Soil properties in agricultural systems affect microbial genomic traits

Understanding the relationships between bacterial taxa, their ecological and genomic traits, and their environment, is important for elucidating the mechanisms that drive microbial community dynamics and their roles in ecosystem functioning. This is especially true for soils, where dramatic shifts in resource input or physicochemical properties occur through land use and agricultural practices. Here, we examined the relationships between soil properties and bacterial traits within highly managed agricultural soil systems subjected to arable crop rotations or management as permanent pasture. We assessed the bacterial communities within these soils using amplicon sequencing and assigned each amplicon trait scores for rRNA copy number, genome size, and GC content, which are classically associated with potential growth rates and specialisation. We also calculated the niche breadth trait of each amplicon as a measure of social ubiquity within the examined samples. Within this soil system, we demonstrated that pH was the primary driver of bacterial traits. The weighted mean trait scores of the samples revealed that bacterial communities associated with soils at lower pH (<7) tended to have larger genomes (possess more potential plasticity), have more rRNA (higher growth rate potential), and are more ubiquitous (have less niche specialisation) than the bacterial communities from higher pH soils. Our findings highlight not only the association between pH and bacterial community composition but also the importance of pH in driving community functionality by directly influencing genomic and niche traits.