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It’s all connected: modeling water potential and plant physiological processes

"As water potential is regarded the best indicator of plant water status, because it is the integrated result of above- and below-ground environmental conditions, it holds promise as a pivotal model variable to which other plant processes respond."
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Many parts of the world are already experiencing record drought. Global warming will increase drought intensity and frequency in the future. Drought has been shown to reduce yields of various crops from 30-92% depending upon the time of the onset of drought and stage of the crop.

Studying the flow and function of water in plants and their environment is the key to understanding the impact of drought.  Plant models are powerful tools that can capture and connect detailed knowledge of plant physiological processes. Despite the important role of water in plant function, many models do not simulate water hydraulics (i.e., movement).

Dr. Tom De Swaef, Research Associate at Flanders Research Institute for Agriculture, Fisheries and Food (ILVO) in Belgium and colleagues review the current and potential use of water hydraulics in computational models in a new article published by in silico Plants.

This article begins with an easy-to-understand introduction of the role of water potential in transporting water throughout the plant. Water potential is a measure of the free energy of water; it drives water flow from the soil, through the plant, and into the atmosphere. The introduction includes basic equations for calculating water potential in liquid and gaseous phases and factors that affect water potential (e.g., temperature and plant height). There is also an account of the usage of different terminology and units among scientific communities.

A diagram describing how water passes from soil into the roots and up the stem to leaves and flowers. The diagram is simple and bold and would not be mistaken for a real vascular plant.
Figure 1: Scheme of water flow and conductance through a plant.

The authors then dive into how water flow along the transpiration path is modeled by dividing the path into functional entities (see Figure 1):

  • soil to root – explains the basic water transport models and their evolution. The discussion incorporates the more recent development of capturing soil hydraulic conductivity by modeling the characteristics of the rhizosphere rather than bulk soil.
  • root epidermis to root xylem – describes the pathways for water transport and includes physiological factors that can affect the parameter values of hydraulic conductance and osmosis.
  • vertical inside xylem – depicts the role of the xylem and its composition. It details how the overestimation of hydraulic conductance occurs due to water transport occurring in the cell wall matrix and air bubbles within the xylem.
  • leaf xylem to sites of evaporation (leaf) – describes anatomical leaf traits that impact conductance and the use of modeling to determine environmental factors that affect hydraulic conductance.

Subsequently, the authors investigate how hydraulics are linked to other plant physiological processes in models like phloem transport, stomatal conductance, and plant growth.

Finally, the authors synthesize how water potential can serve as a central model variable that connects multiple eco-physiological mechanisms in plant models (see figure 2). Recent implementations of hydraulics in large-scale Terrestrial Biosphere Models improved their performance under water-limited conditions, while hydraulic features of recent detailed Functional-Structural Plant Models open new possibilities for dissecting complex traits for drought tolerance. These developments in models across scales deserve a critical appraisal to evaluate its potential for wider use in Functional-Structural Plant Models, and in crop systems models, where hydraulics are currently still absent.

Water potential connected to other variables including stomatal conductance, phloem transport and flower abortion.
Figure 2: Water potential as a central variable connecting plant physiological processes.

Then, they assess the potential of hydraulically based models for identifying interesting phenotypic traits for drought tolerance. Functional-Structural Plant Models and crop systems models both capture the effects of dynamic environmental conditions on plant physiological mechanisms underpinning the integrated plant response and resulting phenotype. Therefore, both have the potential to be used to identify phenotypic traits for drought tolerance. However, this requires an accurate representation of relevant physiological mechanisms affecting hydraulics in the model, as previously described.

READ THE ARTICLE:

Tom De Swaef, Olivier Pieters, Simon Appeltans, Irene Borra-Serrano, Willem Coudron, Valentin Couvreur, Sarah Garré, Peter Lootens, Bart Nicolaï, Leroi Pols, Clément Saint Cast, Jakub Šalagovič, Maxime Van Haeverbeke, Michiel Stock, Francis wyffels, On the pivotal role of water potential to model plant physiological processes, in silico Plants, 2022;, diab038, https://doi.org/10.1093/insilicoplants/diab038


This manuscript is part of in silico Plant’s Functional Structural Plant Model special issue.

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