A root hydraulic properties database: the link between experimental data and functional-structural models

Root water uptake is a central component in the modulation of water transport in the soil-plant-atmosphere continuum. The mechanistic description of this process, based on root hydraulics, is needed for improving predictions of water fluxes at plant, field or regional scales, and for increasing our understanding of the environmental conditions and vegetation properties affecting it. Functional-structural models can be used for this purpose, but they depend on the availability of accurate data on root hydraulic properties for their parametrization. 

Here, we present an open access root hydraulic properties database obtained from an extensive literature review of more than 200 studies published between 1973–2022. This includes measurements of the radial conductivity and the axial conductance of root segments and individual roots, as well as of the resulting conductance of the whole root system for multiple species, plant functional types (PFT’s) and experimental treatments. To our knowledge, this is the most extensive root hydraulic properties database that has been compiled.

The database shows a very large range of variation in reported root hydraulic properties, which cannot be explained by systematic differences among PFT’s or species, alone, but rather by factors such as root system age, experimental treatments or the driving force used for measurement (hydrostatic or osmotic). Based on these observations, we used the functional-structural model CPlantBox to explore the relationship between root system age and whole root system conductance in more detail, using crop species as an example. For this, both the data needed for model parametrization (hydraulic properties of root segments) and validation (root system conductance) were extracted from the database. The results indicate a decrease in the total conductance per unit root surface area at later stages of development, which could be associated with a larger proportion of less conductive old root tissues.

This analysis exemplifies the importance of the root hydraulic database in two fronts: (1) it serves as a link between experimental data and functional-structural models; and (2) it facilitates the mechanistic description of the factors affecting root hydraulic properties across species and under contrasting environmental conditions.