Mathieu Javaux

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus , showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in-situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus, showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in-situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus, showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in-situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus, showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in-situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus, showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

Knowledge about plant water stress regulation mechanisms (e.g., plant stem capacitance) from in-situ observation is crucial for the study and modeling of plant root water uptake (RWU). We present a proof of concept and a first application of a simple method for online, minimally invasive monitoring of the water stable isotopic composition of sap xylem water of Helianthus annuus (sunflower) by inserting a sampling tube connected to a laser spectrometer in the plant stem. After careful calibration of our method, we applied it successfully to individual sunflower plants grown in soil columns. We followed the dynamics in stem water isotopic composition in response to changing light intensity and to depth-specific, isotopically labeled water pulses. We further establish that these isotopic dynamics matched changes in RWU profiles monitored simultaneously, independently, and non-destructively by the Soil Water Profiler. We finally highlight from modeling exercises the significance of the role of plant stem capacitance: water exchanges between xylem and stem non-conducting tissues were estimated to amount to about one sixth of RWU of Helianthus annuus, showing that the stem itself can be expected to be a quickly accessible reservoir of water for transpiration, very similar to what is found in trees.

The objective of this study is to investigate experimentally how plants adjust their structural and functional properties when facing soil water heterogeneity from the plant down to the organ scales. We developed a novel rhizotron platform, each rhizotron equipped with 9 hydraulically isolated compartments, wherein constant spatial patterns of local soil water potential can be imposed while monitoring water consumption and root development. In the validation experiment, maize plants (cv. B104) were grown under constant and homogeneous water potential in this rhizotron platform for four weeks, before entering a fifth week in which different levels of water potential were imposed. The desired local soil water potentials were successfully applied and adjusted. The local water consumption and root morphological trails were monitored in real time, indicating that root water uptake and root elongation correlate with root age and local soil moisture. At the whole-plant scale, more negative soil water potentials resulted in a lower cumulative water uptake, while at the local scale, cumulative water uptake within individual compartments increased more rapidly as root length within the same compartment increased, indicating a direct coupling between local root development and local water extraction. These observations highlight a strong spatial-temporal linkage between root trails and soil water conditions. Together, the validated rhizotron platform enables root plasticity studies by establish a quantitative and dynamic measurements for soil–root hydraulic interactions at the plant and organ scale, providing a promising platform for future studies exploring how maize plants respond to spatial and temporal heterogeneity in soil water environments.

Land cover changes exert growing pressure on soils and can modify their physical structure and hydraulic behaviour. While the influence of land cover on erosion, compaction, and biological activity in the upper 30 cm is well documented, much less is known about how far these effects extend into deeper horizons. Here, we analyse depth-dependent variations in structural and hydraulic properties for soils of comparable texture under cropland, grassland, and forest. We used the EU-HYDI database, comprising 6,014 profiles and over 18,000 samples across Europe (36% with LUCAS land cover information). Samples were grouped by texture classes (using a modified version of the HYPRES texture triangle) and land cover independently of soil profile. For each texture X land cover combination, we fitted generalized additive models (GAMs) with depth, including random effects for data source to account for heterogeneity in analytical methods and sampling protocols. Results reveal significant differences in bulk density and θsat up to 60 cm, with consistent patterns (cropland > grassland > forest for bulk density; cropland < grassland < forest for θsat). These results show that land cover impacts are not restricted to the topsoil, highlight the lack of subsoil data, particularly for fine-textured soils and forested sites and underscores the importance of harmonized measurement procedures to improve comparability in soil hydrological studies.

DeepHorizon is a Horizon Europe Soil Mission project which aims to uncover hidden potential of European subsoils, an overlooked but vital component in soil functioning. Knowledge of subsoil dynamics, functions and degradation remains limited, and the pressure of unsustainable land management practices (LMPs) and climate change are increasing. To address this, DeepHorizon is leveraging multi-disciplinary collaborations across 19 international institutions to i) map subsoil properties, ii) identify sustainable subsoil management practices, and iii) develop and refine user-oriented tools to monitor and improve subsoil health.The initial sampling campaign is underway, with 19 of our 40 sites sampled, which will be completed by the end of Autumn this year. Excavating a soil trench up to 2-meters provides comprehensive physical, chemical and biological data to capture subsoil properties including soil texture, pH, Carbon, Nitrogen and other nutrients, X-ray CT, hydraulics, root length density, fauna, microbiology and more. These data will contribute to a better representation of subsoils in existing databases and calibrate two process-based models to improve representation of subsoil functions.These models will be validated across 100+ test sites and 3 regional case-study areas (CSA), then adapted to suit the needs of end-users through farmer- and manager-friendly tools. The project will also assess the socio-economic impact and environmental trade-offs of LMPs to generate policy recommendations and incentives to propose the sustainable management and restoration of European subsoil.To ensure widespread impact, DeepHorizon engages land managers, researchers and policymakers through Community of Practice (CoP) and targeted outreach and communication activities. To facilitate the work planned on future test sites and case study areas, we are looking for constructive feedback, synergies, and collaborations that may be available across existing projects, institutions or individuals.

Stony soils are very common in non-agricultural landscapes. Yet, characterizing the hydraulic properties of stony subsoil is necessary but technically complex.In this study, we aim to improve the characterization of stony subsoils by addressing two critical aspects: (i) the estimation of coarse fragment content and (ii) the water retention of stones. Both factors potentially influence plant available water capacity - a key input for many hydrological models - and its uncertainty, yet they are rarely quantified in deep horizons.Our methodology involved eleven forest sites in Wallonia (Belgium), where soil pits were excavated down to 2 m depth to capture the vertical variability of soil texture, stoniness, hydraulic properties. Coarse fragment content was assessed by horizon using four approaches: two in situ methods and two laboratory-based methods applied to samples of different sizes. Additionally, we carry out measurements on stones to measure available water between field capacity and wilting point.Preliminary results underline the importance of adapting soil sampling volume and method to the degree of soil heterogeneity to quantify stone water availability at the profile scale. Our results also indicate that certain rock types can hold up to 15 % of their volume of plant available water, challenging the common assumption that their contribution is negligible.