Mycorrhizal symbiosis alleviates plant water deficit within and across plant generations via plasticity

Phenotypic plasticity is essential for organisms to adapt to local ecological conditions. It is expected that mutualistic interactions, such as arbuscular mycorrhizal (AM) symbiosis, mediate plant phenotypic plasticity, although it is not clear to what extent this plasticity may be heritable (i.e., transgenerational plasticity). We tested for plant plasticity within- and across-generations in response to AM symbiosis and varying water availability in a full factorial experiment over two generations, using a genetically uniform line of a perennial apomictic herb, Taraxacum brevicorniculatum . We examined changes in phenotype, performance, and AM fungal colonization of the offspring throughout plant development. AM symbiosis and water availability triggered phenotypic changes during the life cycle of plants. Additionally, both triggered adaptive transgenerational effects, especially detectable during the juvenile stage of the offspring. Water deficit and absence of AM fungi caused concordant plant phenotypic modifications towards a “stress-coping phenotype”, both within- and across-generations. AM fungal colonization of offspring was also affected by the parental environment. AM symbiosis can trigger within-generation and transgenerational plasticity in terms of functional traits related to resource-use acquisition and AM fungal colonization. Thus, transgenerational effects of mycorrhizal symbiosis are not limited to plant fitness, but also improve plants’ ability to cope with environmental stress.