Mucilage exudation facilitates root water uptake in dry soils

2014 ◽  
Vol 41 (11) ◽  
pp. 1129 ◽  
Author(s):  
Mutez A. Ahmed ◽  
Eva Kroener ◽  
Maire Holz ◽  
Mohsen Zarebanadkouki ◽  
Andrea Carminati
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Water Uptake ◽  
Root Water Uptake ◽  
Root Surface ◽  
Pressure Probe ◽  
Root Pressure ◽  
Plant Trait ◽  
Suction Cup ◽  
Relaxation Curves

As plant roots take up water and the soil dries, water depletion is expected to occur in the rhizosphere. However, recent experiments showed that the rhizosphere was wetter than the bulk soil during root water uptake. We hypothesise that the increased water content in the rhizosphere was caused by mucilage exuded by roots. It is probably that the higher water content in the rhizosphere results in higher hydraulic conductivity of the root–soil interface. In this case, mucilage exudation would favour the uptake of water in dry soils. To test this hypothesis, we covered a suction cup, referred to as an artificial root, with mucilage. We placed it in soil with a water content of 0.03 cm3 cm–3, and used the root pressure probe technique to measure the hydraulic conductivity of the root–soil continuum. The results were compared with measurements with roots not covered with mucilage. The root pressure relaxation curves were fitted with a model of root water uptake including rhizosphere dynamics. The results demonstrated that when mucilage is added to the root surface, it keeps the soil near the roots wet and hydraulically well conductive, facilitating the water flow from dry soils towards the root surface. Mucilage exudation seems to be an optimal plant trait that favours the capture of water when water is scarce.

scholarly journals Modelling the Impact on Root Water Uptake and Solute Return Flow of Different Drip Irrigation Regimes with Brackish Water

Water ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 425 ◽  
Author(s):  
Fairouz Slama ◽  
Nessrine Zemni ◽  
Fethi Bouksila ◽  
Roberto De Mascellis ◽  
Rachida Bouhlila
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Water Uptake ◽  
Brackish Water ◽  
Deficit Irrigation ◽  
Root Zone ◽  
Root Water Uptake ◽  
Return Flows ◽  
Semi Arid

Water scarcity and quality degradation represent real threats to economic, social, and environmental development of arid and semi-arid regions. Drip irrigation associated to Deficit Irrigation (DI) has been investigated as a water saving technique. Yet its environmental impacts on soil and groundwater need to be gone into in depth especially when using brackish irrigation water. Soil water content and salinity were monitored in a fully drip irrigated potato plot with brackish water (4.45 dSm−1) in semi-arid Tunisia. The HYDRUS-1D model was used to investigate the effects of different irrigation regimes (deficit irrigation (T1R, 70% ETc), full irrigation (T2R, 100% ETc), and farmer’s schedule (T3R, 237% ETc) on root water uptake, root zone salinity, and solute return flows to groundwater. The simulated values of soil water content (θ) and electrical conductivity of soil solution (ECsw) were in good agreement with the observation values, as indicated by mean RMSE values (≤0.008 m3·m−3, and ≤0.28 dSm−1 for soil water content and ECsw respectively). The results of the different simulation treatments showed that relative yield accounted for 54%, 70%, and 85.5% of the potential maximal value when both water and solute stress were considered for deficit, full. and farmer’s irrigation, respectively. Root zone salinity was the lowest and root water uptake was the same with and without solute stress for the treatment corresponding to the farmer’s irrigation schedule (273% ETc). Solute return flows reaching the groundwater were the highest for T3R after two subsequent rainfall seasons. Beyond the water efficiency of DI with brackish water, long term studies need to focus on its impact on soil and groundwater salinization risks under changing climate conditions.

