scholarly journals Implementing small scale processes at the soil-plant interface – the role of root architectures for calculating root water uptake profiles

2010 ◽  
Vol 14 (2) ◽  
pp. 279-289 ◽  
Author(s):  
C. L. Schneider ◽  
S. Attinger ◽  
J.-O. Delfs ◽  
A. Hildebrandt
Keyword(s):  
Soil Water ◽  
Water Flow ◽  
Water Uptake ◽  
Soil Water Potential ◽  
Root Systems ◽  
Root Water Uptake ◽  
Bulk Soil ◽  
Small Scale ◽  
Sink Term

Abstract. In this paper, we present a stand alone root water uptake model called aRoot, which calculates the sink term for any bulk soil water flow model taking into account water flow within and around a root network. The boundary conditions for the model are the atmospheric water demand and the bulk soil water content. The variable determining the plant regulation for water uptake is the soil water potential at the soil-root interface. In the current version, we present an implementation of aRoot coupled to a 3-D Richards model. The coupled model is applied to investigate the role of root architecture on the spatial distribution of root water uptake. For this, we modeled root water uptake for an ensemble (50 realizations) of root systems generated for the same species (one month old Sorghum). The investigation was divided into two Scenarios for aRoot, one with comparatively high (A) and one with low (B) root radial resistance. We compared the results of both aRoot Scenarios with root water uptake calculated using the traditional Feddes model. The vertical rooting density profiles of the generated root systems were similar. In contrast the vertical water uptake profiles differed considerably between individuals, and more so for Scenario B than A. Also, limitation of water uptake occurred at different bulk soil moisture for different modeled individuals, in particular for Scenario A. Moreover, the aRoot model simulations show a redistribution of water uptake from more densely to less densely rooted layers with time. This behavior is in agreement with observation, but was not reproduced by the Feddes model.

scholarly journals Implementing small scale processes at the soil-plant interface – the role of root architectures for calculating root water uptake profiles

2009 ◽  
Vol 6 (3) ◽  
pp. 4233-4264 ◽  
Author(s):  
C. L. Schneider ◽  
S. Attinger ◽  
J.-O. Delfs ◽  
A. Hildebrandt
Keyword(s):  
Soil Water ◽  
Water Flow ◽  
Water Uptake ◽  
Soil Water Potential ◽  
Root Systems ◽  
Root Water Uptake ◽  
Bulk Soil ◽  
Small Scale ◽  
Sink Term

Abstract. In this paper, we present a stand alone root water uptake model called aRoot, which calculates the sink term for any bulk soil water flow model taking into account water flow within and around a root network. The boundary conditions for the model are the atmospheric water demand and the bulk soil water content. The variable determining the plant regulation for water uptake is the soil water potential at the soil-root interface. In the current version, we present an implementation of aRoot coupled to a 3-D Richards model. The coupled model is applied to investigate the role of root architecture on the spatial distribution of root water uptake. For this, we modeled root water uptake for an ensemble (50 realizations) of root systems generated for the same species (one month old Sorghum). The investigation was divided into two Scenarios for aRoot, one with comparatively high (A) and one with low (B) root radial resistance. We compared the results of both aRoot Scenarios with root water uptake calculated using the traditional Feddes model. The vertical rooting density profiles of the generated root systems were similar. In contrast the vertical water uptake profiles differed considerably between individuals, and more so for Scenario B than A. Also, limitation of water uptake occurred at different bulk soil moisture for different modeled individuals, in particular for Scenario A. Moreover, the aRoot model simulations show a redistribution of water uptake from more densely to less densely rooted layers with time. This behavior is in agreement with observation, but was not reproduced by the Feddes model.

