TABLE 3.

Factors affecting root hydraulic properties variability. Factors analyzed and their ranges (or factor levels) observed in the database.

Factor	Description	Factor levels or range
PFT	Plant functional types, according to the classification in Table 2	Nine different PFTs
Age	Root system age.Data principally corresponds to dicot crops and grasses. Root system age of trees and shrubs scarcely reported, mainly restricted to studies with seedlings	3–150 days (herbaceous crops and grasses);12–485 days (woody crops)
Driving force	Driving force used for measurement of root hydraulic properties	Hydrostatic or osmotic driving force
Genus	Taxonomic genus	124 distinct genera
Growth form	A coarser classification than PFT	Tree, shrub, succulent, graminoid or dicot crops
Root section	Section of the root (segment) for which root hydraulic properties were determined. Several investigations measured whole roots instead of specific segments	Whole root or distal, mid‐root or basal segments
Root type	Type of root investigated	Primary, tap, seminal, lateral, adventitious, whole root system
Species	Species investigated	214 distinct species
Treatment	Simplified classification of the experimental treatments applied in the studies	Control, stress, other or no treatment