Fig. 1.

Schematic diagrams of four experimental designs to quantify the activity of the arbuscular mycorrhizal (AM) pathway(s) of uptake: a regular pot containing a specialised hyphal compartment (HC) with labelled soil, e.g. Svenningsen et al. (2018) (a), a split-pot which can be used with or without a HC if one side contains AM fungal inoculum and isotope and the other does not, e.g. Grønlund et al. (2013) (b), a cross-pot with hyphal compartment side arm(s) containing isotope and differential P supply, e.g. Cavagnaro et al. (2005) (c), and a split-plate that allows for detailed and precise tracing experiments including with quantum dots, e.g. Whiteside et al. (2019) (d). Each of these examples uses dual labelling of phosphorus but also could be used with a single isotope/quantum dot or hyphal compartment; the design is dependent on the research question