COS 55-3 - Plant-soil microbe interactions are spatially structured in Elephantopus tomentosus

Abstract: Climate warming has caused plant species to shift their distributions toward higher elevations and latitudes, but it is unclear if their associated microbes will migrate at the same pace. Spatial mismatch with their microbial community could diminish plant fitness in an otherwise favorable climate if plant migration outpaces the migration of beneficial microbes; alternatively, plants could have elevated survival and establishment in their expanding geographic range if they escape host-specific pathogens. Limited work has characterized how soil microbial communities differ across space, or the extent to which plants are adapted to their local soil microbes. I collected seeds and soils from wild populations of Elephantopus tomentosus for a greenhouse inoculation experiment comparing the fitness of plants grown in their local soil microbial community with plants grown in soils from distant populations. Higher plant fitness in local soils compared to distant soils would suggest that interactions between plants and soil microbes are locally adapted. Alternatively, higher plant fitness in distant soils compared to local soils would suggest that local pathogens constrain the fitness of their host plants. These patterns will be supported by comparisons to plant fitness in sterilized control soils.

Soil communities affect plant fitness in a spatially structured way across a subset of the range of Elephantopus tomentosus, based on whether soil is from farther north or south of its home soil. There is a trade-off between total biomass and reproductive biomass in E. tomentosus when grown in non-local soils. Total plant biomass was higher for plants grown in soils sourced from further north than their home population (Chisq=17.79, df=1, p=0.00002). However, reproductive biomass was higher for plants grown in soils sourced from further south than their home population (Chisq=5.72, df=1, p=0.0168). Plant biomass in both analyses from live soils were equal to or less than biomass from the sterilized controls, suggesting that changes in pathogens are driving these patterns. This tradeoff between total and reproductive biomass may be important in perennial E. tomentosus by affecting lifetime fitness – that is, larger plants may be more likely to survive and reproduce for a second year. Longer term fitness will be investigated in future studies to understand how these results could indicate expansion potential at the leading edge of a plant’s distribution.