scholarly journals Using Soil Moisture Data to Estimate Evapotranspiration and Development of a Physically Based Root Water Uptake Model

10.5772/18040 ◽  
2012 ◽  
Author(s):  
Nirjhar Shah ◽  
Mark Ross ◽  
Ken Trout
Keyword(s):  
Soil Moisture ◽  
Water Uptake ◽  
Root Water Uptake ◽  
Soil Moisture Data ◽  
Physically Based

Reconstructing Root Water Uptake from isotopic data and physically-based models: looking at recent effort and proposing a path forward

2020 ◽  
Author(s):  
Youri Rothfuss ◽  
Valentin Couvreur ◽  
Félicien Meunier ◽  
Hannes De Deurwaerder ◽  
Marco D. Visser ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Isotopic Composition ◽  
Water Uptake ◽  
Plant Root ◽  
Water Status ◽  
Bayesian Models ◽  
Root Water Uptake ◽  
Recent Effort ◽  
Isotope Data ◽  
Physically Based

<p>In the past decade, plant root water uptake (RWU) has been a major focus of ecohydrological studies employing water stable isotopes. The interest of the isotopic community for RWU rose concomitantly to the development of open-access multi-source mixing models based on Bayesian inference. Another more general reason was certainly the decrease in analytical cost with the advent of isotope-specific laser absorption spectrometry. The isotopic methodology used to determine relative profiles of RWU works on the premises that (i) RWU does not fractionate stable isotopes in water and (ii) the isotopic composition of water inside the xylem vessel of the last non-evaporating part of the plant (typically the stem) is that of RWU. Following a simple mass balance approach, the isotopic composition of RWU can be linked back by inversion to contributions to RWU (i.e., relative RWU) of a set of potential water sources (of known isotopic compositions) originating from the soil profile.</p><p>In recent research, the preferred tool for inverting water isotope data was Bayesian models and the literature shows that only a handful of studies complemented isotope analysis with observation of plant water status and flow. Consequently, most of the gathered information on RWU cannot be used to test hypotheses on which are built physically-based soil-root water flow models. The authors have on the other hand initiated an effort within the framework of dual experimental-modeling approaches, where tightly-controlled experiments are thought and prepared in order to validate, parameterize models, or test hypotheses. The present contribution gives an overview of the different attempts at integrating both water and isotope observations types and confronting them to model simulations explicitly accounting for root system architecture and hydraulic properties. It addresses the meaningfulness and limitations of isotope data, especially in the context of labeling experiments when treated with statistical (e.g. Bayesian) models. We finally propose a way forward and present improvements to be achieved on both experimental and modeling sides to increase the reliability and precision of isotope-derived estimates of RWU.</p>

scholarly journals A thermodynamic formulation of root water uptake

2015 ◽  
Vol 12 (12) ◽  
pp. 13383-13413
Author(s):  
A. Hildebrandt ◽  
A. Kleidon ◽  
M. Bechmann
Keyword(s):  
Root System ◽  
Water Uptake ◽  
Water Distribution ◽  
Bound Water ◽  
Root Water Uptake ◽  
Flow Path ◽  
Thermodynamic Evaluation ◽  
Flux Boundary Condition ◽  
Physically Based ◽  
Energy Domain

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.

scholarly journals Estimates of tree root water uptake from soil moisture profile dynamics

2019 ◽  
Author(s):  
Conrad Jackisch ◽  
Samuel Knoblauch ◽  
Theresa Blume ◽  
Erwin Zehe ◽  
Sibylle K. Hassler
Keyword(s):  
Time Series ◽  
Soil Moisture ◽  
Water Uptake ◽  
Sap Flow ◽  
Water Cycle ◽  
Xylem Sap ◽  
Root Water Uptake ◽  
Soil Conditions ◽  
Diurnal Changes ◽  
Moisture Profile

Abstract. Root water uptake (RWU) as one important process in the terrestrial water cycle can help to better understand the interactions in the soil water plant system. We conducted a field study monitoring soil moisture profiles in the rhizosphere of beech trees at two sites with different soil conditions. We infer RWU from step-shaped, diurnal changes in soil moisture. While this approach is a feasible, easily implemented method during wet and moderate conditions, limitations were identified during drier states and for more heterogeneous soil settings. A comparison with time series of xylem sap velocity reveals that RWU and sap flow are complementary measures of the transpiration process. The high correlation between the sap flow time series of the two sites, but lower correlation between the RWU time series, suggests that the trees adapt RWU to soil heterogeneity and site differences.

scholarly journals Using StorAge Selection functions to quantify ecohydrological controls on the time-variant age of evapotranspiration, soil water, and recharge

