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The Robert  H Smith Faculty
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Publications

2019
Kessouri, P. ; Furman, A. ; Huisman, J. A. ; Martin, T. ; Mellage, A. ; Ntarlagiannis, D. ; Bücker, M. ; Ehosioke, S. ; Fernandez, P. ; Flores-Orozco, A. ; et al. Induced polarization applied to biogeophysics: recent advances and future prospects. Near Surface Geophysics 2019, 17, 595-621. Publisher's VersionAbstract
This paper provides an update on the fast-evolving field of the induced polarization method applied to biogeophysics. It emphasizes recent advances in the understanding of the induced polarization signals stemming from biological materials and their activity, points out new developments and applications, and identifies existing knowledge gaps. The focus of this review is on the application of induced polarization to study living organisms: soil microorganisms and plants (both roots and stems). We first discuss observed links between the induced polarization signal and microbial cell structure, activity and biofilm formation. We provide an up-to-date conceptual model of the electrical behaviour of the microbial cells and biofilms under the influence of an external electrical field. We also review the latest biogeophysical studies, including work on hydrocarbon biodegradation, contaminant sequestration, soil strengthening and peatland characterization. We then elaborate on the induced polarization signature of the plant-root zone, relying on a conceptual model for the generation of biogeophysical signals from a plant-root cell. First laboratory experiments show that single roots and root system are highly polarizable. They also present encouraging results for imaging root systems embedded in a medium, and gaining information on the mass density distribution, the structure or the physiological characteristics of root systems. In addition, we highlight the application of induced polarization to characterize wood and tree structures through tomography of the stem. Finally, we discuss up- and down-scaling between laboratory and field studies, as well as joint interpretation of induced polarization and other environmental data. We emphasize the need for intermediate-scale studies and the benefits of using induced polarization as a time-lapse monitoring method. We conclude with the promising integration of induced polarization in interdisciplinary mechanistic models to better understand and quantify subsurface biogeochemical processes. © 2019 European Association of Geoscientists & Engineers
Kuzma, T. ; Schwartz, N. ; Smith, R. H. Spectral induced polarization of roots in hydroponic solution and soil. In 2018 SEG International Exposition and Annual Meeting, SEG 2018; 2018 SEG International Exposition and Annual Meeting, SEG 2018; 2019; pp. 2566-2570. Publisher's VersionAbstract
Monitoring plant root within the subsurface is important but challenging, due to the opacity of the soil. Recently, it was demonstrated that the spectral induced polarization (SIP) method has the potential to image roots, but the mechanisms governing the SIP signal of roots remain poorly understood. Here, we present a numerical model and experimental setup that was designed to establish relationships between root properties and the SIP response and to enhance our understanding of the polarization mechanisms of roots. Our preliminary results show a positive correlation between root mass and quadrature conductivity in nutrient solution. Surprisingly, a negative relation was found in soil. Overall, the results from this study further demonstrate the potential of the SIP method to monitor roots. © 2018 SEG.
2018
Golan, G. ; Hendel, E. ; Méndez Espitia, G. E. ; Schwartz, N. ; Peleg, Z. Activation of seminal root primordia during wheat domestication reveals underlying mechanisms of plant resilience. Plant Cell Environ 2018, 41, 755-766.Abstract
Seminal roots constitute the initial wheat root system and provide the main route for water absorption during early stages of development. Seminal root number (SRN) varies among species. However, the mechanisms through which SRN is controlled and in turn contribute to environmental adaptation are poorly understood. Here, we show that SRN increased upon wheat domestication from 3 to 5 due to the activation of 2 root primordia that are suppressed in wild wheat, a trait controlled by loci expressed in the germinating embryo. Suppression of root primordia did not limit water uptake, indicating that 3 seminal roots is adequate to maintain growth during seedling development. The persistence of roots at their primordial state promoted seedling recovery from water stress through reactivation of suppressed primordia upon rehydration. Our findings suggest that under well-watered conditions, SRN is not a limiting factor, and excessive number of roots may be costly and maladaptive. Following water stress, lack of substantial root system suppresses growth and rapid recovery of the root system is essential for seedling recovery. This study underscores SRN as key adaptive trait that was reshaped upon domestication. The maintenance of roots at their primordial state during seedling development may be regarded as seedling protective mechanism against water stress.
2016
Schwartz, N. ; Carminati, A. ; Javaux, M. The impact of mucilage on root water uptake—A numerical study. Water Resources Research 2016, 52, 264-277. Publisher's VersionAbstract
Abstract The flow of water between soil and plants follows the gradient in water potential and depends on the hydraulic properties of the soil and the root. In models for root water uptake (RWU), it is usually assumed that the hydraulic properties near the plant root (i.e., in the rhizosphere) and in the bulk soil are identical. Yet a growing body of evidence has shown that the hydraulic properties of the rhizosphere are affected by root exudates (specifically, mucilage) and markedly differ from those of the bulk soil. In this work, we couple a 3-D detailed description of RWU with a model that accounts for the rhizosphere-specific properties (i.e., rhizosphere hydraulic properties and a nonequilibrium relation between water content and matric head). We show that as the soil dries out (due to water uptake), the higher water holding capacity of the rhizosphere results in a delay of the stress onset. During rewetting, nonequilibrium results in a slower increase of the rhizosphere water content. Furthermore, the inverse relation between water content and relaxation time implies that the drier is the rhizosphere the longer it takes to rewet. Another outcome of nonequilibrium is the small fluctuation of the rhizosphere water content compared to the bulk soil. Overall, our numerical results are in agreement with recent experimental data and provide a tool to further examine the impact of various rhizosphere processes on RWU and water dynamics.