COS 230-5 - Plant-soil feedbacks hinder mountain species' range expansions

Abstract: As climate change accelerates, plant species must either become locally extirpated or shift their ranges to stay within their species’ range of tolerance to climatic variables. However, plant species vary in their ability to shift ranges, depending on dispersal traits, their relationship with chemical and physical soil properties, and the way in which they interact with soil organisms. For example, plant interactions with soil enemies or soil mutualists at the invasion front can either promote or hinder range expansion.

Herein we test soil processes associated with plant range expansion at two mountain sites using elevation as a proxy for the invasion front of six native range-expanding species. For each of two regions (Norway, Switzerland), we selected range-expanding plant species from within three functional groups (graminoid, forb, and legume). We compared plant growth on sterilized soils and unsterilized soils to growth on soil inoculated with biota sourced from 1) within the range of the species or 2) beyond the range of the species. This design allows us to test whether release from soil enemies, enhanced interactions with soil mutualists, or impaired interactions with soil mutualists impacted native plant range expansions. In addition, we replicated the experiment with five degrees of warming to project how climate change might impact plant-soil feedbacks and future range expansions. Results are paired with bacterial and fungal sequencing data to confirm mechanisms of native plant range expansions. In addition, results are compared with field observations of the same species’ growths in community contexts under ambient and warmed conditions.

Broadly, we found no evidence for enemy release or enhanced interactions with soil mutualists across our two sites and six species. One species showed strong evidence for impaired interactions with soil mutualists at high elevation compared to low elevation. Another species showed comparable interactions with soil biota across high and low sites. The remaining four species all showed reduced growth the more high-elevation a soil became, suggesting that for these species both soil biotic and soil abiotic factors hinder mountain plant range expansions.