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  • 1
    Language: English
    In: Plant physiology, April 2014, Vol.164(4), pp.1619-27
    Description: Over the last decade, investigations on root water uptake have evolved toward a deeper integration of the soil and roots compartment properties, with the goal of improving our understanding of water acquisition from drying soils. This evolution parallels the increasing attention of agronomists to suboptimal crop production environments. Recent results have led to the description of root system architectures that might contribute to deep-water extraction or to water-saving strategies. In addition, the manipulation of root hydraulic properties would provide further opportunities to improve water uptake. However, modeling studies highlight the role of soil hydraulics in the control of water uptake in drying soil and call for integrative soil-plant system approaches.
    Keywords: Desiccation ; Soil ; Plants -- Metabolism ; Water -- Metabolism
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 2
    In: Nature, 2016, Vol.536(7617), p.E1
    Description: In their study, Evaristo et al.1 collected an extensive data set on the basis of which they statistically determined the isotopic compositions of the plant water source (δ 18Ointersect and δ 2Hintersect, called respectively δ 18Ointercept and δ 2Hintercept in their paper) as the x and y coordinates in (δ 18O, δ 2H) space of the intersection between the local meteoric water line (LMWL) and the plant xylem water 'evaporation line' (EL) for a range of climates and vegetation types.
    Keywords: Isotopes ; Groundwater ; Groundwater Recharge ; Stream Flow ; Precipitation ; Botany ; Flowers & Plants;
    ISSN: 0028-0836
    E-ISSN: 1476-4687
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  • 3
    Language: English
    In: Journal of Hydrology, 2015, Vol.528, p.192(14)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jhydrol.2015.06.031 Byline: Andres Penuela, Mathieu Javaux, Charles L. Bielders Abstract: * Surface roughness and slope have remarkable effects on overland flow connectivity. * A conceptualization of surface roughness by rectangular depressions is proposed. * Equations to predict runoff-relevant features of connectivity are proposed. * A novel equation is proposed to predict the maximum depression storage (DS.sub.max). * DS.sub.max equation performed better than empirical expressions found in the literature. Article History: Received 11 March 2015; Revised 13 May 2015; Accepted 13 June 2015 Article Note: (miscellaneous) This manuscript was handled by Konstantine P. Georgakakos, Editor-in-Chief, with the assistance of Venkat Lakshmi, Associate Editor
    ISSN: 0022-1694
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Journal of Hydrology, 2011, Vol.403(3), pp.213-223
    Description: ► Distributed runoff models may be improved using grid-scale connectivity properties. ► The relative surface connection (RSC) function captures subgrid connectivity. ► A weighted-surface procedure is proposed to account for surface detention. ► The RSC function may be represented by conceptual multiple-compartment topographies. ► A ‘uniform’ multiple-compartment representation performed best. The spatial configuration of micro-topography affects the runoff connectivity at the interrill scale and, therefore, the shape of the hydrograph. In a previous study, we demonstrated the ability of the so-called Relative Surface Connection (RSC) function to capture, at the grid scale, the evolution of the contributing area as a function of the depression storage filling. However, this function neglects the effect of surface detention, which is proportional to the runoff rate and which must be taken into account if one wants to predict correctly the discharge dynamics. Therefore we tested two corrective procedures in association with the RSC function to integrate, at the grid scale, the effects of both depression storage and surface detention dynamics. The weighted-source corrective procedure consists in weighing the effective supply of water between depression storage and runoff using the RSC function. The weighted-surface corrective procedure consists in splitting a single grid into parallel independent strips whose sizes depend on the RSC function and which activate at various times and then participate to the global runoff production. Those methods allowed to mimic in a simple way and at the grid scale synthetical and experimental hydrographs for complex subgrid micro-topographies. The weighted-source and especially the weighted-surface corrective procedures improved the hydrograph prediction compared to the classical approach where runoff only starts when depression storage capacity is full. In a purely numerical framework with four runoff scenarios on highly contrasted micro-topographies, this improvement was reflected in a significant increase of the median Nash and Sutcliffe coefficients ( = 0.29 for the classical approach, = 0.67 for the weighted-source procedure and = 0.94 for the weighted-surface procedure). For the depression storage filling, an alternative to the Linsley equation was found and allowed a better description of surface runoff before maximal depression storage was reached. This was reflected in an increase of the computed for 27 overland flow experiments under laboratory conditions and their equivalent model results ( = 0.89 for the Linsley approach, = 0.94 with the proposed ‘uniform’ multiple-compartment conceptual approach, and = 0.85 for the classical approach where runoff only starts when depression storage capacity is full).
