PS 4-55 - Determining the spatial extent of plant soil feedbacks between two foundational desert species

Abstract: As climate conditions change and species are forced to adapt to their environment or move, it is important to understand the mechanisms that inhibit or promote species range limits and expansion. For sessile organisms such as plants, plant soil feedbacks (PSFs) are one potential mechanism that determines how well a plant will survive within or outside of its existing range. At the Sevilleta National Wildlife Refuge in New Mexico, there is a transition from the Chihuahuan Desert Shrubland ecosystem in the south to Chihuahuan Desert Grassland ecosystem in the north. At this ecotone, vegetation is dominated by Bouteloua eriopoda (black grama), a perennial grass, and Larrea tridentata (creosote), a perennial shrub. Range dynamics at the ecotone between these species have been stable for the past 10 years, but creosote cover has increased while black grama cover has decreased. Currently, there are no abiotic factors that prevent a “woody takeover” by creosote into grasslands. However, there are distinct fungal communities associated with grassland, ecotone, and shrubland soils that would likely influence the success or failure of creosote range expansion. Our work aims to understand the spatial extent to which microbes influence PSF of and between two foundational species in a desert ecotone. This will allow us to better predict changes in grass-shrub range dynamics in the Chihuahuan Desert as well as other drylands, which account for 40% of global ecosystems.



To determine the spatial extent of PSFs of black grama and creosote, we located 10 “resident plants” of each species in the ecotone and collected soil at 5 increasing distances from the base of the resident plant as inocula. We then used these field inocula in a classic pairwise plant-soil feedback greenhouse experiment. We found that while distance had no effect on black grama biomass, it had a significant effect on creosote biomass (p=0.028). Post hoc analysis revealed a significant contrast in creosote biomass between distance 2 than at distance 4 (p=0.0254); creosote performed better in closer proximity to a conspecific resident plant. In contrast, while not statistically significant, black grama trends suggested that it performed worse in close proximity to a conspecific resident plant.