Climate change is altering soil microbial communities worldwide, particularly in arctic and alpine biomes where warming is accelerated. Concurrently, alpine plant communities are shifting, including the widespread expansion of woody shrubs into historically herbaceous alpine grasslands and fellfields. This is likely to have interacting effects with climate on soil microbial community structure and function, however our baseline understanding of microbial biogeography in alpine environments remains limited. Therefore, this study aims to 1) determine whether alpine soil fungi follow predictable patterns of diversity and community composition across elevation and to 2) assess the impact of woody shrub expansion on these patterns. In the White Mountains of California, Sagebrush (Artemisia rothrockii) shrubs are expanding upwards into alpine areas at a rate of 30 m/decade since 1960. We sampled soils from under and outside sagebrush canopies and from sagebrush removal plots at 3200, 3500, and 3800 m elevation, spanning the observed range expansion of A. rothrockii. We measured environmental covariates including soil nutrients, water and pH for each sample. We extracted DNA and used fungal-specific primers of the ITS1 region for sequencing on the Illumina MiSeq platform and utilized the “Hierarchical Modeling of Species Communities” (HMSC) framework in our statistical analyses.
Fungal diversity and richness decreased significantly with elevation but not with vegetation type (shrub, shrub interspace, shrub removal). The low elevation (3200 m) site had significantly higher richness and diversity than both the middle (3500m) and high (3800m) sites. Fungal community composition (bray Curtis dissimilarity) was distinct across elevation, vegetation type, and their interaction. Shrub community composition differed from interspace and shrub removal soils and all elevation sites were significantly different from each other. Relative abundance of fungal families differed by vegetation type and elevation. Specifically, families within the Agaricomycetes were found in higher abundance in shrub and shrub removal plots as well as high elevation sites. These fungi are commonly saprotrophic, wood or litter decaying fungi. In contrast, shrub interspace soils had increased prevalence of the family Puccinaceae, a known plant pathogen of rust fungi. However, HMSC analysis revealed that environmental covariates including microbial biomass N and soil organic carbon (SOC), were equally good if not better predictors of relative fungal group abundance than either elevation or vegetation type. In addition, variance partitioning showed that the random effects of spatial variation in fungal taxa overwhelmed the explanatory power of elevation, vegetation type and environmental covariates.