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.