2018 ◽  
Author(s):  
Aaron A. Smith ◽  
Doerthe Tetzlaff ◽  
Chris Soulsby
Keyword(s):  
Soil Moisture ◽  
Surface Water ◽  
Soil Water ◽  
Water Uptake ◽  
Root Water Uptake ◽  
Soil Evaporation ◽  
Root Uptake ◽  
Water Fluxes ◽  
Near Surface ◽  
Moisture Conditions

Abstract. Quantifying ecohydrological controls on soil water availability is essential to understand temporal variations in catchment storage. Soil water is subject to numerous time-variable fluxes (evaporation, root-uptake, and recharge), each with different water ages which in turn affect the age of water in storage. Here, we adapt StorAge Selection (SAS) function theory to investigate water flow in soils and identify soil evaporation and root-water uptake sources from depth. We use this to quantify the effects of soil-vegetation interactions on the inter-relationships between water fluxes, storage, and age. The novel modification of the SAS function framework is tested against empirical data from two contrasting soil-vegetation units in the Scottish Highlands; these are characterised by significant preferential flow, transporting younger water through the soil during high soil moisture conditions. Dominant young water fluxes, along with relatively low rainfall intensities, explain relatively stable soil water ages through time and with depth. Soil evaporation sources were more time-invariant with high preference for near-surface water, independent of soil moisture conditions, and resulting in soil evaporation water ages similar to near-surface soil waters (mean age: 50–65 days). Sources of root-water uptake were more variable: preferential near-surface water uptake occurred in wet conditions, with a deeper root-uptake source during dry soil conditions, which resulted in more variable water ages of transpiration (mean age: 56–79 days). The simple model structure provides a parsimonious means of constraining the water age of multiple fluxes from the upper part of the critical zone during time-varying conditions improving our understanding of vegetation influences on catchment scale water fluxes.

scholarly journals Isotopic approaches to quantifying root water uptake and redistribution: a review and comparison of methods

2016 ◽  
Author(s):  
Youri Rothfuss ◽  
Mathieu Javaux
Keyword(s):  
Isotopic Composition ◽  
Statistical Methods ◽  
Water Uptake ◽  
Isotopic Analysis ◽  
Root Water Uptake ◽  
Water Sources ◽  
Mixing Model ◽  
Stable Isotopic Analysis ◽  
Stable Isotopic ◽  
Physically Based

Abstract. Plant root water uptake (RWU) and release (i.e., hydraulic redistribution – HR, and its particular case hydraulic lift – HL) have been documented for the past five decades from water stable isotopic analysis. By comparing the (hydrogen or oxygen) stable isotopic composition of plant xylem water to those of potential contributive water sources (e.g., water from different soil layers, groundwater, water from recent precipitation or from a nearby stream) authors could determine the relative contributions of these water sources to RWU. Other authors have confirmed the existence of HR and HL from the isotopic analysis of the plant xylem water following a labelling pulse. In this paper, the different methods used for locating / quantifying relative contributions of water sources to RWU (i.e., graphical inference, statistical (e.g., Bayesian) multi-source linear mixing models) are reviewed with emphasis on their respective advantages and drawbacks. The graphical and statistical methods are tested against a physically based analytical RWU model during a series of virtual experiments differing in the depth of the groundwater table, the soil surface water status, and the plant transpiration rate value. The benchmarking of these methods illustrates the limitations of the graphical and statistical methods (e.g., their inability to locate or quantify HR) while it underlines the performance of one Bayesian mixing model, but only when the number of considered water sources in the soil is the highest to closely reflect the vertical distribution of the soil water isotopic composition. The simplest two end-member mixing model is also successfully tested when all possible sources in the soil can be identified to define the two end-members and compute their isotopic compositions. Finally, future challenges in studying RWU with stable isotopic analysis are evocated with focus on new isotopic monitoring methods and sampling strategies, and on the implementation of isotope transport in physically based RWU models.

scholarly journals Big root approximation of site-scale vegtation water uptake

2019 ◽  
Author(s):  
Martin Bouda
Keyword(s):  
Soil Moisture ◽  
Water Uptake ◽  
Land Surface ◽  
Land Surface Model ◽  
Root Water Uptake ◽  
Surface Model ◽  
Summer Drought ◽  
Ohm’S Law ◽  
Ohm's Law ◽  
Vegetation Water

AbstractLand surface model (LSM) predictions of soil moisture and transpiration under water-limited conditions suffer from biases due to a lack of mechanistic process description of vegetation water uptake. Here, I derive a ‘big root’ approach from the porous pipe equation for root water uptake and compare its predictions of soil moistures during the 2010 summer drought at the Wind River Crane site to two previously used Ohm’s law analogue plant hydraulic models. Structural error due to inadequate representation of root system architecture (RSA) in both Ohm’s law analogue models yields significant and predictable moisture biases. The big root model greatly reduces these as it better represents RSA effects on pressure gradients and flows within the roots. It represents a major theoretical advance in understanding vegetation water limitation at site scale with potential to improve LSM predictions of soil moisture, temperature and surface heat, water, and carbon fluxes.

