Leroy et al. (2022); Spitzer et al. (2022); Yang et al. (2022)

Dallstream et al. (2022)*; Erktan et al. (2022); Gagliardi et al. (2022); Klimešová et al. (2022)*; Kotowska et al. (2022); Mafa-Attoye et al. (2022); Mao et al. (2022); Merino-Martin et al. (2022); Pierick et al. (2022); Stiblíková et al. (2022)*; Spitzer et al. (2022);

Alonso-Crespo et al. (2022); Dallstream et al. (2022)*; Kotowska et al. (2022); Schuster et al. (2022); Slette et al. (2022); Weemstra et al. (2022)*; Yang et al. (2022)

Dai et al. (2022); Dallstream et al. (2022)*; Erktan et al. (2022); Gagliardi et al. (2022); Guo et al. (2022); Klimešová et al. (2022)*; Kotowska et al. (2022); Leroy et al. (2022); Mafa-Attoye et al. (2022); Mao et al. (2022); Merino-Martin et al. (2022); Pierick et al. (2022); Stiblíková et al. (2022)*; Slette et al. (2022); Spitzer et al. (2022); Wang et al. (2022); Weemstra et al. (2022)*; Yang et al. (2022)

Dai et al. (2022); Dallstream et al. (2022)*; Gagliardi et al. (2022); Klimešová et al. (2022)*; Leroy et al. (2022); Merino-Martin et al. (2022); Stiblíková et al. (2022)*; Weemstra et al. (2022)*

Dallstream et al. (2022)*; Wang et al. (2022)

Alonso-Crespo et al. (2022); Dallstream et al. (2022)*; Gagliardi et al. (2022); Klimešová et al. (2022); Leroy et al. (2022); Mafa-Attoye et al. (2022); Merino-Martin et al. (2022); Schuster et al. (2022); Stiblíková et al. (2022)*; Wang et al. (2022); Weemstra et al. (2022)*; Yang et al. (2022)

Climate region	Reference in this Special Issue
Temperate	Alonso-Crespo et al. (2022); Erktan et al. (2022); Klimešová & Herben (2022); Mafa-Attoye et al. (2022); Mao et al. (2022); Merino-Martin et al. (2022); Schuster et al. (2022); Slette et al. (2022); Yang et al. (2022)
(Sub)Tropical	Dai et al. (2022); Dallstream et al. (2022); Gagliardi et al. (2022); Guo et al. (2022); Leroy et al. (2022); Kotowska et al. (2022); Pierick et al. (2022)
(Sub)Arctic	Spitzer et al. (2022)
Taxonomic scale
Community	Alonso-Crespo et al. (2022); Erktan et al. (2022); Guo et al. (2022); Kotowska et al. (2022); Mafa-Attoye et al. (2022); Merino-Martin et al. (2022); Pierick et al. (2022); Schuster et al. (2022); Slette et al. (2022); Spitzer et al. (2022); Weemstra et al. (2022)*
Species	Dai et al. (2022); Dallstream et al. (2022); Klimešová et al. (2022); Mao et al. (2022); Spitzer et al. (2022); Stiblíková et al. (2022); Weemstra et al. (2022); Yang et al. (2022)
Individual (within species)	Gagliardi et al. (2022); Leroy et al. (2022); Mao et al. (2022); Spitzer et al. (2022); Wang et al. (2022)
Root trait category
Anatomy (e.g., stele diameter, absence/presence of arbuscules)	Leroy et al. (2022)
Architecture (e.g., branching intensity, root tip density)	Leroy et al. (2022); Spitzer et al. (2022); Yang et al. (2022)
Chemistry (e.g., root concentration of nitrogen, secondary compounds)	Dallstream et al. (2022); Erktan et al. (2022); Gagliardi et al. (2022); Klimešová et al. (2022); Kotowska et al. (2022); Mafa-Attoye et al. (2022); Mao et al. (2022); Merino-Martin et al. (2022); Pierick et al. (2022); Stiblíková et al. (2022)*; Spitzer et al. (2022);
Dynamics (e.g., root lifespan, root production)	Alonso-Crespo et al. (2022); Dallstream et al. (2022); Kotowska et al. (2022); Schuster et al. (2022); Slette et al. (2022); Weemstra et al. (2022); Yang et al. (2022)
Mechanics (e.g., toughness, tensile strength)	Mao et al. (2022)
Morphology (e.g., specific root length, root diameter)	Dai et al. (2022); Dallstream et al. (2022); Erktan et al. (2022); Gagliardi et al. (2022); Guo et al. (2022); Klimešová et al. (2022); Kotowska et al. (2022); Leroy et al. (2022); Mafa-Attoye et al. (2022); Mao et al. (2022); Merino-Martin et al. (2022); Pierick et al. (2022); Stiblíková et al. (2022); Slette et al. (2022); Spitzer et al. (2022); Wang et al. (2022); Weemstra et al. (2022); Yang et al. (2022)
Microbial (e.g., mycorrhizal type, endosphere community composition)	Dai et al. (2022); Dallstream et al. (2022); Gagliardi et al. (2022); Klimešová et al. (2022); Leroy et al. (2022); Merino-Martin et al. (2022); Stiblíková et al. (2022); Weemstra et al. (2022)
Physiology (e.g., enzyme activity, nutrient uptake)	Dallstream et al. (2022)*; Wang et al. (2022)
System (e.g., root mass fraction, maximum rooting depth)	Alonso-Crespo et al. (2022); Dallstream et al. (2022); Gagliardi et al. (2022); Klimešová et al. (2022); Leroy et al. (2022); Mafa-Attoye et al. (2022); Merino-Martin et al. (2022); Schuster et al. (2022); Stiblíková et al. (2022); Wang et al. (2022); Weemstra et al. (2022)*; Yang et al. (2022)