A thermodynamic formulation of root water uptake

Abstract. By extracting bound water from the soil and lifting it to the canopy, root systems of vegetation perform work. Here we describe how the energetics involved in root water uptake can be quantified. The illustration is done using a simple, four-box model of the soil-root system to represent heterogeneity and a parameterization in which root water uptake is driven by the xylem potential of the plant with a fixed flux boundary condition. We use this approach to evaluate the effects of soil moisture heterogeneity and root system properties on the dissipative losses and export of energy involved in root water uptake. For this, we derive an expression that relates the energy export at the root collar to a sum of terms that reflect all fluxes and storage changes along the flow path in thermodynamic terms. We conclude that such a thermodynamic evaluation of root water uptake conveniently provides insights into the impediments of different processes along the entire flow path and explicitly accounting not only for the resistances along the flow path and those imposed by soil drying but especially the role of heterogenous soil water distribution. The results show that least energy needs to be exported and dissipative losses are minimized by a root system if it extracts water uniformly from the soil. This has implications for plant water relations in forests where canopies generate heterogenous input patterns. Our diagnostic in the energy domain should be useful in future model applications for quantifying how plants can evolve towards greater efficiency in their structure and function, particularly in heterogenous soil environments. Generally, this approach may help to better describe heterogeneous processes in the soil in a simple, yet physically-based way.

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Root Water Uptake and Soil Water Distribution: Test of an Availability Concept

Soil Science Society of America Journal ◽

10.2136/sssaj1984.03615995004800020002x ◽

1984 ◽

Vol 48 (2) ◽

pp. 233-237 ◽

Cited By ~ 23

Author(s):

R.J. Lascano ◽

C.H.M. van Bavel

Keyword(s):

Soil Water ◽

Water Uptake ◽

Water Distribution ◽

Root Water Uptake ◽

Soil Water Distribution

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Root System of Olive Trees ( Olea Europaed L.) Based on Runoff Harvesting System During Dry Period

10.20944/preprints201911.0016.v1 ◽

2019 ◽

Author(s):

Hung-Phi Nguyen ◽

Thao Nguyen Bich

Keyword(s):

Soil Water ◽

Water Uptake ◽

Water Distribution ◽

Root Water Uptake ◽

Severe Drought ◽

Atmospheric Conditions ◽

Run Off ◽

Relative Water ◽

Olive Trees ◽

Controlled Flooding

This paper presents a study of a field trial experiment at olive orchard irrigated by runoff harvesting system under a dry climate which was carried out on 5-year-old olive trees (Olea europaea. L, cv. Barnea) in the middle of Negev desert, starting right after the floods, onwards during the summer growing season. The beginning of the experiment occurred after 2 years with little rain and no run-off events. The olive trees were under severe drought stress when we first initiated controlled flooding in 2017. In the second research year (2018), a massive natural flood had occurred at the end of April. Results show that the water distribution within the soil was highly inhomogeneous even under flood conditions. Soil water loss rate, due to transpiration was mainly correlated with the total amount of soil water and not atmospheric conditions. The relative root water uptake from shallow soil layers (0.3-1.5m) gradually reduced along the season, while the relative water uptake from the deeper layers (1.5-4m) became more pronounced.

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

Hydrology and Earth System Sciences ◽

10.5194/hess-14-279-2010 ◽

2010 ◽

Vol 14 (2) ◽

pp. 279-289 ◽

Cited By ~ 45

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.

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

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-6-4233-2009 ◽

2009 ◽

Vol 6 (3) ◽

pp. 4233-4264 ◽

Cited By ~ 7

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.

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Paleotopography and soil-water distribution on concave slopes of hilly Paraiba do Sul basin (south-eastern Brazil)/Paléotopographie et distribution de l'eau dans les sols sur des versants concaves du Sud-Est brésilien

Géomorphologie relief processus environnement ◽

10.3406/morfo.1996.883 ◽

1996 ◽

Vol 2 (3) ◽

pp. 29-40

Author(s):

Marcelo Accioly Teixeira de Oliveira

Keyword(s):

Soil Water ◽

Water Distribution ◽

South Eastern ◽

Eastern Brazil ◽

Soil Water Distribution

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Analysis of Soil Water Response to Grass Transpiration

Soil and Water Research ◽

10.17221/6510-swr ◽

2013 ◽

Vol 1 (No. 3) ◽

pp. 85-98

Author(s):

Dohnal Michal ◽

Dušek Jaromír ◽

Vogel Tomáš ◽

Herza Jiří

Keyword(s):

Soil Water ◽

Water Uptake ◽

Preferential Flow ◽

Water Movement ◽

Control Volume ◽

Water Pressure ◽

Lower Boundary ◽

Root Water Uptake ◽

Water Dynamics ◽

Soil Water Dynamics

This paper focuses on numerical modelling of soil water movement in response to the root water uptake that is driven by transpiration. The flow of water in a lysimeter, installed at a grass covered hillslope site in a small headwater catchment, is analysed by means of numerical simulation. The lysimeter system provides a well defined control volume with boundary fluxes measured and soil water pressure continuously monitored. The evapotranspiration intensity is estimated by the Penman-Monteith method and compared with the measured lysimeter soil water loss and the simulated root water uptake. Variably saturated flow of water in the lysimeter is simulated using one-dimensional dual-permeability model based on the numerical solution of the Richards’ equation. The availability of water for the root water uptake is determined by the evaluation of the plant water stress function, integrated in the soil water flow model. Different lower boundary conditions are tested to compare the soil water dynamics inside and outside the lysimeter. Special attention is paid to the possible influence of the preferential flow effects on the lysimeter soil water balance. The adopted modelling approach provides a useful and flexible framework for numerical analysis of soil water dynamics in response to the plant transpiration.

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

Water ◽

10.3390/w11030425 ◽

2019 ◽

Vol 11 (3) ◽

pp. 425 ◽

Cited By ~ 3

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.

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