments with culturable representatives of the bacterial core microbiota. We observed a large proportion of taxa shared across fertilisation regimes without significant differences in their evenness, but shifts in the composition of the bacterial core microbiome by fertilisation. These effects were most pronounced for fertilisation with pig slurry (PS). Analysis of microbiome multivariable association with linear models identified bacterial biomarker taxa for different fertilisation regimes. This enabled the selection of several culturable representatives for in vitro growth experiments. Consistent with the relative abundances of Bradyrhizobium, Nocardioides, and Solirubrobacter in field samples, the growth of
Bradyrhizobium japonicum
was inhibited by PS, while
Nocardioides albus
and
Solirubrobacter pauli
exhibited enhanced growth in its presence. Our results suggest that culturable representatives of the bacterial core soil microbiota can be identified and used to investigate the effects of specific parameters linked to anthropogenic impacts under controlled laboratory conditions.

Effects of different organic fertilisation regimes on the bacterial microbiome of grassland soil were analysed by 16S rRNA amplicon sequencing. Different fertilisation regimes led to distinct changes in the composition of the bacterial microbiome and effects were most pronounced when soil was fertilised with pig slurry. In in vitro growth experiments, the response of culturable representatives of the bacterial core microbiome to pig slurry mirrored their changes in abundances in the field.