Will parallel or mismatched migration of plants and microbial communities accelerate or impede range shifts and gene flow in response to climate change?

Background/Question/Methods

Tree species and population ranges are predicted to shift in latitude and elevation as climates change. These predictions are based on primarily on correlations between current distributions and climates, and evidence of past range shifts. However, species ranges may also be determined by biotic and abiotic conditions unrelated to climate. We asked whether the soils and microbial communities tree populations will encounter as they shift poleward are likely to facilitate or impede this shift, using two common eastern tree species (Carpinus caroliniana and Juglans nigra). As we know little about how microbial taxa will respond geographically to climate change, we tested how simulated microbial migration would affect tree seedlings, either alone or in concert with simulated plant population migration. We performed a greenhouse experiment in which tree populations, soil microbial communities, and abiotic soil conditions from four latitudinal were used to simulate four migration scenarios: 1) status quo, 2) tree migration only: tree populations moved one latitudinal step north with respect to soils and microbes, 3) microbial migration only: microbial inocula moved one step north with respect to soils and tree populations, and 4) co-migration: both tree populations and microbial inocula shifted together into soils from one step north.

Results/Conclusions

Tree seedling growth responded in idiosyncratic ways to the shift in soil and microbial contexts.  Plants often perfomed best when shift way from their historical microbial community, may reflect escape from co-evolved pathogens. However, the abiotic soil context altered this outcome in many cases. Future work will examine microbial community composition in these soils and nutrient and water status of the experimental plants to provide more mechanistic understanding of these effects. These results suggest that understanding the non-climatic factors affecting tree establishment and growth can potentially improve our ability to predict range shifts and gene flow in response to changing climates.