    Keywords: Connectivity ; Grid-Scale Modeling ; Runoff ; Upscaling ; Depression Storage ; Surface Detention ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 5
    Language: English
    In: Plant and Soil, 2011, Vol.341(1), pp.233-256
    Description: The estimation of root water uptake and water flow in plants is crucial to quantify transpiration and hence the water exchange between land surface and atmosphere. In particular the soil water extraction by plant roots which provides the water supply of plants is a highly dynamic and non-linear process interacting with soil transport processes that are mainly determined by the natural soil variability at different scales. To better consider this root-soil interaction we extended and further developed a finite element tree hydro-dynamics model based on the one-dimensional (1D) porous media equation. This is achieved by including in addition to the explicit three-dimensional (3D) architectural representation of the tree crown a corresponding 3D characterisation of the root system. This 1D xylem water flow model was then coupled to a soil water flow model derived also from the 1D porous media equation. We apply the new model to conduct sensitivity analysis of root water uptake and transpiration dynamics and compare the results to simulation results obtained by using a 3D model of soil water flow and root water uptake. Based on data from lysimeter experiments with young European beech trees ( Fagus silvatica L.) is shown, that the model is able to correctly describe transpiration and soil water flow. In conclusion, compared to a fully 3D model the 1D porous media approach provides a computationally efficient alternative, able to reproduce the main mechanisms of plant hydro-dynamics including root water uptake from soil.
    Keywords: Transpiration ; Plant hydro-dynamics model ; Root water uptake ; European beech ; Porous media equation
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 6
    Language: English
    In: Plant and Soil, 2014, Vol.384(1), pp.93-112
    Description: Aims A simulation model to demonstrate that soil water potential can regulate transpiration, by influencing leaf water potential and/or inducing root production of chemical signals that are transported to the leaves. Methods Signalling impacts on the relationship between soil water potential and transpiration were simulated by coupling a 3D model for water flow in soil, into and through roots (Javaux et al. 2008) with a model for xylem transport of chemicals (produced as a function of local root water potential). Stomatal conductance was regulated by simulated leaf water potential (H) and/or foliar chemical signal concentrations (C; H+C). Split-root experiments were simulated by varying transpiration demands and irrigation placement. Results While regulation of stomatal conductance by chemical transport was unstable and oscillatory, simulated transpiration over time and root water uptake from the two soil compartments were similar for both H and H+C regulation. Increased stomatal sensitivity more strongly decreased transpiration, and decreased threshold root water potential (below which a chemical signal is produced) delayed transpiration reduction. Conclusions Although simulations with H+C regulation qualitatively reproduced transpiration of plants exposed to partial rootzone drying (PRD), long-term effects seemed negligible. Moreover, most transpiration responses to PRD could be explained by hydraulic signalling alone. Keywords Soil-root modeling * R-SWMS * Hormonal Signaling * Stomatal conductance * Partial rootzone drying
    Keywords: Soil-root modelling ; R-SWMS ; Hormonal signalling ; Stomatal conductance ; Partial rootzone drying
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 7
    Language: English
    In: Journal of Hydrology, September 2015, Vol.528, pp.192-205
    Description: Surface micro-topography and slope drive the hydrological response of plots through the gradual filling of depressions as well as the establishment of hydraulic connections between overflowing depressions. Therefore, quantifying and understanding the effects of surface roughness and slope on plot-scale overland flow connectivity is crucial to improve current hydrological modeling and runoff prediction. This study aimed at establishing predictive equations relating structural and functional connectivity indicators in function of slope and roughness. The Relative Surface Connection function (RSCf) was used as a functional connectivity indicator was applied. Three characteristic parameters were defined to characterize the RSCf: the surface initially connected to the outlet, the connectivity threshold and the maximum depression storage (DS ). Gaussian surface elevation fields (6 m × 6 m) were generated for a range of slopes and roughnesses (sill and range of the variogram). A full factorial of 6 slopes (0–15%), 6 values of (50–400 mm) and 6 values of (2–40 mm) was considered, and the RSCf calculated for 10 realizations of each combination. Results showed that the characteristic parameters of the RSCf are greatly influenced by , and slope. At low slopes and high ratios of /2 , the characteristic parameters of the RSCf appear linked to a single component of the surface roughness ( or ). On the contrary, both and are needed to predict the RSCf at high slopes and low ratios of /2 . A simple conceptualization of surface depressions as rectangles, whose shape was determined by and , allowed deriving simple mathematical expressions to estimate the characteristic parameters of the RSCf in function of , and slope. In the case of DS , the proposed equation performed better than previous empirical expressions found in the literature which do not account for the horizontal component of the surface roughness. The proposed expressions allow estimating the characteristic points of the RSCf with reasonable accuracy and could therefore prove useful for integrating plot-scale overland flow connectivity into hydrological models whenever the RSCf presents a well-defined connectivity threshold.