Root hairs bridge the gap between roots and soil water

2020 ◽  
Author(s):  
Patrick Duddek ◽  
Mutez Ahmed ◽  
Mohsen Zarebanadkouki ◽  
Nicolai Koebernick ◽  
Goran Lovric ◽  
...  
Keyword(s):  
Water Uptake ◽  
Contact Area ◽  
Geodesic Distance ◽  
Root Hairs ◽  
Root Water Uptake ◽  
Root Surface ◽  
Particle Packing ◽  
Biophysical Properties ◽  
Soil Matrix ◽  
Water Potentials

<p>Although 40% of total terrestrial precipitation transits the rhizosphere, there is still substantive lack of understanding of the rhizosphere biophysical properties and their impact on root water uptake. Our hypothesis is that roots are capable of altering the biophysical properties of the rhizosphere and hereby facilitating root water uptake. In particular, we expect that root hairs maintain the hydraulic contact between roots and soil at low water potentials. We have recently shown that root hairs facilitate root water uptake in dry soils at high transpiration rates. Our explanation was that root hairs extend the effective root radius decreasing the flow velocity at the root surface and hence the drop in matric potential across the rhizosphere.</p><p>To test this hypothesis, we used synchrotron X-ray CT to image the distribution of root hairs in soils. The experiments were conducted with two maize genotypes (with and without root hairs) grown in two soil textures (loam vs sand). Segmenting the different domains within the high-resolution images enabled us to quantify the contact area of the root surface and root hairs with the soil matrix at different water potentials. Furthermore, we calculated the geodesic distance between the root and the soil matrix as a proxy of the accessibility of water to the root.</p><p>The results show that root hairs increase the total root surface by approx. 30% and the contact area with the soil matrix by approx. 40%. Furthermore, the average distance from the soil to the root surface decreases by approx. 40% due to hairs, which is the effect of root hairs preferentially growing through macropores. In summary, root hairs not only increase the root surface and the root-soil contact area, but also bridge the air-filled pores between the root epidermis and the soil matrix, thus facilitating the extraction of water.  On top of that, the segmented CT images are also the basis for image-based models aiming at quantifying root water uptake and the effect of root hairs.</p><p> </p><p> </p><p>References</p><ul><li>(1) Koebernick N, Daly KR, Keyes SD, et al. 2019. Imaging microstructure of the barley rhizosphere: particle packing and root hair influences. New Phytologist 221, 1878–1889.</li> <li>(2) Carminati A, Benard P, Ahmed MA, Zarebanadkouki M. 2017. Liquid bridges at the root-soil interface. Plant and Soil 417, 1–15.</li> </ul><p> </p>

Estimation of root water uptake parameters by inverse modeling with soil water content data

2003 ◽  
Vol 39 (11) ◽  
Author(s):  
F. Hupet ◽  
S. Lambot ◽  
R. A. Feddes ◽  
J. C. van Dam ◽  
M. Vanclooster
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Water Uptake ◽  
Inverse Modeling ◽  
Root Water Uptake

scholarly journals On the identification of macroscopic root water uptake parameters from soil water content observations

2002 ◽  
Vol 38 (12) ◽  
pp. 36-1-36-14 ◽  
Author(s):  
F. Hupet ◽  
S. Lambot ◽  
M. Javaux ◽  
M. Vanclooster
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Water Uptake ◽  
Root Water Uptake

scholarly journals Using measured soil water contents to estimate evapotranspiration and root water uptake profiles – a comparative study

2015 ◽  
Vol 19 (1) ◽  
pp. 409-425 ◽  
Author(s):  
M. Guderle ◽  
A. Hildebrandt
Keyword(s):  
Time Series ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Water Uptake ◽  
Root Water Uptake ◽  
Performance Criteria ◽  
Sensor Calibration ◽  
Vertical Flow ◽  
Sink Term

