Tare soil alters the composition of the developing the potato rhizosphere microbiome

Understanding the factors influencing microbial community composition in the rhizosphere is an important step towards managing the microbiomes of globally important crops like potato (Solanum tuberosum). Potato is vegetatively propagated and seed tubers are planted with tare soil, or soil adhering to the tuber surface, from their field of origin. Bulk soil is known to influence rhizosphere microbiome composition, but whether tare soil additionally contributes to compositional variation is not known. We tested this hypothesis in a greenhouse experiment where tare soil was removed (or remained intact for controls) prior to planting in either soil from a potato field or soil from a previously uncultivated area next the potato field. We used ITS and 16S metabarcoding to characterize the fungal and bacterial rhizosphere communities of plants grown from the experimental seed tubers. We found that tare soil influenced rhizosphere microbial composition, more strongly for fungi than bacteria. As expected, bulk soil origin explained the greatest amount of variation in the rhizosphere microbiome overall, but we found no evidence that the impact of tare soil on microbial community composition differed between bulk soil origins. The magnitude of the tare soil effect did, however, depend in part on seed tuber origin. Our findings reveal that tare soil explains a significant, though modest, amount of variation in rhizosphere composition, and sets the stage for future work addressing functional consequences for plant health and productivity.