Most tree species predominantly associate with a single type of
mycorrhizal fungi, which can differentially affect plant nutrient
acquisition and biogeochemical cycling. Here, we address for the first
time the impact of mycorrhizal distributions on global carbon and
nutrient cycling. Using the state-of-the-art carbon-nitrogen economics
within the Community Land Model version 5 (CLM5) we found Net Primary
Productivity (NPP) increased throughout the 21st century by 20%;
however, as soil nitrogen has progressively become limiting, the costs
to NPP for nitrogen acquisition — i.e., to mycorrhizae — have
increased at a faster rate by 60%. This suggests that nutrient
acquisition will increasingly demand a higher portion of assimilated
carbon to support the same productivity. Uncertainties in mycorrhizal
distributions are non-trivial, however, with uncertainties in NPP by up
to 345 Tg C yr-1, depending on which published distribution is used.
Remote sensing capabilities for mycorrhizal detection show promise for
refining these estimates further.