Abstract. Understanding the role of plants in soil water relations, and thus ecosystem functioning, requires information about root water uptake. We evaluated four different complex water balance methods to estimate sink term patterns and evapotranspiration directly from soil moisture measurements. We tested four methods. The first two take the difference between two measurement intervals as evapotranspiration, thus neglecting vertical flow. The third uses regression on the soil water content time series and differences between day and night to account for vertical flow. The fourth accounts for vertical flow using a numerical model and iteratively solves for the sink term. None of these methods requires any a priori information of root distribution parameters or evapotranspiration, which is an advantage compared to common root water uptake models. To test the methods, a synthetic experiment with numerical simulations for a grassland ecosystem was conducted. Additionally, the time series were perturbed to simulate common sensor errors, like those due to measurement precision and inaccurate sensor calibration. We tested each method for a range of measurement frequencies and applied performance criteria to evaluate the suitability of each method. In general, we show that methods accounting for vertical flow predict evapotranspiration and the sink term distribution more accurately than the simpler approaches. Under consideration of possible measurement uncertainties, the method based on regression and differentiating between day and night cycles leads to the best and most robust estimation of sink term patterns. It is thus an alternative to more complex inverse numerical methods. This study demonstrates that highly resolved (temporally and spatially) soil water content measurements may be used to estimate the sink term profiles when the appropriate approach is used.

scholarly journals Comparison of root water uptake models in simulating CO<sub>2</sub> and H<sub>2</sub>O fluxes and growth of wheat

2020 ◽  
Vol 24 (10) ◽  
pp. 4943-4969
Author(s):  
Thuy Huu Nguyen ◽  
Matthias Langensiepen ◽  
Jan Vanderborght ◽  
Hubert Hüging ◽  
Cho Miltin Mboh ◽  
...  
Keyword(s):  
Stomatal Conductance ◽  
Root Growth ◽  
Water Content ◽  
Soil Water ◽  
Water Uptake ◽  
Coupled Model ◽  
Hydraulic Conductance ◽  
Root Water Uptake ◽  
Whole Plant ◽  
Hydraulic Signaling

Abstract. Stomatal regulation and whole plant hydraulic signaling affect water fluxes and stress in plants. Land surface models and crop models use a coupled photosynthesis–stomatal conductance modeling approach. Those models estimate the effect of soil water stress on stomatal conductance directly from soil water content or soil hydraulic potential without explicit representation of hydraulic signals between the soil and stomata. In order to explicitly represent stomatal regulation by soil water status as a function of the hydraulic signal and its relation to the whole plant hydraulic conductance, we coupled the crop model LINTULCC2 and the root growth model SLIMROOT with Couvreur's root water uptake model (RWU) and the HILLFLOW soil water balance model. Since plant hydraulic conductance depends on the plant development, this model coupling represents a two-way coupling between growth and plant hydraulics. To evaluate the advantage of considering plant hydraulic conductance and hydraulic signaling, we compared the performance of this newly coupled model with another commonly used approach that relates root water uptake and plant stress directly to the root zone water hydraulic potential (HILLFLOW with Feddes' RWU model). Simulations were compared with gas flux measurements and crop growth data from a wheat crop grown under three water supply regimes (sheltered, rainfed, and irrigated) and two soil types (stony and silty) in western Germany in 2016. The two models showed a relatively similar performance in the simulation of dry matter, leaf area index (LAI), root growth, RWU, gross assimilation rate, and soil water content. The Feddes model predicts more stress and less growth in the silty soil than in the stony soil, which is opposite to the observed growth. The Couvreur model better represents the difference in growth between the two soils and the different treatments. The newly coupled model (HILLFLOW–Couvreur's RWU–SLIMROOT–LINTULCC2) was also able to simulate the dynamics and magnitude of whole plant hydraulic conductance over the growing season. This demonstrates the importance of two-way feedbacks between growth and root water uptake for predicting the crop response to different soil water conditions in different soils. Our results suggest that a better representation of the effects of soil characteristics on root growth is needed for reliable estimations of root hydraulic conductance and gas fluxes, particularly in heterogeneous fields. The newly coupled soil–plant model marks a promising approach but requires further testing for other scenarios regarding crops, soil, and climate.