    Keywords: Overland Flow ; Hydrological Connectivity ; Roughness ; Slope ; Plot-Scale ; Depression Storage ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 8
    Language: English
    In: Plant and Soil, 2013, Vol.372(1), pp.93-124
    Description: Issue Title: In Memory of Horst Marschner Three-dimensional root architectural models emerged in the late 1980s, providing an opportunity to conceptualise and investigate that all important part of plants that is typically hidden and difficult to measure and study. These models have progressed from representing pre-defined root architectural arrangements, to simulating root growth in response to heterogeneous soil environments. This was done through incorporating soil properties and more complete descriptions of plant function, moving into the realm of functional-structural plant modelling. Modelling studies are often designed to investigate the relationship between root architectural traits and root distribution in soil, and the spatio-temporal variability of resource supply. Modelling root systems presents an opportunity to investigate functional tradeoffs between foraging strategies (i.e. shallow vs deep rooting) for contrasting resources (immobile versus mobile resources), and their dependence on soil type, rainfall and other environmental conditions. The complexity of the interactions between root traits and environment emphasises the need for models in which traits and environmental conditions can be independently manipulated, unlike in the real world. We provide an overview of the development of three-dimensional root architectural models from their origins, to their place today in the world of functional-structural plant modelling. The uses and capability of root architectural models to represent virtual plants and soil environment are addressed. We compare features of six current models, RootTyp, SimRoot, ROOTMAP, SPACSYS, R-SWMS, and RootBox, and discuss the future development of functional-structural root architectural modelling. Functional-structural root architectural models are being used to investigate numerous root-soil interactions, over a range of spatial scales. They are not only providing insights into the relationships between architecture, morphology and functional efficiency, but are also developing into tools that aid in the design of agricultural management schemes and in the selection of root traits for improving plant performance in specific environments.[PUBLICATION ]
    Keywords: Functional-structural modelling ; Heterogeneous soil environments ; Nutrient acquisition ; Root architecture ; Root growth ; Root modelling ; Simulation ; Three dimensions (3D) ; Water uptake
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 9
    Language: English
    In: Plant physiology, December 2018, Vol.178(4), pp.1689-1703
    Description: As water often limits crop production, a more complete understanding of plant water capture and transport is necessary. Here, we developed MECHA, a mathematical model that computes the flow of water across the root at the scale of walls, membranes, and plasmodesmata of individual cells, and used it to test hypotheses related to root water transport in maize (). The model uses detailed root anatomical descriptions and a minimal set of experimental cell properties, including the conductivity of plasma membranes, cell walls, and plasmodesmata, which yield quantitative and scale-consistent estimations of water pathways and root radial hydraulic conductivity ( ). MECHA revealed that the mainstream hydraulic theories derived independently at the cell and root segment scales are compatible only if osmotic potentials within the apoplastic domains are uniform. The results suggested that the convection-diffusion of apoplastic solutes explained most of the offset between estimated in pressure clamp and osmotic experiments, while the contribution of water-filled intercellular spaces was limited. Furthermore, sensitivity analyses quantified the relative impact of cortex and endodermis cell conductivity of plasma membranes on root and suggested that only the latter contributed substantially to due to the composite nature of water flow across roots. The explicit root hydraulic anatomy framework brings insights into contradictory interpretations of experiments from the literature and suggests experiments to efficiently address questions pertaining to root water relations. Its scale consistency opens avenues for cross-scale communication in the world of root hydraulics.
    Keywords: Hydrogeology – Analysis ; Hydrogeology – Electric Properties ; Hydrogeology – Models ; Hydraulic Flow – Analysis ; Hydraulic Flow – Electric Properties ; Hydraulic Flow – Models;
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 10
    Language: English
    In: Plant and soil, 2015, Vol.394(1), pp.109-126
    Description: AIMS: Stomata can close to avoid cavitation under decreased soil water availability. This closure can be triggered by hydraulic (‘H’) and/or chemical signals (‘C’, ‘H + C’). By combining plant hydraulic relations with a model for stomatal conductance, including chemical signalling, our aim was to derive direct relations that link soil water availability, expressed as fraction of roots in dry soil (fdᵣy), to transpiration reduction. METHODS: We used the mechanistic soil-root water flow model R-SWMS to verify this relation. Virtual split root experiments were simulated, comparing horizontal and vertical splits with varying fdᵣy and different strengths of stomatal regulation by chemical and hydraulic signals. RESULTS: Transpiration reduction predicted by the direct relations was in good agreement with numerical simulations. For small enough potential transpiration and large enough root hydraulic conductivity and stomatal sensitivity to chemical signalling isohydric plant behaviour originates from H + C control whereas anisohydric behaviour emerges from C control. For C control the relation between transpiration reduction and fdᵣy becomes independent of transpiration rate whereas H + C control results in stronger reduction for higher transpiration rates. CONCLUSION: Direct relations that link effective soil water potential and leaf water potential can describe different stomatal control resulting in contrasting behaviour. ; p. 109-126.
    Keywords: Plant Available Water ; Root Hydraulic Conductivity ; Stomata ; Leaf Water Potential ; Stomatal Conductance ; Roots ; Water Flow ; Mathematical Models ; Stomatal Movement ; Leaves ; Soil Water Potential
    ISSN: 0032-079X
    E-ISSN: 15735036
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