Does soil history decline in influencing the structure of bacterial communities ofBrassica napushost plants across different growth stages?

Abstract Soil history has been shown to condition future plant-soil microbial communities up to a year after being established. However, previous experiments have also illustrated that mature, adult plants can “re-write”, or mask, different soil histories through host plant-soil microbial community feedbacks. This leaves a knowledge gap concerning how soil history influences bacterial community structure across different growth stages. Therefore, in this experiment we tested the hypothesis that previously established soil histories will decrease in influencing the structure of Brassica napus bacterial communities over the growing season. We used an on-going agricultural field experiment to establish three different soil histories, plots of monocrop canola ( B . napus ), or rotations of wheat-canola, or pea-barley-canola. During the following season, we repeatedly sampled the surrounding bulk soil, rhizosphere and roots of B . napus at different growth stages— the initial seeding conditions, seedling, rosette, bolting, and flower— from all three soil history plots. We compared the taxonomic composition and diversity of bacterial communities, as estimated using 16S rRNA metabarcoding, to identify any changes associated with soil history and growth stages on the different B. napus soil bacterial communities. We found that soil history remained significant across each growth stage in structuring the bulk soil and rhizosphere communities, but not the roots. This suggests that the host plant’s capacity to “re-write” different soil histories may be quite limited as key components that constitute the soil history’s identity remain present and continue to impact bacterial communities. For agriculture, this highlights how previously established soil histories persist and may have important long-term consequences on future plant-microbe communities, including bacteria.