How to scale root water uptake from root scale to stands and beyond – a theoretical framework, practical lessons, and next steps

2020 ◽  
Author(s):  
Martin Bouda ◽  
Jan Vanderborght ◽  
Valentin Couvreur ◽  
Félicien Meunier ◽  
Mathieu Javaux
Keyword(s):  
Soil Moisture ◽  
Soil Water ◽  
Water Flow ◽  
Water Uptake ◽  
Root Systems ◽  
Root Water Uptake ◽  
Discretization Error ◽  
Persistent Problem ◽  
Plant Hydraulics ◽  
Soil Moisture Heterogeneity

<p>Estimating plant uptake of soil water has been a persistent problem in process-based earth system models (ESMs). Initially ignored altogether, plant access to soil water was long modelled with heuristic approaches at large scales. These formulations are currently being replaced as ESMs begin to incorporate more detailed plant hydraulics schemes based on the soil-plant-atmosphere continuum concept. While the new schemes greatly improve mechanistic description of above-ground plant hydraulics, they have given rise to various issues belowground, from excessive hydraulic redistribution to numerical instability. As detailed 3D descriptions of root systems and water flow equations on the soil-root domain have been established, the key challenge is how to scale them up to relevant scales, reducing computational cost to a trivial level without loss of accuracy.</p><p>Here, we set out a mathematical framework that incorporates recent advances in this area and allows us to relate them to each other. Comparing and contrasting different models, formulated in a novel matrix form of the water flow problem in the root system, allows us to make inferences about their suitability for use in upscaling. We are able to show how to avoid discretization error in the upscaled root scheme, as well as which upscaling method offers full generality, and which yields the computationally simplest forms. These theoretical results are fully supported by numerical simulations of fully explicit 3D root systems and their upscaled versions. Improved performance of the upscaled models is also demonstrated in an application to field data from the Wind River Crane flux tower site (reduced model bias, root mean squared error, and increased robustness of fitted parameters).</p><p>Root water uptake equations can now be scaled up without discretization error for arbitrary root systems. The chief remaining source of error is soil moisture heterogeneity within discretized soil elements where it is assumed uniform by any given model (e.g. within each vertical layer). The main task for future work thus becomes to achieve a correspondingly accurate description for soil moisture heterogeneity. Some of the upscaling approaches compared here offer hints at potential next steps in this direction.</p>

SIMULATING SOIL WATER FLOW WITH ROOT-WATER-UPTAKE APPLYING AN INVERSE METHOD

Soil Science ◽  
2004 ◽  
Vol 169 (1) ◽  
pp. 13-24 ◽  
Author(s):  
Qiang Zuo ◽  
Lei Meng ◽  
Renduo Zhang
Keyword(s):  
Soil Water ◽  
Water Flow ◽  
Water Uptake ◽  
Inverse Method ◽  
Root Water Uptake ◽  
Soil Water Flow

scholarly journals A thermodynamic formulation of root water uptake

2016 ◽  
Vol 20 (8) ◽  
pp. 3441-3454 ◽  
Author(s):  
Anke Hildebrandt ◽  
Axel Kleidon ◽  
Marcel Bechmann
Keyword(s):  
Soil Water ◽  
Water Uptake ◽  
Water Distribution ◽  
Bound Water ◽  
Root Water Uptake ◽  
Flow Path ◽  
Thermodynamic Evaluation ◽  
Entire Flow ◽  
Soil Water Distribution

Abstract. By extracting bound water from the soil and lifting it to the canopy, root systems of vegetation perform work. Here we describe how root water uptake can be evaluated thermodynamically and demonstrate that this evaluation provides additional insights into the factors that impede root water uptake. We derive an expression that relates the energy export at the base of the root system to a sum of terms that reflect all fluxes and storage changes along the flow path in thermodynamic terms. We illustrate this thermodynamic formulation using an idealized setup of scenarios with a simple model. In these scenarios, we demonstrate why heterogeneity in soil water distribution and rooting properties affect the impediment of water flow even though the mean soil water content and rooting properties are the same across the scenarios. The effects of heterogeneity can clearly be identified in the thermodynamics of the system in terms of differences in dissipative losses and hydraulic energy, resulting in an earlier start of water limitation in the drying cycle. We conclude that this thermodynamic evaluation of root water uptake conveniently provides insights into the impediments of different processes along the entire flow path, which goes beyond resistances and also accounts for the role of heterogeneity in soil water distribution.

