Plant lignin content altered by soil microbial community

Summary Questions have been raised in various fields of research about the consequences of plants with modified lignin production. As a result of their roles in nutrient cycling and plant diversity, plant–soil interactions should be a major focus of ecological studies on lignin‐modified plants. However, most studies have been decomposition studies conducted in a single soil or in sterile soil. Thus, we understand little about plant–soil interactions in living lignin‐modified plants. In lignin mutants of three different barley ( Hordeum vulgare ) cultivars and their corresponding wild‐types associated with three different soil microbial communities, we asked: do plant–soil microbiome interactions influence the lignin content of plants?; does a mutation in lignin production alter the outcome of plant–soil microbiome interactions?; does the outcome of plant–soil microbiome interactions depend on host genotype or the presence of a mutation altering lignin production? In roots, the soil community explained 6% of the variation in lignin content, but, in shoots, the soil community explained 21% of the variation in lignin content and was the only factor influencing lignin content. Neither genotype nor mutations in lignin production explained associations with fungi. Lignin content changes in response to a plant's soil microbial community, and may be a defensive response to particular components of the soil community.