Table 1 The eight categorical predictor variables that were explored in our random-effects meta-analyses

Origin*

5

‘Sympatric’ (all components are from the same geographic location), ‘Allopatric’ (all components are from different geographic locations), ‘Fungi-Soil Sympatric’ (fungus and soil sympatric but allopatric to the plant), Plant-Fungi Sympatric (plant and fungus sympatric but allopatric to the soil), Plant-Soil Sympatric (plant and soil sympatric but allopatric to the fungus)

Plant Functional Group

6

C₄ grasses, C₃ grasses, N-fixing forbs, non-N-fixing forbs, N-fixing woody plants, non-N-fixing woody plants

Inoculum Complexity

3

Whole soil inoculum, multiple species inoculum, single species inoculum

Sterility

2

Sterilized (background soil was sterilized prior to the experiment), not sterilized

Microbe Control

3

Microbial wash (application of aqueous filtrate of non-mycorrhizal microbes), other microbial addition (non-mycorrhizal microbes added via other avenues such as rhizosphere soil from non-mycorrhizal culture plants), no added non-mycorrhizal microbes

Experimental set-up:

2

Laboratory (greenhouse, growth chamber, lathe house or shade house), field

N-fertilization,

P-fertilization

2

Fertilized or not