Table 1.

Plant species, response variables extracted, subgroup of the response variable extracted and references used in the meta-analysis.

Species	Response variable extracted				Subgroup of the response variable extracted			References
	Shoot %N	Root %N	Root N-uptake rate	Protein concentration	Growth form	Functional group	Treatment technique
Abutilon theophrasti	*	*			NWD	NL	GC	Coleman and Bazzaz (1992)
Acer rubrum	*				W	NL	OTC	Norby et al. (2000)
Acer rubrum		*			W	NL	OTC	Wan et al. (2004)
Acer rubrum	*				W	NL	OTC	Williams et al. (2003)
Acer rubrum	*				W	NL	OTC	Williams et al. (2000)
Acer saccharum	*				W	NL	OTC	Norby et al. (2000)
Acer saccharum		*			W	NL	OTC	Wan et al. (2004)
Acer saccharum	*				W	NL	OTC	Williams et al. (2000)
Alliaria petiolata	*				NWD	NL	GC	Anderson and Cipollini (2013)
Amaranthus retroflexus	*	*			NWD	NL	GC	Coleman and Bazzaz (1992)
Betula pendula			*		W	NL	GC	Kellomaki and Wang (2001)
Betula pendula	*				W	NL	CTC	Kuokanen et al. (2001)
Betula pendula	*				W	NL	CTC	Kuokanen et al. (2003)
Betula pendula	*				W	NL	CTC	Lavola et al. (2013)
Brassica juncea	*				NWD	NL	GC	Seth and Misra (2014)
Calluna vulgaris	*	*			W	NL	FACE	Andresen et al. (2009)
Calluna vulgaris	*	*			W	NL	FACE	Andresen et al. (2010)
Calluna vulgaris			*		W	NL	FACE	Arndal et al. (2014)
Coffea arabica	*				G	NL	GC	Ramalho et al. (2018)
Deschampsia flexuosa	*	*			W	NL	FACE	Andresen et al. (2009)
Deschampsia flexuosa	*	*			G	NL	FACE	Andresen et al. (2010)
Deschampsia flexuosa			*		G	NL	FACE	Arndal et al. (2014)
Echinium plantagineum	*				NWD	NL	GC	Johns and Hughes (2002)
Eucalyptus globulus	*				W	NL	CTC	Crous et al. (2013)
Eucalyptus globulus	*				W	NL	OTC	Sharwood et al. (2017)
Eucalyptus robusta	*				W	NL	GH	Gherlenda et al. (2015)
Eucalyptus saligna	*				W	NL	GH	Ayub et al. (2011)
Eucalyptus saligna	*				W	NL	GH	Ghannoum et al. (2010a)
Eucalyptus saligna	*	*			W	NL	GH	Ghannoum et al. (2010b)
Eucalyptus sideroxylon	*				W	NL	GH	Ghannoum et al. (2010a)
Eucalyptus sideroxylon	*	*			W	NL	GH	Ghannoum et al. (2010b)
Eucalyptus tereticornis	*				W	NL	GH	Gherlenda et al. (2015)
Eucalyptus tereticornis	*				W	NL	GH	Gherlenda et al. (2016)
Eucalyptus tereticornis	*				W	NL	GH	Murray et al. (2013)
Geum vernum	*				NWD	NL	GC	Anderson and Cipollini (2013)
Glycine max				*	NWD	L	OTC	Palacios et al. (2019)
Glycine max				*	NWD	L	OTC	Qiao et al. (2019)
Glycine max	*				NWD	L	FACE	Rosenthal et al. (2014)
Gossypium hirsutum	*				W	NL	GC	Zhang et al. (2017)
Grasses	*				G	NL	GC	Johnson and Hartley (2018)
Lantana camara	*				W	NL	GC	Johns et al. (2003)
Lolium perenne	*	*			G	NL	CTC	Soussana et al. (1996)
Lolium perenne	*				G	NL	CTC	Zavalloni et al. (2012)
Lotus corniculatus	*				NWD	L	CTC	Zavalloni et al. (2012)
Medicago lupulina	*				NWD	L	CTC	Zavalloni et al. (2012)
Medicago sativa	*				NWD	L	TGT	Aranjuelo et al. (2005)
Medicago sativa		*			NWD	L	TGT	Aranjuelo et al. (2008)
Medicago sativa	*				NWD	L	GH	Ariz et al. (2015)
Oryza sativa				*	G	NL	FACE	Jing et al. (2016)
Oryza sativa	*				G	NL	TGT	Kim et al. (2011)
Oryza sativa	*	*			G	NL	FACE	Li et al. (2017)
Oryza sativa	*				G	NL	OTC	Liu et al. (2019)
Panicum maximum	*				G	NL	FACE	de Assis Prado et al. (2016)
Phalaris aquatica	*				G	NL	TGT	Lilley et al. (2001)
Phalaris aquatica	*				G	NL	TGT	Volder et al. (2015)
Phaseolus vulgaris	*				NWD	L	CTC	Prasad et al. (2004)
Pinus ponderosa		*			W	NL	GH	King et al. (1997)
Pinus sylvestris	*				W	NL	CTC	Luomala et al. (2003)
Pinus taeda		*			W	NL	GH	King et al. (1997)
Plantago lanceolata	*				G	NL	CTC	Zavalloni et al. (2012)
Poa pratensis	*				G	NL	CTC	Zavalloni et al. (2012)
Pseudotsuga menziesii		*			W	NL	CTC	Chen et al. (2008)
Pseudotsuga menziesii	*				W	NL	CTC	Hobbie et al. (2001)
Quercus robur	*				W	NL	GH	Dury et al. (1998)
Rumex acetosa	*				NWD	NL	CTC	Zavalloni et al. (2012)
Salix myrsinifolia	*				W	NL	CTC	Veteli et al. (2002)
Semiarid grasses	*	*			G	NL	FACE	Dijkstra et al. (2010)
Solanum lycopersicum	*	*	*	*	NWD	NL	GC	Jayawardena et al. (2017)
Solanum lycopersicum	*	*	*	*	NWD	NL	GC	Jayawardena et al. (2021)
Species mix		*			N/A	NL	CTC	Kandeler et al. (1998)
Species mix	*				N/A	NL	FACE	Mueller et al. (2016)
Species mix		*			G	NL	CTC	Zavalloni et al. (2012)
Trifolium subterraneum	*				NWD	L	TGT	Lilley et al. (2001)
Triticum aestivum	*	*	*	*	G	NL	GC	Jayawardena et al. (2020)
Triticum durum	*				NWD	NL	TGT	Jauregui et al. (2015)
Vitis vinifera	*	*			W	NL	GH	Salazar-Parra et al. (2015)
Zea mays				*	G	NL	OTC	Abebe et al. (2016)
Zea mays	*				G	NL	CTC	Kim et al. (2007)
Zea mays				*	G	NL	OTC	Qiao et al. (2019)

References included in the meta-analysis are available in Supporting Information—Appendix S2.

* denotes the response variable extracted from each reference. Different growth forms are denoted as woody, W; grassy, G; and non-woody dicot, NWD. Different functional groups are denoted as legume, L; and non-legume, NL. Different treatment techniques are denoted as open-top chambers, OTC; closed-top chambers, CTC; greenhouses, GH; free-air CO₂ enrichment, FACE; temperature-gradient tunnels, TGT; and growth chambers, GC.