Quantifying how plants with different species-specific water-use strategies cope with the same drought-prone hydro-ecological conditions

2020 ◽  
Author(s):  
Deepanshu Khare ◽  
Gernot Bodner ◽  
Mathieu Javaux ◽  
Jan Vanderborght ◽  
Daniel Leitner ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Drought Stress ◽  
Water Potential ◽  
Water Uptake ◽  
Hydraulic Properties ◽  
Root Water Uptake ◽  
Leaf Water ◽  
Plant Water ◽  
Soil Hydraulic Properties ◽  
Stomatal Control

<p>Plant transpiration and root water uptake are dependent on multiple traits that interact with site soil characteristics and environmental factors such as radiation, atmospheric temperature, relative humidity, and soil-moisture content. Models of root architecture and functions are increasingly employed to simulate root-soil interactions. Root water uptake is thereby affected by the root hydraulic architecture, soil moisture conditions, soil hydraulic properties, and the transpiration demand as controlled by atmospheric conditions. Stomatal conductance plays a vital role in regulating transpiration in plants. We performed simulations of plant water uptake for plants having different mechanisms to control transpiration, spanned by isohydric/anisohydric spectrum. Isohydric plants follow the strategy to close their stomata in order to maintain the leaf water potential at a constant level, while anisohydric plants leave their stomata open when leaf water potentials fall due to drought stress. Modelling the stomatal regulation effectively will result in a more reliable model that will regulate the excessive loss of water. We implemented hydraulic and chemical stomatal control<br>of root water uptake following the current approach where stomatal control is regulated by simulated water potential and/or chemical signal concentration. In order to maintain water uptake from dry soil, low plant water potentials are required, which may lead to reversible or permanent cavitation. We parameterise our model with field data, including climate data and soil hydraulic properties under different tillage conditions. This helps us to understand the behaviour of different crops under drought conditions and predict at which growing stage the stress hits the plant. We conducted the simulations for different scenarios to study the effect of hydraulic and chemical regulation on root system performance under drought stress.</p>

scholarly journals An optimality-based model of the coupled soil moisture and root dynamics

2008 ◽  
Vol 12 (3) ◽  
pp. 913-932 ◽  
Author(s):  
S. J. Schymanski ◽  
M. Sivapalan ◽  
M. L. Roderick ◽  
J. Beringer ◽  
L. B. Hutley
Keyword(s):  
Soil Moisture ◽  
Water Uptake ◽  
Root Distribution ◽  
Root Respiration ◽  
Root Water Uptake ◽  
Dry Season ◽  
Soil Moisture Dynamics ◽  
Model Based ◽  
Vertical Root Distribution ◽  
Moisture Dynamics

Abstract. The main processes determining soil moisture dynamics are infiltration, percolation, evaporation and root water uptake. Modelling soil moisture dynamics therefore requires an interdisciplinary approach that links hydrological, atmospheric and biological processes. Previous approaches treat either root water uptake rates or root distributions and transpiration rates as given, and calculate the soil moisture dynamics based on the theory of flow in unsaturated media. The present study introduces a different approach to linking soil water and vegetation dynamics, based on vegetation optimality. Assuming that plants have evolved mechanisms that minimise costs related to the maintenance of the root system while meeting their demand for water, we develop a model that dynamically adjusts the vertical root distribution in the soil profile to meet this objective. The model was used to compute the soil moisture dynamics, root water uptake and fine root respiration in a tropical savanna over 12 months, and the results were compared with observations at the site and with a model based on a fixed root distribution. The optimality-based model reproduced the main features of the observations such as a shift of roots from the shallow soil in the wet season to the deeper soil in the dry season and substantial root water uptake during the dry season. At the same time, simulated fine root respiration rates never exceeded the upper envelope determined by the observed soil respiration. The model based on a fixed root distribution, in contrast, failed to explain the magnitude of water use during parts of the dry season and largely over-estimated root respiration rates. The observed surface soil moisture dynamics were also better reproduced by the optimality-based model than the model based on a prescribed root distribution. The optimality-based approach has the potential to reduce the number of unknowns in a model (e.g. the vertical root distribution), which makes it a valuable alternative to more empirically-based approaches, especially for simulating possible responses to environmental change.

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