Deschampsia biomass, soil microbes and endophyte root colonization for snowmelt and microbial innoculation transplant experiment in the Green Lakes Valley, 2015-2018

As organisms shift their geographic distributions in response to
climate change, biotic interactions have emerged as an important
factor driving the rate and success of range expansions. Plant-microbe
interactions are an understudied but potentially important factor
governing plant range shifts. We studied the distribution and function
of microbes present in high-elevation unvegetated soils, areas that
plants are colonizing as climate warms, snow melts earlier and the
summer growing season lengthens. Using a manipulative snowpack and
microbial inoculation transplant experiment, we tested the hypothesis
that growing season length and microbial community composition
interact to control plant elevational range shifts. We predicted that
a lengthening growing season combined with dispersal to patches of
soils with more mutualistic microbes and fewer pathogenic microbes
would facilitate plant survival and growth in previously unvegetated
areas. We identified negative effects on survival of the common alpine
bunchgrass Deschampsia cespitosa in both short and long growing
seasons, suggesting an optimal growing season length for plant
survival in this system that balances time for growth with soil
moisture levels. Importantly, growing season length and microbes
interacted to affect plant survival and growth, such that microbial
community composition increased in importance in suboptimal growing
season lengths. Further, plants grown with microbes from unvegetated
soils grew as well or better than plants grown with microbes from
vegetated soils. These results suggest that the rate and spatial
extent of plant colonization of unvegetated soils in mountainous areas
experiencing climate change could depend on both growing season length
and soil microbial community composition, with microbes potentially
playing more important roles as growing seasons lengthen.