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Abstract
Root hydraulic properties play a central role in the global water cycle, in agricultural
systems productivity, and in ecosystem survival as they impact the canopy water supply.
However, the existing experimental methods to quantify root hydraulic conductivities,
such as the root pressure probing, are particularly challenging, and their applicability
to thin roots and small root segments is limited. Therefore, there is a gap in methods
enabling easy estimations of root hydraulic conductivities in diverse root types.
Here, we present a new pipeline to quickly estimate root hydraulic conductivities
across different root types, at high resolution along root axes. Shortly, free-hand
root cross-sections were used to extract a selected number of key anatomical traits.
We used these traits to parametrize the Generator of Root Anatomy in R (GRANAR) model
to simulate root anatomical networks. Finally, we used these generated anatomical
networks within the Model of Explicit Cross-section Hydraulic Anatomy (MECHA) to compute
an estimation of the root axial and radial hydraulic conductivities (k x and k r ,
respectively). Using this combination of anatomical data and computational models,
we were able to create a root hydraulic conductivity atlas at the root system level,
for 14-day-old pot-grown Zea mays (maize) plants of the var. B73. The altas highlights
the significant functional variations along and between different root types. For
instance, predicted variations of radial conductivity along the root axis were strongly
dependent on the maturation stage of hydrophobic barriers. The same was also true
for the maturation rates of the metaxylem vessels. Differences in anatomical traits
along and across root types generated substantial variations in radial and axial conductivities
estimated with our novel approach. Our methodological pipeline combines anatomical
data and computational models to turn root cross-section images into a detailed hydraulic
atlas. It is an inexpensive, fast, and easily applicable investigation tool for root
hydraulics that complements existing complex experimental methods. It opens the way
to high-throughput studies on the functional importance of root types in plant hydraulics,
especially if combined with novel phenotyping techniques such as laser ablation tomography.