New Phytolog. http://doi.org/xmn (2014)

That the community of microbes associated with an organism affects its physiology is well established. But the distance over which these effects extend is underappreciated.

Studying lignin production in barley, Alison Bennett, of the James Hutton Institute, UK, and colleagues found that the soil microbiome has a stronger effect above ground than below it. They grew wild-type barley plants, and mutants impaired in their ability to synthesize lignin, on soils inoculated with two different microbial communities — one from a fertile agricultural land, the other from a nutrient-poor sand dune. Comparisons across the resulting eighteen treatments — six plant types and three soils, including sterile soil — found no effect of the plants grown on their colonization by soil microbes. However, the soil microbiome explained 6% of the lignin variation in roots and 21% of the variation in shoots, the most statistically significant effect the researchers detected.

Adjusting the properties of plants by grafting onto different rootstocks is commonplace; Bennett et al. have shown what is living on the roots deserves as much consideration as the roots themselves.