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Couvreur V.,Catholic University of Louvain | Couvreur V.,University of California at Davis | Vanderborght J.,Forschungszentrum Juelich GmbH | Draye X.,Catholic University of Louvain | Javaux M.,Catholic University of Louvain
Water Resources Research | Year: 2014

Soil water availability for plant transpiration is a key concept in agronomy. The objective of this study is to revisit this concept and discuss how it may be affected by processes locally influencing root hydraulic properties. A physical limitation to soil water availability in terms of maximal flow rate available to plant leaves (Qavail) is defined. It is expressed for isohydric plants, in terms of plant-centered variables and properties (the equivalent soil water potential sensed by the plant, ψseq; the root system equivalent conductance, Krs; and a threshold leaf water potential, ψleaf lim). The resulting limitation to plant transpiration is compared to commonly used empirical stress functions. Similarities suggest that the slope of empirical functions might correspond to the ratio of Krs to the plant potential transpiration rate. The sensitivity of Qavail to local changes of root hydraulic conductances in response to soil matric potential is investigated using model simulations. A decrease of radial conductances when the soil dries induces earlier water stress, but allows maintaining higher night plant water potentials and higher Qavail during the last week of a simulated 1 month drought. In opposition, an increase of radial conductances during soil drying provokes an increase of hydraulic redistribution and Qavail at short term. This study offers a first insight on the effect of dynamic local root hydraulic properties on soil water availability. By better understanding complex interactions between hydraulic processes involved in soil-plant hydrodynamics, better prospects on how root hydraulic traits mitigate plant water stress might be achieved. Key Points Soil water availability is expressed as a maximal possible water u © 2014. American Geophysical Union. All Rights Reserved.

Laloy E.,Belgian Nuclear Research Center | Huisman J.A.,Forschungszentrum Juelich GmbH | Jacques D.,Belgian Nuclear Research Center
Journal of Hydrology | Year: 2014

This study presents an novel Bayesian inversion scheme for high-dimensional undetermined TDR waveform inversion. The methodology quantifies uncertainty in the moisture content distribution, using a Gaussian Markov random field (GMRF) prior as regularization operator. A spatial resolution of 1cm along a 70-cm long TDR probe is considered for the inferred moisture content. Numerical testing shows that the proposed inversion approach works very well in case of a perfect model and Gaussian measurement errors. Real-world application results are generally satisfying. For a series of TDR measurements made during imbibition and evaporation from a laboratory soil column, the average root-mean-square error (RMSE) between maximum a posteriori (MAP) moisture distribution and reference TDR measurements is 0.04cm3cm-3. This RMSE value reduces to less than 0.02cm3cm-3 for a field application in a podzol soil. The observed model-data discrepancies are primarily due to model inadequacy, such as our simplified modeling of the bulk soil electrical conductivity profile. Among the important issues that should be addressed in future work are the explicit inference of the soil electrical conductivity profile along with the other sampled variables, the modeling of the temperature-dependence of the coaxial cable properties and the definition of an appropriate statistical model of the residual errors. © 2014 Elsevier B.V.

Draye X.,Catholic University of Louvain | Kim Y.,Catholic University of Louvain | Lobet G.,Catholic University of Louvain | Javaux M.,Catholic University of Louvain | Javaux M.,Forschungszentrum Juelich GmbH
Journal of Experimental Botany | Year: 2010

Due in part to recent progress in root genetics and genomics, increasing attention is being devoted to root system architecture (RSA) for the improvement of drought tolerance. The focus is generally set on deep roots, expected to improve access to soil water resources during water deficit episodes. Surprisingly, our quantitative understanding of the role of RSA in the uptake of soil water remains extremely limited, which is mainly due to the inherent complexity of the soil-plant continuum. Evidently, there is a need for plant biologists and hydrologists to develop together their understanding of water movement in the soil-plant system. Using recent quantitative models coupling the hydraulic behaviour of soil and roots in an explicit 3D framework, this paper illustrates that the contribution of RSA to root water uptake is hardly separable from the hydraulic properties of the roots and of the soil. It is also argued that the traditional view that either the plant or the soil should be dominating the patterns of water extraction is not generally appropriate for crops growing with a sub-optimal water supply. Hopefully, in silico experiments using this type of model will help explore how water fluxes driven by soil and plant processes affect soil water availability and uptake throughout a growth cycle and will embed the study of RSA within the domains of root hydraulic architecture and sub-surface hydrology. © 2010 The Author.

