Patterns of microbiome-mediated plant-soil feedback intensity in organic versus conventional farm soils

Plants influence soil properties, impacting subsequent growth via plant-soil feedback (PSF). We collected rhizosphere soils from common ragweed ( Ambrosia artemisiifolia) across 24 organic and conventional farms to create microbial inoculants. The inoculants were used to condition soils in greenhouse pots that were re-planted with new seedlings to simulate a PSF cycle. We observed negative PSF in 21 out of 24 farming system treatments. However, more intense PSF effects were observed in systems with microbiomes derived from conventional farm soils. Higher soil bacterial diversity was correlated with less negative PSF in systems with microbiomes from organic farm soils. Most of the plant growth-suppressive microbiomes were derived from conventional farms, whereas microbiomes that had weakly negative, neutral, or positive effects on plant growth originated largely from organic farm soils. Network analysis revealed distinctly different bacterial interactions between samples with high versus low PSF, as well as between organic and conventional farm soils. Our findings suggest that field management practices structure the rhizosphere microbiome of A. artemisiifolia , potentially allowing the bacterial microbiome to intensify plant-soil feedback. Microbiome properties, like microbial diversity, could play a role in influencing the trajectory of these feedback processes.