Skip to main content

View full-text article in PMC

. 2024 Apr 7;8(4):e582. doi: 10.1002/pld3.582

TABLE 1.

Root hydraulic properties definitions.

Symbol	Definition	Tissue level	Units	Alternative symbols used in the literature	Specification
k _r	Radial hydraulic conductivity	Individual roots or root segments	m MPa⁻¹ s⁻¹	L _r (Doussan et al., 2006; Huang & Nobel, 1994; North & Peterson, 2005)	Usually not directly measured, but calculated using k _root and k _x measurements, based on the model of Landsberg and Fowkes (1978).
k _x	Specific axial hydraulic conductance	Individual roots or root segments	m⁴ MPa⁻¹ s⁻¹	K _h (Doussan et al., 2006; Huang & Nobel, 1994; North & Peterson, 2005); K _x (Ahmed et al., 2018); L _x (Frensch & Steudle, 1989; Melchior & Steudle, 1993)	The ability of roots to transport water longitudinally
k _{x_cs}	k _x normalized by cross sectional area	Individual roots or root segments	m² MPa⁻¹ s⁻¹	K _s (Choat et al., 2012; Pratt et al., 2007)	k _x data for woody species is very commonly reported on a cross sectional area basis (sapwood, stele, total root cross section)
k _root	(Total) root hydraulic conductivity	Individual roots or root segments	m MPa⁻¹ s⁻¹	L _pr (Boursiac, Protto, et al., 2022; Kim et al., 2018; Steudle, 2000a); L _p (Gambetta et al., 2017; Huang & Nobel, 1994; Lambers & Oliveira, 2019; North & Peterson, 2005)	The total water transport capacity of an individual root or a root segment. It can be separated into its radial and axial components. Often assumed to be an approximation of k _r in the literature (i.e., water transport only limited by k _r, not by k _x
K _rs	Whole root system conductance	Entire root system	m³ MPa⁻¹ s⁻¹	K _root (Cai et al., 2022); L _p (Lambers & Oliveira, 2019); L _pr (Kim et al., 2018; Steudle, 2000a), L ₀ (Boursiac, Protto, et al., 2022; Maurel et al., 2010; Tyerman et al., 2017)	The water transport capacity of the entire root system.
K _{rs_norm}	K _rs normalized by a measure of the root system size	Entire root system	Depends on normalization		Most common normalizations found in the literature include:Root surface area: K _{rs_area} (m MPa⁻¹ s⁻¹);Root fresh or dry weight: K _{rs_weight} (m³ MPa⁻¹ s⁻¹ g⁻¹);Root length: K _{rs_length} (m³ MPa⁻¹ s⁻¹ m⁻¹); Root volume: K _{rs_vol} (m³ MPa⁻¹ s⁻¹ m⁻³)