Abstract:
Mycorrhizal fungi regulate forest and nutrient dynamics, including soil carbon, in boreal and temperate forests. However, the drivers of their distribution and whether they change over time remain unknown. Using a network of 139 forest sites across Europe and the UK, we explore the biogeographic and ecological mechanisms underlying species’ spatial distribution. Using snapshot resampling, for the first time, we quantify how forest mycorrhizal communities change over time and identify the main drivers of these changes. By measuring physiological fungal traits, we link species properties to their responses to environmental change and their potential effects on soil carbon content.
Ectomycorrhizal diversity is driven mainly by host trees, climate, and atmospheric nitrogen pollution. Community composition responds to the same drivers and shows some biogeographic structuring across ecoregions. Over time, diversity increased despite major shifts in species composition, with some abundant species showing up to a 50% decrease in abundance over ~10 years. Ectomycorrhizal communities across Europe show signs of homogenisation, potentially due to an increase in nitrophilic species accompanied by northward and southward migrations.
Changes in precipitation, temperature, and nitrogen deposition are the main drivers of change in ectomycorrhizal communities over time. Finally, atmospheric inorganic nitrogen deposition selects against species specialised in organic nitrogen foraging, potentially impacting soil carbon storage capacity. These results suggest that large-scale shifts in mycorrhizal composition over time can lead to changes in nutrient dynamics across European forests.
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