Carbon partitioning in a split‐root system of arbuscular mycorrhizal plants is fungal and plant species dependent

• Root carbon (C) partitioning in two host plant species colonized by one of three arbuscular mycorrhizal (AM) fungal species was investigated. • Split-root systems of barley (Hordeum vulgare) and sugar maple (Acer saccharum) were inoculated on one side with one of three AM fungi. Leaves were labelled with ¹⁴ CO₂ 3 wk after inoculation. Plants were harvested 24 h later and the root systems from the mycorrhizal (M) and nonmycorrhizal (NM) sides were analysed separately for ¹⁴ C. • Partitioning of ¹⁴ C between M and NM sides varied depending on the fungal and host plant species used. Gigaspora rosea showed a strong C-sink capacity with both plant species, Glomus intraradices showed a strong C-sink capacity with barley, and Glomus mosseae did not affect ¹⁴ C partitioning. The C-sink strength of the M barley roots inoculated with G. rosea or G. intraradices was linearly correlated with the degree of colonization. • The use of three AM fungal and two plant species allowed us to conclude that C-sink strength of AM fungi depends on both partners involved in the symbiosis.