Table 1.

Detailed specification of the effects of mechanical stress on root and root system morphology

Effect	Stress conditions	Species	References
Reduced root system size	compacted soil	Avena sativa	Schuurman (1965)
	compacted soil	Oryza sativa, Sorghum bicolor, Zea mays, Coix lacryma-jobi	Iijima and Kono (1991)
	compacted sand	Lolium perenne, Trifolium repens, Agrostis capillaris	Cook et al. (1996)
	compacted soil	Hordeum vulgare	Mulholland et al. (1996a)
	compacted soil	Z. mays, ×Triticosecale	Grzesiak (2009)
	compacted soil	Triticum aestivum, Secale cereale, Triticosecale Wittmack, Z. mays	Lipiec et al. (2012)
	compacted soil	Pisum sativum, Acacia salicina, Eucalyptus camaldulensis, E. leucoxylon, E. kochii	Azam et al. (2014)
	compacted soil	T. aestivum	Chen et al. (2014)
	glass beads	Z. mays	Groleau-Renaud et al. (1998)
	large soil aggregates	Z. mays	Donald et al. (1987); Alexander and Miller (1991)
	pressurized glass beads	H. vulgare	Goss and Drew (1972)
Reduced individual root length	compacted soil compacted sand compacted soil compacted soil compacted soil compacted sand compacted soil large soil aggregates glass beads pressurized soil/glass beads pressurized glass beads pressurized soil pressurized glass beads compression (apparatus) changed orientation	O. sativa, S. bicolor, Z. mays, C. lacryma-jobi L. perenne, T. repens, A. capillaris Z. mays Prunus persica H. vulgare Lupinus angustifolius T. aestivum Z. mays Z. mays H. vulgare, O. sativa H. vulgare, T. aestivum, Z. mays, Beta vulgaris P. sativum Z. mays Z. mays Arabidopsis thaliana	Iijima and Kono (1991) Cook et al. (1996) Konôpka et al. (2009) Bécel et al. (2012) Loades et al. (2013) Chen et al. (2014) Colombi et al. (2017) Donald et al. (1987) Moss et al. (1988), Groleau-Renaud et al. (1998) Abdalla et al. (1969) Goss (1977) Castillo et al. (1982) Veen (1982) Barley (1962) Okamoto et al. (2008)
Increased root diameter (root swelling)	compacted soil/sand compacted soil compacted soil compacted soil/sand compacted soil compacted soil compacted soil compacted soil compacted soil large soil aggregates glass beads pressurized soil/glass beads pressurized glass beads pressurized soil/glass beads pressurized sand axial loading (apparatus) rigid tubes changed orientation	L. angustifolius Z. mays 22 monocotyledonous and dicotyledonous species P. sativum Glycine max Nicotiana tabacum H. vulgare P. sativum, A. salicina, E. camaldulensis, E. leucoxylon, E. kochii T. aestivum Z. mays Z. mays H. vulgare, O. sativa H. vulgare Z. mays L. angustifolius Z. mays Z. mays A. thaliana	Atwell (1988); Chen et al. (2014) Bengough and Mullins (1991); Konôpka et al. (2009) Materechera et al. (1991) Croser et al. (1999); Kirby and Bengough (2002) Ramos et al. (2010) Alameda et al. (2012) Loades et al. (2013, 2015) Azam et al. (2014) Colombi et al. (2017) Donald et al. (1987); Logsdon et al. (1987) Moss et al. (1988) Abdalla et al. (1969) Goss and Russell (1980) Veen (1982); Sarquis et al. (1991) Hanbury and Atwell (2005) Kuzeja et al. (2001) Potocka et al. (2011) Okamoto et al. (2008)
Flattened roots	compacted soil compacted soil rigid tubes	G. max H. vulgare, Triticosecale Wittmack Z. mays	Ramos et al. (2010) Lipiec et al. (2012) Potocka et al. (2011)
Root bending/buckling	compacted soil two-layer phytagel medium two-layer gel medium artificial obstacle (horizontal barrier) rigid tubes artificial obstacle (vertical barrier)	Z. mays (bending) A. thaliana (bending) Medicago truncatula (helical buckling) A. thaliana (bending) Z. mays (buckling) Populus deltoides × P. nigra (bending)	Konôpka et al. (2009) Yamamoto et al. (2008); Yan et al. (2017) Silverberg et al. (2012) Massa and Gilroy (2003) Potocka et al. (2011) Bizet et al. (2016)
Wavy root phenotype	changed orientation	A. thaliana	Okada and Shimura (1990); Rutherford and Masson (1996); Buer et al. (2000); Thompson and Holbrook (2004)
Altered branching Increased number of lateral roots Increased branching density Reduced number of lateral roots Decreased branching density Altered distribution of lateral roots Laterals formed close to root tip	pressurized glass beads bending bending bending compacted soil compacted soil pressurized glass beads compacted sand compacted soil pressurized glass beads compacted sand compacted soil slope soil conditions compacted soil compacted soil pressurized glass beads	Z. mays Fraxinus ornus P. nigra A. thaliana P. sativum Z. mays H. vulgare L. perenne, T. repens, A. capillaris Z. mays, ×Triticosecale H. vulgare T. repens L. angustifolius Spartium junceum L. angustifolius G. max H. vulgare	Veen (1982) Chiatante et al. (2007) Scippa et al. (2008) Ditengou et al. (2008); Richter et al. (2009) Tsegaye and Mullins (1994) Konôpka et al. (2009) Goss and Drew (1972) Cook et al. (1996) Grzesiak (2009) Goss (1977) Cook et al. (1996) Chen et al. (2014) Chiatante et al. (2003); Lombardi et al. (2017) Atwell (1988) Ramos et al. (2010) Goss and Drew (1972); Goss (1977)
Reduced cap size	compacted sand pressurized glass beads artificial obstacle (horizontal barrier)	Z. mays H. vulgare Z. mays	Iijima et al. (2003a) Wilson and Robards (1979) Souty and Rode (1987)