Species interactions can either promote or hinder the ability of a species to track climate change. Despite the well-known and ubiquitous importance of soil microbes to plant fitness, the role of plant-microbe interactions in plant range shifts has rarely been studied or included in predictive models. We hypothesized that earlier snowmelt due to climate change would enable plant establishment in unvegetated areas, but that establishment would also depend on the microbial communities in the unvegetated soil. Prior work shows that mutualistic microbes are present but patchily distributed in unvegetated soil. We grew three alpine plant species in different soil inocula collected at various locations across a high-alpine, talus-field ecosystem, including from unvegetated and vegetated soils, to encompass a variety of microbial communities. After growing plants in the greenhouse with these inocula to establish particular sets of plant-microbe interactions, we then transplanted the plants into high elevation unvegetated soils. We also manipulated the growing season in half of the plots by applying a thin layer of black sand onto the snow surface at peak snowpack, which accelerated snowmelt and extended the growing season by one week.
Results/Conclusions
In the greenhouse, growth of Deschampsia cespitosa and Oxyria digyna were significantly affected by soil inoculum. Sequencing of roots and soils showed that each inoculum created a unique microbial community in the rhizosphere soil and within the plant roots. After the first growing season in the field, growth of Deschampsia was significantly affected by the different soil inoculum treatments. Growth was the greatest in two inocula from vegetated soils, and one inoculum from unvegetated soil. There was no effect of the extended growing season length treatment in the first season of the experiment. Oxyria and Silene acaulis both experienced high levels of mortality in all growing season and microbial treatments. These results suggest that some, but not all, unvegetated soils contain microbial communities that facilitate plant growth. This could affect the rate or spatial extent of plant movement uphill into unvegetated soils as climate warms and snow melts earlier.