Leaf Gas Exchange and Water Relations of Lupins and Wheat. II. Root and Shoot Water Relations of Lupin During Drought-Induced Stomatal Closure

1989 ◽  
Vol 16 (5) ◽  
pp. 415 ◽  
Author(s):  
CR Jensen ◽  
IE Henson ◽  
NC Turner
Keyword(s):  
Water Potential ◽  
Soil Water ◽  
Water Transport ◽  
Water Uptake ◽  
Water Relations ◽  
Leaf Gas Exchange ◽  
Stomatal Closure ◽  
Soil Water Potential ◽  
Root Water Uptake ◽  
Leaf Conductance

Plants of Lupinus cosentinii Guss. cv. Eregulla were grown in a sandy soil in large containers in a glasshouse and exposed to drought by withholding water. Under these conditions stomatal closure had previously been shown to be initiated before a significant reduction in leaf water potential was detected. In the experiments reported here, no significant changes were found in water potential or turgor pressure of roots or leaves when a small reduction in soil water potential was induced which led to a 60% reduction in leaf conductance. The decrease in leaf conductance and root water uptake closely paralleled the fraction of roots in wet soil. By applying observed data of soil water and root characteristics, and root water uptake for whole pots in a single-root model, the average water potential at the root surface was calculated. Potential differences for water transport in the soil-plant system, and the resistances to water flow were estimated using the 'Ohm's Law' analogy for water transport. Soil resistance was negligible or minor, whereas the root resistance accounted for 61-72% and the shoot resistance accounted for about 30% of the total resistance. The validity of the measurements and calculations is discussed and the possible role of root- to-shoot communication raised.

Water drawdown by radish (Raphanus sativus L.) multiple-root systems evaluated using computed tomography

Soil Research ◽  
2008 ◽  
Vol 46 (3) ◽  
pp. 228
Author(s):  
M. A. Hamza ◽  
S. H. Anderson ◽  
L. A. G. Aylmore
Keyword(s):  
Computed Tomography ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Water Uptake ◽  
Root Zone ◽  
Multiple Root ◽  
Root Systems ◽  
Bulk Soil ◽  
Water Drawdown

Although measurements of water drawdown by single radish root systems have been previously published by the authors, further research is needed to evaluate water drawdown patterns in multiple-root systems. The objective of this study was to compare water transpiration patterns estimated using X-ray computed tomography (CT) with the traditional gravimetric method and to evaluate the effects of variably spaced multiple root systems on soil water content and corresponding water content gradients. Water drawdown showed a dual pattern in which it increased rapidly when soil water content was high at the beginning of transpiration, then slowed down to an almost constant level with time as water content decreased. These results contrast with the single-root system wherein transpiration rates initially increased rapidly and then slowly increased with time. Water uptake estimated using the CT method was observed to be 27–38% lower than the gravimetrically estimated water uptake; this difference was attributed to lower water uptake for the upper 30 mm layer (CT measured) than lower layers due to differences in root density. However, good correlation (r = 0.97) was found between both measurement methods. The drawdown patterns for multiple root systems showed a convex shape from the root surface to the bulk soil, compared with a nearly linear shape for single roots. The water content drawdown areas and the drawdown distances for multiple root systems were found to be much larger than those corresponding to single radish roots. Differential water content gradients were observed for roots spaced at 15-mm distances compared with 3–4-mm distances. These differential gradients from the bulk soil towards the root-zone occurred probably creating localised water potential gradients within the root-zone, which moved water from between roots to root surfaces. The lowest water content values were located in the inter-root areas. The CT-scanned layer probably acted as one drawdown area with particularly higher water drawdown from the inter-root areas.

