be significantly important traits for soil penetration, enhancing rooting depth away
from the soil surface and root length density (RLD), with profuse fine roots accommodating large surface area and root volume (Satpute et al. unpublished), the traits
deemed essential for water extraction during soil moisture stress. However, deep or
profuse rooting would have no effect in shallow soil, in soil where there is no water
at depth, or under conditions of mild water stress (Vadez 2014). A modeling study in
soybean has shown that increasing the rate of rooting depth would lead to faster soil
depletion and yield penalties, especially in the driest quartile of the years, and there
would be no benefit, but even a penalty from faster and deeper rooting (Sinclair et al.
2010). A relationship between water extraction and RLD could be resolved to some
extent, using root development model that is capable of reconstituting root system
architecture in a 3-D context (de Dorlodot et al. 2007; Draye et al. 2010; Pages et al.
2010; Lobet et al. 2011), which gives power to interpret water extraction data for
harnessing the genetics of the components of this architecture such as root angles,
different types of roots, branching patterns, etc. (Draye et al. 2010; Lobet et al. 2011;
Lynch and Brown 2012). The conditions to the success of this breeding strategy are
that water would be available at depth (deep soil and water available at depth); deepwater extraction would have an increased benefit if it took place during the grain
filling period and that might imply searching for genetic material capable of sustaining root growth during reproductive development; and cropping conditions of
moderate VPD in crops where this potential extra water uptake from deep rooting
would represent a large proportion of the total transpirational water needs (Vadez
2014).
An alternative way to approach the role of root for water stress adaptation, using a
lysimetric system, is assessing water extraction by roots as a way to harness the
functionality of root systems. Roots need to be looked at with a view to the whole
plant (Comas et al. 2013) and resource availability in time and space (Lynch 2013).
Programs need to focus on traits regulating the rate at which plants use the available
water before and during stress, involving roots in the sensing mechanism of water
stress. The capacity to extract the available water at depth is probably critical and
may come from deep roots having a high hydraulic conductivity (Vadez 2014).
Certain root anatomical traits, including xylem vessel size and abundance, root
cortical aerenchyma, the number of root cells or the number of root cell files,
contributing to drought adaptation as the building blocks of its hydraulic properties,
eventually affect critical plant water-budget traits.
The current model of water uptake through the root cylinder to the xylem, the
composite transport model, is such that water is taken up via two major pathways. In
an apoplastic pathway, a large part of that water travels across the intercellular space
between cells (apoplast) in the root cortex, toward the endodermis and the xylem
vessels. The exodermis could represent a variable apoplastic barrier that plants could
use to modulate their water transport characteristics (Hose et al. 2001). The resistance to water flow usually increases under water deficit (Steudle 2000). Most of that
resistance is located in the root cylinder (radial resistance), whereas xylem vessels
normally offer much less resistance (axial resistance) (Steudle 2000). Another pathway is symplastic water transfer. During the night in the absence of transpiration,
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G. K. Satpute et al.
from the soil surface and root length density (RLD), with profuse fine roots accommodating large surface area and root volume (Satpute et al. unpublished), the traits
deemed essential for water extraction during soil moisture stress. However, deep or
profuse rooting would have no effect in shallow soil, in soil where there is no water
at depth, or under conditions of mild water stress (Vadez 2014). A modeling study in
soybean has shown that increasing the rate of rooting depth would lead to faster soil
depletion and yield penalties, especially in the driest quartile of the years, and there
would be no benefit, but even a penalty from faster and deeper rooting (Sinclair et al.
2010). A relationship between water extraction and RLD could be resolved to some
extent, using root development model that is capable of reconstituting root system
architecture in a 3-D context (de Dorlodot et al. 2007; Draye et al. 2010; Pages et al.
2010; Lobet et al. 2011), which gives power to interpret water extraction data for
harnessing the genetics of the components of this architecture such as root angles,
different types of roots, branching patterns, etc. (Draye et al. 2010; Lobet et al. 2011;
Lynch and Brown 2012). The conditions to the success of this breeding strategy are
that water would be available at depth (deep soil and water available at depth); deepwater extraction would have an increased benefit if it took place during the grain
filling period and that might imply searching for genetic material capable of sustaining root growth during reproductive development; and cropping conditions of
moderate VPD in crops where this potential extra water uptake from deep rooting
would represent a large proportion of the total transpirational water needs (Vadez
2014).
An alternative way to approach the role of root for water stress adaptation, using a
lysimetric system, is assessing water extraction by roots as a way to harness the
functionality of root systems. Roots need to be looked at with a view to the whole
plant (Comas et al. 2013) and resource availability in time and space (Lynch 2013).
Programs need to focus on traits regulating the rate at which plants use the available
water before and during stress, involving roots in the sensing mechanism of water
stress. The capacity to extract the available water at depth is probably critical and
may come from deep roots having a high hydraulic conductivity (Vadez 2014).
Certain root anatomical traits, including xylem vessel size and abundance, root
cortical aerenchyma, the number of root cells or the number of root cell files,
contributing to drought adaptation as the building blocks of its hydraulic properties,
eventually affect critical plant water-budget traits.
The current model of water uptake through the root cylinder to the xylem, the
composite transport model, is such that water is taken up via two major pathways. In
an apoplastic pathway, a large part of that water travels across the intercellular space
between cells (apoplast) in the root cortex, toward the endodermis and the xylem
vessels. The exodermis could represent a variable apoplastic barrier that plants could
use to modulate their water transport characteristics (Hose et al. 2001). The resistance to water flow usually increases under water deficit (Steudle 2000). Most of that
resistance is located in the root cylinder (radial resistance), whereas xylem vessels
normally offer much less resistance (axial resistance) (Steudle 2000). Another pathway is symplastic water transfer. During the night in the absence of transpiration,
88
G. K. Satpute et al.