The Age of Absorptive Roots Impacts Root-Adjacent Microbial Composition in Grapevines

In grapevine, metabolic activity of absorptive roots changes rapidly as roots age but it is unclear whether nearby microbial assemblages shift as well. Here, we investigated whether first-order root age affects bacterial and fungal variation adjacent to the root surface, and whether root age should be integrated into future studies on root functional traits and associated microbes. We hypothesized that microbial diversity and composition would differ between young (<= 11 days old) and old (11.5 to 40 days old) first-order roots due to expected differences in metabolism over the root lifespan (i.e., higher metabolism in young roots). Overall, we found that microbial composition was distinct between young and old absorptive roots, with stronger evidence at the phylum and amplicon sequence variant (ASV) taxonomic levels for fungi (P = 0.003 and P = 0.038, respectively) than bacteria (P = 0.082 and P = 0.129, respectively). Furthermore, we identified differentially abundant fungal and bacterial ASVs in young and old roots that related to expected differences in root function, including instances of microbes previously described as copiotrophs more abundant adjacent to young roots and microbes described as oligotrophs and saprotrophs more abundant adjacent to old roots. In contrast to the distinct shifts in microbial composition, there was little evidence of shifts in alpha diversity (i.e., observed ASVs and Shannon diversity) between young and old roots. Our study suggests that future work on the impacts of root functional traits on localized microbial composition may improve results interpretation and reduce some variation by accounting for root age at sampling.