scholarly journals Diurnal variation in xylem water isotopic signature biases depth of root-water uptake estimates

2019 ◽  
Author(s):  
Hannes De Deurwaerder ◽  
Marco D. Visser ◽  
Matteo Detto ◽  
Pascal Boeckx ◽  
Félicien Meunier ◽  
...  
Keyword(s):  
Diurnal Variation ◽  
Soil Water ◽  
Water Uptake ◽  
Sap Flow ◽  
Soil Water Potential ◽  
Root Water Uptake ◽  
Isotopic Signature ◽  
Stem Length ◽  
Individual Plant ◽  
List Type

SummaryStable water isotopes are a powerful and widely used tool to derive the depth of root water uptake (RWU) in lignified plants. Uniform xylem water isotopic signature (i-H2O-xyl) along the length of a lignified plant is a central assumption, which has never been properly evaluated.Here we studied the effects of diurnal variation in RWU, sap flow velocity and various other soil and plant parameters on i-H2O-xyl signature within a plant using a mechanistic plant hydraulic model.Our model predicts significant variation in i-H2O-xyl along the full length of an individual plant arising from diurnal RWU fluctuations and vertical soil water heterogeneity. Moreover, significant differences in i-H2O-xyl emerge between individuals with different sap flow velocities. We corroborated our model predictions with field observations from French Guiana and northwestern China. Modelled i-H2O-xyl varied considerably along stem length ranging up to 18.3‰ in δ2H and 2.2‰ in δ18O, largely exceeding the range of measurement error.Our results show clear violation of the fundamental assumption of uniform i-H2O-xyl and occurrence of significant biases when using stable isotopes to assess RWU. As a solution, we propose to include monitoring of sap flow and soil water potential for more robust RWU depth estimates.

Impact of soil water potential pattern on root water uptake distribution and leaf water potential

2021 ◽  
Author(s):  
Ali Mehmandoost Kotlar ◽  
Mathieu Javaux
Keyword(s):  
Water Potential ◽  
Root System ◽  
Soil Water ◽  
Water Flow ◽  
Water Uptake ◽  
Leaf Water Potential ◽  
Root Water Uptake ◽  
Leaf Water ◽  
Hydraulic Lift ◽  
Water Potentials

<p>Root water uptake is a major process controlling water balance and accounts for about 60% of global terrestrial evapotranspiration. The root system employs different strategies to better exploit available soil water, however, the regulation of water uptake under the spatiotemporal heterogeneous and uneven distribution of soil water is still a major question. To tackle this question, we need to understand how plants cope with this heterogeneity by adjustment of above ground responses to partial rhizosphere drying. Therefore, we use R-SWMS simulating soil water flow, flow towards the roots, and radial and the axial flow inside the root system to perform numerical experiments on a 9-cell gridded rhizotrone (50 cm×50 cm). The water potentials in each cell can be varied and fixed for the period of simulation and no water flow is allowed between cells while roots can pass over the boundaries. Then a static mature maize root architecture to different extents invaded in all cells is subjected to the various arrangements of cells' soil water potentials. R-SWMS allows determining possible hydraulic lift in drier areas. With these simulations, the variation of root water and leaf water potential will be determined and the role of root length density in each cell and corresponding average soil-root water potential will be statistically discussed.</p>

Root Water Uptake as Simulated by Three Soil Water Flow Models

2012 ◽  
Vol 11 (3) ◽  
pp. vzj2012.0018 ◽  
Author(s):  
Peter de Willigen ◽  
Jos C. van Dam ◽  
Mathieu Javaux ◽  
Marius Heinen
Keyword(s):  
Soil Water ◽  
Water Flow ◽  
Water Uptake ◽  
Root Water Uptake ◽  
Flow Models ◽  
Soil Water Flow

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.

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