Fine-scale diversity patterns in belowground microbial communities are consistent across kingdoms.

The belowground environment is heterogeneous and complex at fine spatial scales. Physical structures, biotic components and abiotic conditions create a patchwork mosaic of potential niches for microbes. Questions remain about mechanisms and patterns of community assembly belowground, including: Do fungal and bacterial communities assemble differently? How do microbes reach the roots of host plants? Within a 4 m2 plot in alpine vegetation, high throughput sequencing of the 16S (bacteria) and ITS1 (fungal) ribosomal RNA genes was used to characterise microbial community composition in roots and adjacent soil of a viviparous host plant (Bistorta vivipara). At fine spatial scales, beta-diversity patterns in belowground bacterial and fungal communities were consistent, although compositional change was greater in bacteria than fungi. Spatial structure and distance-decay relationships were also similar for bacteria and fungi, with significant spatial structure detected at <50 cm among root- but not soil-associated microbes. Recruitment of root microbes from the soil community appeared limited at this sampling and sequencing depth. Possible explanations for this include recruitment from low-abundance populations of soil microbes, active recruitment from neighbouring plants and/or vertical transmission of symbionts to new clones, suggesting varied methods of microbial community assembly for viviparous plants. Our results suggest that even at relatively small spatial scales, deterministic processes play a significant role in belowground microbial community structure and assembly.

Does warming by open-top chambers induce change in the root-associated fungal community of the arctic dwarf shrub Cassiope tetragona (Ericaceae)?

Climate change may alter mycorrhizal communities, which impact ecosystem characteristics such as carbon sequestration processes. These impacts occur at a greater magnitude in Arctic ecosystems, where the climate is warming faster than in lower latitudes. Cassiope tetragona (L.) D. Don is an Arctic plant species in the Ericaceae family with a circumpolar range. C. tetragona has been reported to form ericoid mycorrhizal (ErM) as well as ectomycorrhizal (ECM) symbioses. In this study, the fungal taxa present within roots of C. tetragona plants collected from Svalbard were investigated using DNA metabarcoding. In light of ongoing climate change in the Arctic, the effects of artificial warming by open-top chambers (OTCs) on the fungal root community of C. tetragona were evaluated. We detected only a weak effect of warming by OTCs on the root-associated fungal communities that was masked by the spatial variation between sampling sites. The root fungal community of C. tetragona was dominated by fungal groups in the Basidiomycota traditionally classified as either saprotrophic or ECM symbionts, including the orders Sebacinales and Agaricales and the genera Clavaria, Cortinarius, and Mycena. Only a minor proportion of the operational taxonomic units (OTUs) could be annotated as ErM-forming fungi. This indicates that C. tetragona may be forming mycorrhizal symbioses with typically ECM-forming fungi, although no characteristic ECM root tips were observed. Previous studies have indicated that some saprophytic fungi may also be involved in biotrophic associations, but whether the saprotrophic fungi in the roots of C. tetragona are involved in biotrophic associations remains unclear. The need for more experimental and microscopy-based studies to reveal the nature of the fungal associations in C. tetragona roots is emphasized.

Contrasting emergence of Lyme disease across ecosystems.

Global environmental changes are causing Lyme disease to emerge in Europe. The life cycle of Ixodes ricinus, the tick vector of Lyme disease, involves an ontogenetic niche shift, from the larval and nymphal stages utilizing a wide range of hosts, picking up the pathogens causing Lyme disease from small vertebrates, to the adult stage depending on larger (non-transmission) hosts, typically deer. Because of this complexity the role of different host species for emergence of Lyme disease remains controversial. Here, by analysing long-term data on incidence in humans over a broad geographical scale in Norway, we show that both high spatial and temporal deer population density increase Lyme disease incidence. However, the trajectories of deer population sizes play an overall limited role for the recent emergence of the disease. Our study suggests that managing deer populations will have some effect on disease incidence, but that Lyme disease may nevertheless increase as multiple drivers are involved.