A significant fraction of carbon stored in the Earth’s soil moves through arbuscular mycorrhiza(AM) and ectomycorrhiza (EM). The impacts of AM and EM on the soil carbon budgetare poorly understood... Show moreA significant fraction of carbon stored in the Earth’s soil moves through arbuscular mycorrhiza(AM) and ectomycorrhiza (EM). The impacts of AM and EM on the soil carbon budgetare poorly understood.We propose a method to quantify the mycorrhizal contribution to carbon cycling, explicitlyaccounting for the abundance of plant-associated and extraradical mycorrhizal mycelium. Wediscuss the need to acquire additional data to use our method, and present our new globaldatabase holding information on plant species-by-site intensity of root colonization by mycorrhizas.We demonstrate that the degree of mycorrhizal fungal colonization has globally consistentpatterns across plant species. This suggests that the level of plant species-specific rootcolonization can be used as a plant trait.To exemplify our method, we assessed the differential impacts of AM : EM ratio and EMshrub encroachment on carbon stocks in sub-arctic tundra. AM and EM affect tundra carbonstocks at different magnitudes, and via partly distinct dominant pathways: via extraradicalmycelium (both EM and AM) and via mycorrhizal impacts on above- and belowground biomasscarbon (mostly AM).Our method provides a powerful tool for the quantitative assessment of mycorrhizal impacton local and global carbon cycling processes, paving the way towards an improved understandingof the role of mycorrhizas in the Earth’s carbon cycle. Show less
