How Heterogeneous Pore Scale Distributions of Wettability Affect Infiltration into Porous Media

Wettability is an important parameter that significantly determines hydrology in porous media, and it especially controls the flow of water across the rhizosphere—the soil-plant interface. However, the influence of spatially heterogeneous distributions on the soil particles surfaces is scarcely known. Therefore, this study investigates the influence of spatially heterogeneous wettability distributions on infiltration into porous media. For this purpose, we utilize a two-phase flow model based on Lattice-Boltzmann to numerically simulate the infiltration in porous media with a simplified geometry and for various selected heterogeneous wettability coatings. Additionally, we simulated the rewetting of the dry rhizosphere of a sandy soil where dry hydrophobic mucilage depositions on the particle surface are represented via a locally increased contact angle. In particular, we can show that hydraulic dynamics and water repellency are determined by the specific location of wettability patterns within the pore space. When present at certain locations, tiny hydrophobic depositions can cause water repellency in an otherwise well-wettable soil. In this case, averaged, effective contact angle parameterizations such as the Cassie equation are unsuitable. At critical conditions, when the rhizosphere limits root water uptake, consideration of the specific microscale locations of exudate depositions may improve models of root water uptake

Root and rhizosphere traits for enhanced water and nutrients uptake efficiency in dynamic environments

Modern agriculture’s goal of improving crop resource acquisition efficiency relies on the intricate relationship between the root system and the soil. Root and rhizosphere traits play a critical role in the efficient use of nutrients and water, especially under dynamic environments. This review emphasizes a holistic perspective, challenging the conventional separation of nutrient and water uptake processes and the necessity for an integrated approach. Anticipating climate change-induced increase in the likelihood of extreme weather events that result in fluctuations in soil moisture and nutrient availability, the study explores the adaptive potential of root and rhizosphere traits to mitigate stress. We emphasize the significance of root and rhizosphere characteristics that enable crops to rapidly respond to varying resource availabilities (i.e. the presence of water and mobile nutrients in the root zone) and their accessibility (i.e. the possibility to transport resources to the root surface). These traits encompass for example root hairs, mucilage and extracellular polymeric substance (EPS) exudation, rhizosheath formation and the expression of nutrient and water transporters. Moreover, we recognize the challenge of balancing carbon investments, especially under stress, where optimized traits must consider carbon-efficient strategies. To advance our understanding, the review calls for well-designed field experiments, recognizing the limitations of controlled environments. Non-destructive methods such as mini rhizotron assessments and in-situ stable isotope techniques, in combination with destructive approaches such as root exudation analysis, are proposed for assessing root and rhizosphere traits. The integration of modeling, experimentation, and plant breeding is essential for developing resilient crop genotypes capable of adapting to evolving resource limitation

Crop cover selection to improve weed control in multi-species agrosystems in Reunion Island

Cover crops are increasingly used for weed management in tropical regions as an alternative to herbicide. But selecting the most suitable species of cover crop to be associated with a main crop requires long-term trials. Here we present a two-years set of experiments to assess the ability of various cover crops to limit weed growth. First, a collection experiment of 55 species and varieties was performed to assess the life cycle of cover crops in tropical climate in Reunion Island, in three different sites. This experiment allowed us to select different cover crop species whom behavior would be adapted to the different agrosystems in Reunion Island (sugarcane in rotation or intercropping, arboriculture,…). Secondly, 10 species were selected and grown in large plots to assess their ability to limit weed growth in monospecific plots as well as mixture of cover crops. After two months of growth, the most productive cover crops showed the ability to limit weed growth to fewer than 30% of the plot (e.g. crotalaria, oat, millet…) while the less productive were unsuccessful to cope with weeds. On the contrary, all combinations of two cover crops tested in this experiment were able to limit weed growth to fewer than 30% of the plot area. Our experiment highlights some key cover crops adapted to intercropping and rotation in multispecies agrosystems as an alternative herbicide

Spatial Distribution of Mucilage in the Rhizosphere Measured With Infrared Spectroscopy

Mucilage is receiving increasing attention because of its putative effects on plant growth, but so far no method is available to measure its spatial distribution in the rhizosphere. We tested whether the C-H signal related to mucilage fatty acids is detectable by infrared spectroscopy and if this method can be used to determine the spatial distribution of mucilage in the rhizosphere. Maize plants were grown in rhizoboxes filled with soil free of organic matter. Infrared measurements were carried out along transects perpendicular as well as axially to the root channels. The perpendicular gradients of the C-H proportions showed a decrease of C-H with increasing distance: 0.8 mm apart from the root center the C-H signals achieved a level near zero. The measured concentrations of mucilage were comparable with results obtained in previous studies, which encourages the use of infrared spectroscopy to quantitatively image mucilage in the rhizosphere

Bypass and hyperbole in soil science:A perspective from the next generation of soil scientists

International audienceWe, the co‐authors of this letter, are an international group of soil scientists at early career stages, from PhD students to postdoctoral researchers, lecturers, and research fellows with permanent positions. Here, we present our collective musings on soil research challenges and opportunities and, in particular, the points raised by Philippe Baveye (Baveye, 2020a, 2020b) and Johan Bouma (Bouma, 2020) on bypass and hyperbole in soil science. Raising awareness about these issues is a first and necessary step. To this end, we would like to thank Philippe Baveye and Johan Bouma for initiating this debate.......

Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation

WEST is an MA class superconducting, actively cooled, full tungsten (W) tokamak, designed to operate in long pulses up to 1000 s. In support of ITER operation and DEMO conceptual activities, key missions of WEST are: (i) qualification of high heat flux plasma-facing components in integrating both technological and physics aspects in relevant heat and particle exhaust conditions, particularly for the tungsten monoblocks foreseen in ITER divertor; (ii) integrated steady-state operation at high confinement, with a focus on power exhaust issues. During the phase 1 of operation (2017–2020), a set of actively cooled ITER-grade plasma facing unit prototypes was integrated into the inertially cooled W coated startup lower divertor. Up to 8.8 MW of RF power has been coupled to the plasma and divertor heat flux of up to 6 MW m−2 were reached. Long pulse operation was started, using the upper actively cooled divertor, with a discharge of about 1 min achieved. This paper gives an overview of the results achieved in phase 1. Perspectives for phase 2, operating with the full capability of the device with the complete ITER-grade actively cooled lower divertor, are also described

The PLATO mission

PLATO (PLAnetary Transits and Oscillations of stars) is ESA’s M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2REarth) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5%, 10%, 10% for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO‘s target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile towards the end of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases

Impact of Pore-Scale Wettability on Rhizosphere Rewetting

Vast amounts of water flow through a thin layer of soil around the roots, the rhizosphere, where high microbial activity takes place—an important hydrological and biological hotspot. The rhizosphere was shown to turn water repellent upon drying, which has been interpreted as the effect of mucilage secreted by roots. The effects of such rhizosphere water dynamics on plant and microbial activity are unclear. Furthermore, our understanding of the biophysical mechanisms controlling the rhizosphere water repellency remains largely speculative. Our hypothesis is that the key to describe the emergence of water repellency lies within the microscopic distribution of wettability on the pore-scale. At a critical mucilage content, a sufficient fraction of pores is blocked and the rhizosphere turns water repellent. Here we tested whether a percolation approach is capable to predict the flow behavior near the critical mucilage content. The wettability of glass beads and sand mixed with chia seed mucilage was quantified by measuring the infiltration rate of water drops. Drop infiltration was simulated using a simple pore-network model in which mucilage was distributed heterogeneously throughout the pore space with a preference for small pores. The model approach proved capable to capture the percolation nature of the process, the sudden transition from wettable to water repellent and the high variability in infiltration rates near the percolation threshold. Our study highlights the importance of pore-scale distribution of mucilage in the emergent flow behavior across the rhizosphere

Impact of wettability distribution on soil rewetting

&amp;lt;p&amp;gt;Benard P.&amp;lt;sup&amp;gt;1*&amp;lt;/sup&amp;gt;, Bachmann J.&amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt;, Bundschuh U.&amp;lt;sup&amp;gt;3&amp;lt;/sup&amp;gt;, Cramer A.&amp;lt;sup&amp;gt;1&amp;lt;/sup&amp;gt;, Kaestner A.&amp;lt;sup&amp;gt;4&amp;lt;/sup&amp;gt;, Carminati A.&amp;lt;sup&amp;gt;1&amp;lt;/sup&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;sup&amp;gt;1&amp;lt;/sup&amp;gt;Physics of Soils and Terrestrial Ecosystems, Department of Environmental Systems Science, ETH Z&amp;amp;#252;rich, Universit&amp;amp;#228;tstrasse 16, 8092 Z&amp;amp;#252;rich, Switzerland&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt;Institute of Soil Science, Leibniz Universit&amp;amp;#228;t Hannover, Herrenh&amp;amp;#228;user Strasse 2, 30419 Hannover, Germany&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;sup&amp;gt;3&amp;lt;/sup&amp;gt;Soil Physics, Faculty for Biology, Chemistry, and Earth Sciences, University of Bayreuth, Universit&amp;amp;#228;tsstra&amp;amp;#223;e 30, 95447 Bayreuth, Bavaria, Germany&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;sup&amp;gt;4&amp;lt;/sup&amp;gt;Paul Scherrer Institute, Lab. for Neutron Scattering and Imaging, Forschungsstrasse 111, 5232 Villigen, Switzerland&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;*corresponding author; [email protected]&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Plant roots and microorganisms engineer soil physical properties on the pore scale. The accumulation of organic residues in forest soils and the release of exudates alter local soil wettability and by that impact soil rewetting. We captured the capillary driven infiltration of water and ethanol in forest soils and model rhizosphere using time-series neutron radiography. Information on the evolution of local soil water and ethanol content were used to estimate the distribution of wettability employing a 3D pore-network model. Estimates derived by inverse modelling were compared to classic measures of soil wettability and a set of contrasting scenarios regarding their impact on soil rewetting.&amp;lt;/p&amp;gt;</jats:p