The plant water pump: why water flows uphill of water potential gradients in a root hydraulic anatomy model

2021 ◽  
Author(s):  
Valentin Couvreur ◽  
Adrien Heymans ◽  
Guillaume Lobet ◽  
Malcolm Bennett ◽  
Xavier Draye
Keyword(s):  
Water Potential ◽  
Water Uptake ◽  
Driving Force ◽  
Xylem Sap ◽  
Potential Gradient ◽  
Root Water Uptake ◽  
Total Water ◽  
Root Pressure ◽  
Hydraulic Network ◽  
Osmotic Potentials

&lt;p&gt;Guttation is the exudation of xylem sap from vascular plant leaves. This process is particularly interesting because in its configuration root water uptake occurs against the hydrostatic pressure driving force. Hence, it emphasizes the contribution of another driving force that lifts water in plants: the osmotic potential gradient.&lt;/p&gt;&lt;p&gt;The current paradigm of root water uptake explains that, due to the endodermal apoplastic barrier, water flows across root radius from the same principles as through selective membranes: driven by the total water potential gradient. This theory relies on the idea that during guttation, osmolites loaded in xylem vessels decrease xylem total water potential, making it more negative than the total soil water potential, and generating water inflow by osmosis as in an osmometer.&lt;/p&gt;&lt;p&gt;However, this theory fails at explaining experiments in which guttation occurs without sufficient solute loading in root xylem of maize (Enns et al., 1998; Enns et al., 2000) and arrowleaf saltbush (Bai et al., 2007) among others; studies concluding that experimental observations &amp;#8220;could not be explained with the current theories in plant physiology&amp;#8221;. Such flow rates towards combined increasing pressure potentials and increasing osmotic potentials between separate apoplastic compartments would necessitate an effective root radial conductivity that is negative; a mind bender.&lt;/p&gt;&lt;p&gt;What piece of hydraulic network would make it possible for water to flow against the total water potential driving force?&lt;/p&gt;&lt;p&gt;We implemented Steudle&amp;#8217;s composite water transport model in the explicit root cross-section anatomical hydraulic network MECHA (Couvreur et al., 2018). All apoplastic, transmembrane and symplastic pathways are interconnected in the network. The results show that while root radial conductivity is particularly sensitive to cell membrane permeability, the combination of conductive plasmodesmata and increased dilution of protoplast osmotic potentials inwards is a key to explain root water flow towards increasing total potentials. A triple cell theory is suggested as new paradigm of root radial flow.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Bai X-F, Zhu J-J, Zhang P, Wang Y-H, Yang L-Q, Zhang L (2007) Na+ and Water Uptake in Relation to the Radial Reflection Coefficient of Root in Arrowleaf Saltbush Under Salt Stress. Journal of Integrative Plant Biology 49: 1334-1340&lt;/p&gt;&lt;p&gt;Couvreur V, Faget M, Lobet G, Javaux M, Chaumont F, Draye X (2018) Going with the Flow: Multiscale Insights into the Composite Nature of Water Transport in Roots. Plant Physiology 178: 1689-1703&lt;/p&gt;&lt;p&gt;Enns LC, Canny MJ, McCully ME (2000) An investigation of the role of solutes in the xylem sap and in the xylem parenchyma as the source of root pressure. Protoplasma 211: 183-197&lt;/p&gt;&lt;p&gt;Enns LC, McCully ME, Canny MJ (1998) Solute concentrations in xylem sap along vessels of maize primary roots at high root pressure. J. Exp. Bot. 49: 1539-1544&lt;/p&gt;

Root bio-hydro-mechanical reinforcement of unsaturated vegetated soil: experiments and modelling

2021 ◽  
Author(s):  
Anthony Leung ◽  
Davide Boldrin ◽  
Ali Akbar Karimzadeh ◽  
Zhaoyi Wu ◽  
Suriya Ganesan
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Water Retention ◽  
Water Regime ◽  
Biomechanical Properties ◽  
Root Water Uptake ◽  
Water Retention Curve ◽  
Retention Curve ◽  
Soil Bioengineering ◽  
Induced Changes

