The influence of warming and biotic interactions on the potential for range expansion of native and nonnative species.

Plant species ranges are expected to shift in response to climate change, however, it is unclear how species interactions will affect range shifts. Because of the potential for enemy release of invasive nonnative plant species from species-specific soil pathogens, invasive plants may be able to shift ranges more readily than native plant species. Additionally, changing climatic conditions may alter soil microbial functioning, affecting plant-microbe interactions. We evaluated the effects of site, plant-soil microbe interactions, altered climate, and their interactions on the growth and germination of three congeneric shrub species, two native to southern and central Florida (Eugenia foetida and E. axillaris), and one nonnative invasive from south America (E. uniflora). We measured germination and biomass for these plant species in growth chambers grown under live and sterile soils from two sites within their current range, and one site in their expected range, simulating current (2010) and predicted future (2050) spring growing season temperatures in the new range. Soil microbes (microscopic bacteria, fungi, viruses and other organisms) had a net negative effect on the invasive plant, E. uniflora, across all sites and temperature treatments. This negative response to soil microbes suggests that E. uniflora's invasive success and potential for range expansion are due to other contributing factors, e.g. higher germination and growth relative to native Eugenia. The effect of soil microbes on the native species depended on the geographic provenance of the microbes, and this may influence range expansion of these native species.

Belowground impacts of alpine woody encroachment are determined by plant traits, local climate, and soil conditions.

Global climate and land use change are causing woody plant encroachment in arctic, alpine, and arid/semi-arid ecosystems around the world, yet our understanding of the belowground impacts of this phenomenon is limited. We conducted a globally distributed field study of 13 alpine sites across four continents undergoing woody plant encroachment and sampled soils from both woody encroached and nearby herbaceous plant community types. We found that woody plant encroachment influenced soil microbial richness and community composition across sites based on multiple factors including woody plant traits, site level climate, and abiotic soil conditions. In particular, root symbiont type was a key determinant of belowground effects, as Nitrogen-fixing woody plants had higher soil fungal richness, while Ecto/Ericoid mycorrhizal species had higher soil bacterial richness and symbiont types had distinct soil microbial community composition. Woody plant leaf traits indirectly influenced soil microbes through their impact on soil abiotic conditions, primarily soil pH and C:N ratios. Finally, site-level climate affected the overall magnitude and direction of woody plant influence, as soil fungal and bacterial richness were either higher or lower in woody encroached versus herbaceous soils depending on mean annual temperature and precipitation. All together, these results document global impacts of woody plant encroachment on soil microbial communities, but highlight that multiple biotic and abiotic pathways must be considered to scale up globally from site- and species-level patterns. Considering both the aboveground and belowground effects of woody encroachment will be critical to predict future changes in alpine ecosystem structure and function and subsequent feedbacks to the global climate system.

Shrub range expansion alters diversity and distribution of soil fungal communities across an alpine elevation gradient.

Global climate and land use change are altering plant and soil microbial communities worldwide, particularly in arctic and alpine biomes where warming is accelerated. The widespread expansion of woody shrubs into historically herbaceous alpine plant zones is likely to interact with climate to affect soil microbial community structure and function; however, our understanding of alpine soil ecology remains limited. This study aimed to (i) determine whether the diversity and community composition of soil fungi vary across elevation gradients and to (ii) assess the impact of woody shrub expansion on these patterns. In the White Mountains of California, sagebrush (Artemisia rothrockii) shrubs have been expanding upwards into alpine areas since 1960. In this study, we combined observational field data with a manipulative shrub removal experiment along an elevation transect of alpine shrub expansion. We utilized next-generation sequencing of the ITS1 region for fungi and joint distribution modelling to tease apart effects of the environment and intracommunity interactions on soil fungi. We found that soil fungal diversity declines and community composition changes with increasing elevation. Both abiotic factors (primarily soil moisture and soil organic C) and woody sagebrush range expansion had significant effects on these patterns. However, fungal diversity and relative abundance had high spatial variation, overwhelming the predictive power of vegetation type, elevation and abiotic soil conditions at the landscape scale. Finally, we observed positive and negative associations among fungal taxa which may be important in structuring community responses to global change.