Analogous to the spread of non-native species, shifts in native species’ ranges resulting from climate and land use change are also creating new combinations of species in many ecosystems. These native range shifts may be facilitated by some of the same mechanisms that provide advantages for non-native species, such as enemy release, and may also have comparable impacts on the ecosystems they invade. Soil biota, in particular bacteria and fungi, are important regulators of plant community composition and belowground ecosystem function. Compared to non-native plant invasions, there have been relatively few studies examining how soil biota influence—or are influenced by—native species range expansion. We examine how a native range-expanding sagebrush species (Artemisia rothrockii) affects belowground abiotic conditions and microbial community structure and function using next-generation sequencing, and other traditional soil analyses. We utilized a range-expansion gradient, together with a shrub removal experiment and structural equation models, to determine the direct and indirect drivers of these interconnected processes.
Sagebrush colonization increased microbial richness and diversity and altered community composition across the expansion gradient. Soil organic C, N, and soil moisture increased with sagebrush presence, however results varied by elevation. We found no relationship between sagebrush and soil pH, however pH strongly influenced microbial richness, diversity, and microbial functional group relative abundances. Microbial (substrate induced) respiration was influenced by soil organic C, N, and soil moisture, as well as microbial richness and functional group relative abundances, highlighting direct and indirect effects of sagebrush on microbial community structure and function. Microbial community composition of soils after 4 years of sagebrush removal was more similar to communities in shrub interspaces than underneath shrubs, suggesting strong microbial community resilience. Our results suggest that native range expansions can have important impacts on soil biological communities, soil chemistry, and hydrology which can further impact belowground ecosystem processes such as nutrient cycling and decomposition. The combination of high-throughput sequencing and structural equation modeling used here offers an exciting yet under-utilized approach to understanding how both native and non-native species’ range expansions may affect the structure and function of soil ecosystems.