Elevation Matters More than Season in Shaping the Heterogeneity of Soil and Root Associated Ectomycorrhizal Fungal Community

Altitude and season represent two important environmental gradients that shape the structure of biome, including the heterogeneity of EcM fungi. Previous studies have separately considered the influences of altitude and season on EcM fungal communities, but the relative importance of altitude and season is still unknown.

Ectomycorrhizal fungal composition and function predict tree growth across Europe

<p>Ectomycorrhizal fungi are central members of the forest fungal community, forming symbiosis with most trees in temperate and boreal forests, enhancing plant access to limiting soil nutrients. Decades of greenhouse studies have shown that specific mycorrhizal fungi enhance tree seedlings growth and nutrient uptake rates, and that these effects are sustained when seedlings are out-planted into regenerating forests. Whether these relationships scale up to affect the growth of mature trees and entire forests harboring diverse fungal communities remains unknown. In this study, we combined a continental set of European forest inventory data from the ICP forest network with molecular ectomycorrhizal fungal community surveys to identify features of the mycorrhizal mycobiome linked to forest productivity. We found that ectomycorrhizal fungal community composition was a key predictor of tree growth, and this effect was robust to statistically accounting for climate, nitrogen deposition, soil inorganic nitrogen availability, soil pH, and forest stand characteristics. Furthermore, ectomycorrhizal fungi with greater genomic investment in energy production and inorganic nitrogen metabolism, but lower investment in organic nitrogen acquisition, were linked to faster tree growth. Lastly, we sampled soils from fast and slow growing forests and introduced their microbiomes into a sterilized growth medium to experimentally isolate microbiome effects on tree development. Consistent with our observational analysis, tree seedling growth was accelerated when inoculated with microbiomes from fast vs. slow growing forests.  By linking molecular community surveys and long-term forest inventory data in the field, and then pairing this with a microbiome manipulation study under controlled conditions, this work demonstrates an emerging link between the forest microbiome and dominant European tree growth rates.</p>

Large-scale insect outbreak homogenizes the spatial structure of ectomycorrhizal fungal communities

Ectomycorrhizal fungi (plant symbionts) are diverse and exist within spatially variable communities that play fundamental roles in the functioning of terrestrial ecosystems. However, the underlying ecological mechanisms that maintain and regulate the spatial structuring of ectomycorrhizal fungal communities are both complex and remain poorly understood. Here, we use a gradient of mountain pine beetle (Dendroctonus ponderosae) induced tree mortality across eleven stands in lodgepole pine (Pinus contorta) forests of western Canada to investigate: (i) the degree to which spatial structure varies within this fungal group, and (ii) how these patterns may be driven by the relative importance of tree mortality from changes in understory plant diversity, productivity and fine root biomass following tree death. We found that the homogeneity of the ectomycorrhizal fungal community increased with increasing tree death, aboveground understory productivity and diversity. Whereas, the independent effect of fine root biomass, which declined along the same gradient of tree mortality, increased the heterogeneity of the ectomycorrhizal fungal community. Together, our results demonstrate that large-scale biotic disturbance homogenizes the spatial patterns of ectomycorrhizal fungal communities.