Dynamic plant-soil microbe interactions: the neglected effect of soil conditioning time.

Plant-soil feedback (PSF) may change in strength over the life of plant individuals as plants continue to modify the soil microbial community. However, the temporal variation in PSF is rarely quantified and its impacts on plant communities remain unknown. Using a chronosequence reconstructed from annual aerial photographs of a coastal dune ecosystem, we characterized > 20-yr changes in soil microbial communities associated with individuals of the four dominant perennial species, one legume and three nonlegume. We also quantified the effects of soil biota on conspecific and heterospecific seedling performance in a glasshouse experiment that preserved soil properties of these individual plants. Additionally, we used a general individual-based model to explore the potential consequences of temporally varying PSF on plant community assembly. In all plant species, microbial communities changed with plant age. However, responses of plants to the turnover in microbial composition depended on the identity of the seedling species: only the soil biota effect experienced by the nonlegume species became increasingly negative with longer soil conditioning. Model simulation suggested that temporal changes in PSF could affect the transient dynamics of plant community assembly. These results suggest that temporal variation in PSF over the life of individual plants should be considered to understand how PSF structures plant communities.