Nitrogen impacts on ectomycorrhizal fungi: from resource exchange to forest carbon cycling.

Inorganic nitrogen (N) is known to influence the composition and functioning of ectomycorrhizal (ECM) fungal communities. Research consistently highlights fungal traits related to carbon (C) use as key determinants of fungal sensitivity to elevated inorganic N, with more C-demanding ECM fungi declining along inorganic N gradients. This decline is often attributed to reduced C allocation from host trees to their fungal symbionts, yet the precise mechanisms underlying this reduction remain unclear, despite significant research efforts. Here, I examine recent advances in this field which highlight the role of fungal nutritional requirements and source-sink dynamics in regulating C flow to ECM fungi. Additionally, I explore how N-induced shifts in ECM fungal communities impact biogeochemical cycles, potentially leading to globally significant changes in decomposition and C-sequestration rates in forest soils. Given the scale of these potential effects, further research is essential to fully understand the complexity of N-driven changes in ECM fungal functioning.