As climates change, tree species will need to either shift in space to track historic climates or adapt or acclimate to novel climate conditions in place. We are exploring a third option: can tree seedlings expand their climate tolerance by altering the microbial associates of their roots? Using a combination of experiments in field and greenhouse conditions, we tested whether pre-inoculating tree seedlings of a variety of species with microbes sourced from sites along climatic gradients can alter seedling growth and survival. We collected live soil from six locations in Wisconsin and six in Illinois, and grew tree seedlings of 10 species with these soils for eight weeks in greenhouse conditions. We then planted the seedlings inoculated with soil from Wisconsin sites into a forest in northern Wisconsin, and the seedlings inoculated with soil from Illinois sites into a forest in central Illinois, in ambient or rainfall reduced plots. We have followed survival for three growing seasons to ask:
- Does inoculation with microbes foreign to the field site increase or decrease seedling survival in ambient conditions?
- Does inoculation with microbes sourced from hotter or drier locations increase seedling survival in rainfall reduced conditions?
Results/Conclusions
Over two growing seasons at two sites (in central Illinois and northern Wisconsin), we have found that even when planted into field sites with intact indigenous microbial communities, seedling survival depended in part on the microbial inoculation they received prior to planting. However, the microbial inoculation effect different between the two sites. In the northern Wisconsin site, survival was always highest with the local microbial source. This effect appeared to manifest primarily in over-wintering survival of seedlings. This phenomenon mirrors the “local is best” approach to restoration genetics, in which locally sourced seeds tend to out-perform seeds from more distant populations due to local adaptation.
Contrastingly, in our hotter and drier site in central Illinois, seedling survival was similar across microbial inoculum sources in the ambient conditions, but survival was significantly increased in the rainfall reduced treatments when seedling were pre-inoculated with microbes from more southern (hotter and more arid) sites. This effect suggests that microbial communities assembled under hot and dry climatic conditions may contain taxa that can impart greater drought tolerance to host plants.