&lt;p&gt;Plant roots affect soil water regime through root-water uptake upon transpiration. This process induces soil matric suction, which affects soil hydraulic conductivity, soil shear strength and hence shallow soil stability. This is referred to as plant hydrological reinforcement in the soil bioengineering application. Recent experimental evidence put forward by the authors has demonstrated that plant hydrological reinforcement should not be exclusively limited to the effects of root-water uptake and plant transpiration. The presentation will provide some new evidence of other potential aspects of plant hydrological reinforcement, namely (1) root-induced changes in soil hydraulic properties, (2) root water-dependent bio-hydro-mechanical properties. In aspect (1), laboratory test results on how root growth dynamic alter the soil pore size distribution and hence affect both the soil water retention curve and hydraulic conductivity will be presented. To highlight the effects of these root-induced changes in soil properties on slope water regime and slope stability, numerical simulation employing a dual-permeability water transport model in unsaturated rooted soil will be discussed. In aspect (2), a new concept, hysteretic root water retention curve (relationship between root water content and root water potential), will be introduced with support of some preliminary data. How root water retention affects the root biomechanical properties including not only tensile strength and Young&amp;#8217;s modulus that have received wide attention in the soil bioengineering literature but also breakage strain will be presented. New data will be provided in order to attempt to use root water content to explain the large variability of biomechanical properties observed in the literature.&lt;/p&gt;

Functional-structural modelling of root water uptake based on measured MRI images of root systems

2020 ◽  
Author(s):  
Tobias Selzner ◽  
Magdalena Landl ◽  
Andreas Pohlmeier ◽  
Daniel Leitner ◽  
Jan Vanderborght ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Drought Tolerance ◽  
Soil Water ◽  
Water Uptake ◽  
Root Architecture ◽  
Soil Water Potential ◽  
Computational Cost ◽  
Root Water Uptake ◽  
Extreme Weather Events ◽  
Richards Equation

&lt;p&gt;In the course of climate change, the occurrence of extreme weather events is expected to increase. Drought tolerance of crops and careful irrigation management are becoming key factors for global food security and the sustainable resource use of water in agriculture. Root water uptake plays a vital role in drought tolerance. It is influenced by root architecture, plant and soil water status and their respective hydraulic properties. Models of said factors aid in organizing the current state of knowledge and enable a deeper understanding of their respective influence on crop performance. Water uptake by roots leads to a decrease in soil moisture and may cause the formation of soil water potential gradients between the bulk soil and the soil-root interface. Although the Richards equation in theory takes these gradients into account, a very fine discretization of the soil domain is necessary to capture these gradients in simulations. However, especially during drought stress, the drop in hydraulic conductivity in the rhizosphere could have a major impact on the overall water uptake of the root system. In order to investigate computationally feasible alternative approaches for simulations with source terms that take these hydraulic conductivity drops into account, we conducted experiments with lupine plants. The root architecture of the growing plants was measured several times using an MRI. Subsequently, these MRI images were used in a holobench for manual tracing of the roots. We were able to mimic the root growth between the measurement dates using linear interpolation. In addition to root architecture, soil water contents and transpiration rates were monitored. We then used this data to systematically compare the computational effort of different approaches to consider the hydraulic conductivity drop near roots in terms of accuracy and computational cost. Eventually we aim at using these results to improve existing root water uptake models for the presence of hydraulic conductivity drops in the rhizosphere in an efficient and accurate way.&lt;/p&gt;

Effect of Local Soil Hydraulic Conductivity Drop Using a Three-Dimensional Root Water Uptake Model

2008 ◽  
Vol 7 (3) ◽  
pp. 1089-1098 ◽  
Author(s):  
Tom Schröder ◽  
Mathieu Javaux ◽  
Jan Vanderborght ◽  
Bernd Körfgen ◽  
Harry Vereecken
Keyword(s):  
Hydraulic Conductivity ◽  
Water Uptake ◽  
Three Dimensional ◽  
Root Water Uptake ◽  
Soil Hydraulic Conductivity ◽  
Local Soil ◽  
Soil Hydraulic
Sign in / Sign up

Export Citation Format

Share Document