Muellenborn C.,Forschungszentrum Juelich GmbH | Cerboncini C.,Forschungszentrum Juelich GmbH
Plant Molecular Biology Reporter | Year: 2011

The necrotrophic pathogen Sclerotinia sclerotiorum is a causal agent of rot diseases in sunflower and is described as one of the most damaging pathogens of cultivated sunflower. Resistance to this pathogen is found in some genotypes of wild sunflower in particular characterised by significantly reduced lesion lengths in capitulum, stems and leaves. This study was conducted to characterise transcriptomic alterations during interaction of host and pathogen in lesion-surrounding areas of the leaf using differential display RT-PCR and to compare molecular responses between a resistant and a susceptible genotype. Leaves were examined during the first stages of pathogenesis (dpi 2, 3 and 4) after inoculation with S. sclerotiorum. By means of computational analysis of fluorescently labelled expression data, expression patterns were evaluated and significant differentially expressed transcripts were selected. The expression profile revealed that a response measured by the number of significant differentially expressed transcripts differed between the resistant and susceptible genotype in timing. Nine differentially expressed transcripts were successfully sequenced of which two transcripts originated from the mRNA population of the pathogen, two transcripts were derived from the susceptible cultivar of Helianthus annuus and five transcripts were isolated from the resistant genotype of Helianthus maximiliani. Semi-quantitative real-time PCR was accomplished to verify the significant differential expression of the potentially resistance-associated transcripts coumarate-CoA-ligase and cysteine protease transcript in the resistant H. maximiliani accession and differential expression of a chlorophyll-a/b-binding-protein and an S-adenosyl-methionine-synthetase transcript originating from the susceptible H. annuus cultivar. © 2010 Springer-Verlag.

Couvreur V.,Catholic University of Louvain | Vanderborght J.,Forschungszentrum Juelich GmbH | Javaux M.,Catholic University of Louvain | Javaux M.,Forschungszentrum Juelich GmbH
Hydrology and Earth System Sciences | Year: 2012

Many hydrological models including root water uptake (RWU) do not consider the dimension of root system hydraulic architecture (HA) because explicitly solving water flow in such a complex system is too time consuming. However, they might lack process understanding when basing RWU and plant water stress predictions on functions of variables such as the root length density distribution. On the basis of analytical solutions of water flow in a simple HA, we developed an "implicit" model of the root system HA for simulation of RWU distribution (sink term of Richards' equation) and plant water stress in three-dimensional soil water flow models. The new model has three macroscopic parameters defined at the soil element scale, or at the plant scale, rather than for each segment of the root system architecture: the standard sink fraction distribution SSF, the root system equivalent conductance Krs and the compensatory RWU conductance Kcomp. It clearly decouples the process of water stress from compensatory RWU, and its structure is appropriate for hydraulic lift simulation. As compared to a model explicitly solving water flow in a realistic maize root system HA, the implicit model showed to be accurate for predicting RWU distribution and plant collar water potential, with one single set of parameters, in dissimilar water dynamics scenarios. For these scenarios, the computing time of the implicit model was a factor 28 to 214 shorter than that of the explicit one. We also provide a new expression for the effective soil water potential sensed by plants in soils with a heterogeneous water potential distribution, which emerged from the implicit model equations. With the proposed implicit model of the root system HA, new concepts are brought which open avenues towards simple and mechanistic RWU models and water stress functions operational for field scale water dynamics simulation. © 2012 Author(s). CC Attribution 3.0 License.

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