Parental effects can be transmitted through the rhizosphere microbiome

Plant responses to environmental changes, including to competition by neighboring plants, can be influenced by soil microbes. They can also be modified through parental effects, which can transmit environmental cues across generations and shape plant phenotypes through various mechanisms such as epigenetic modifications. However, we do not yet know whether parental effects in plants can also act through modifications of the rhizosphere microbiota. Here, we grew eight genotypes of Phragmites australis with or without interspecific competition, and examined its transgenerational effects on offspring phenotype and rhizosphere microbial communities in a common environment. We found that competition decreased plant growth in a genotype-specific manner, but plants whose parents had been exposed to competition previously shifted their functional phenotypes towards a more conservative resource strategy. Notably, parental competition also altered the diversity and community structure of rhizosphere soil bacteria and fungi in offspring plants, and structural equation models indicated that these soil microbiome changes may have driven some of the observed changes in offspring phenotypes. Our study demonstrates that parental environmental effects can influence offspring traits not only directly, but also through alteration of rhizosphere microorganisms, and that parental effects are more complex than we previously knew.