On the pivotal role of water potential to model plant physiological processes

Abstract

Water potential explains water transport in the Soil-Plant-Atmosphere Continuum (SPAC), and is gaining interest as connecting variable between ‘pedo-, bio- and atmosphere’. It is primarily used to simulate hydraulics in the SPAC, and is thus essential for studying drought effects. Recent implementations of hydraulics in large-scale Terrestrial Biosphere Models (TBMs) improved their performance under water-limited conditions, while hydraulic features of recent detailed Functional-Structural Plant Models (FSPMs) 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 FSPMs, but also in crop systems models (CSMs), where hydraulics are currently still absent. After refreshing the physical basis, we first address models where water potential is primarily used for describing water transport along the transpiration pathway from the soil to the leaves, through the roots, the xylem and the leaf mesophyll. Then, we highlight models for three ecophysiological processes, which have well-recognised links to water potential: phloem transport, stomatal conductance and organ growth. We identify water potential as the bridge between soil, root and shoot models, as the physiological variable integrating below- and above-ground abiotic drivers, but also as the link between water status and growth. Models making these connections enable identifying crucial traits for ecosystem resilience to drought and for breeding towards improved drought tolerance in crops. Including hydraulics often increases model complexity, and thus requires experimental data on soil and plant hydraulics. Nevertheless, modelling hydraulics is insightful at different scales (FSPMs, CSMs and TBMs).

Leveraging plant physiological dynamics using physical reservoir computing

“…Leaf thickness is an interesting trait to monitor since it varies rapidly. Leaf thickness is often employed as a proxy for the dynamic plant water balance, which is influenced by variations in environmental variables such as light exposure, temperature, relative humidity and plant-specific factors such as age 33 – 35 . Consequently, it is a highly informative measure on the status of the plant.…”

“…Moreover, strong couplings exist between plant-processes such as stomatal conductivity, transpiration rate, photosynthesis and leaf thickness due to common driving elements (e.g. water potential and light availability) 35 . The observation that domain-specific computers are better at solving problems within their domain has already been reported in literature.…”

“…While short-term leaf thickness variations are a good proxy for plant water status dynamics, there are many more unknown factors such as hormones, metabolism, nutrient and carbon dynamics. These are also part of the reservoir but not directly quantifiable using leaf thickness measurements, although correlations will exist with leaf thickness because merely all plant processes are impacted by the plant’s water status 35 , 50 .…”

In silico evidence for the utility of parsimonious root phenotypes for improved vegetative growth and carbon sequestration under drought

“…Plant water status reflects the synchronized response of the plant to soil water availability and atmospheric demand ( Silva and Lambers, 2021 ). Shoot water loss is driven by atmospheric demand together with leaf area, stomatal conductance, and intrinsic water uptake capacity of the plant ( De Swaef et al., 2022 ). On the other hand, soil properties and root architecture largely determine the water availability to the plant.…”

In silicoevidence for the utility of parsimonious root phenotypes for improved vegetative growth and carbon sequestration under drought

“…From the paradigm of the soil-plant-atmosphere continuum, the plant water status reflects the synchronized response of the plant to soil water availability and atmospheric demand Silva and Lambers (2021). Shoot water loss is driven by atmospheric demand together with leaf area, stomatal conductance, and intrinsic water uptake capacity of the plant De Swaef et al (2022). On other hand, soil properties and root architecture largely determine the water availability to the plant.…”