Mechanism of Moisture Adsorption In Plant Fibers Surface-Modified With Glycerol Evaluated By LF-NMR Relaxation Technique

Surface modification by humectants is an important technology to improve product quality in textile field, healthcare, tobacco processing and paper-making industry. As a common humectant glycerol is applied to keep the moisture adsorbability of plant fibers during manufacturing. The effects of glycerol on the moisture adsorption of plant fibers were studied by analysising the induced differences of bulk and surface physicochemical property with XRD, FTIR, SEM characterizations. The improvement of moisture adsorption capacity of the modified plant fibers was due to the increased active adsorption sites, while the moisture diffusion resistance increased simultaneously with glycerol indicated by a declining Deff. LF-NMR relaxation spectra demonstrated the water sates and distributions in plant fibers were changed by loading glycerol. The moisture transfer mechanisms induced by glycerol were also investigated. Free water failed to materialize in the plant fibers treated with glycerol, immobile water existed preferentially during the adsorption, and bound water presented increasing after the immobile water were saturated. These findings are useful to improve the manufacturing processes of moisture-retaining properties of different functional plant fibers.

Insight into the Effect of Ice Addition on the Gel Properties of Nemipterus virgatus Surimi Gel Combined with Water Migration

The effect of the amount of ice added (20–60%) on the gel properties and water migration of Nemipterus virgatus surimi gel obtained with two-stage heat treatment was studied. The gel strength and water-holding capability (WHC) of the surimi gel with 30% ice added were significantly higher than those of other treatment groups (p < 0.05). The addition of 30% ice was conducive to the increase of protein β-sheet proportion during heat treatment, exposing more reactive sulfhydryl groups. These promoted the combination of protein-protein through disulfide bonds and hydrophobic-hydrophobic interactions, forming an ordered three-dimensional gel network structure. Meanwhile, the increase in hydrogen bonds promoted the protein-water interaction. Low-field nuclear magnetic resonance analysis showed that more bound water was locked in the gel system, reducing the migration of immobile water to free water and finally showing better gel properties. When the amount of ice added was insufficient (20%), the gel structure lacked the support of immobile water, resulting in deterioration of gel strength. However, excessive addition of ice (>30%) was not conducive to the combination of protein-protein and protein-water, forming a large and rough gel structure, resulting in the migration of immobile water to free water and ultimately exhibited weak gel properties.

Root Exudates Alters Nutrient Transport in Soil

&lt;p&gt;Root exudates affect the physical properties of the rhizosphere, but how these changes affect its solute transport properties is unknown. Understanding how exudates affect the rhizosphere&amp;#8217;s transport properties could advance the knowledge on nutrient dynamics in soil and its availability to plants. In the current study, we tested the effects of two exudates (chia mucilage and wheat root exudates) on the transport of iodide and potassium in soil. Solute breakthrough experiments, conducted in saturated loamy sand or coarser textured quartz sand, revealed that increasing the exudate concentration in soil results in increasingly non-equilibrium transport of both solutes. This was demonstrated by an initial solute breakthrough at a lower pore volume, followed by the arrival of the peak solute concentration at a higher pore volume. These patterns were more pronounced in soil mixed with mucilage, and in the quartz sand. An equilibrium or a physical non-equilibrium mobile-immobile transport model, fitted to the measured results, indicated an increase in the fraction of immobile water when increasing the exudates&amp;#8217; concentration in soil. For example, the estimated fraction of immobile water was up from 0 in quartz sand without exudates to 0.75 at a mucilage concentration of 0.2% in quartz sand. The solutes&amp;#8217; breakthrough under variably saturated conditions was also altered by the exudates, demonstrated by higher amounts of the solutes measured per volume of water extracted from soil mixed with exudates, compared to soil without exudates. The results indicate that exudates have a major effect on the rhizosphere&amp;#8217;s transport properties, most likely since in its presence low-conducting flow paths are formed, resulting in a physical non-equilibrium during solute transport.&lt;/p&gt;

Simulating preferential flow in a two water worlds framework

&lt;p&gt;Ecohydrological separation has been observed across climates and biomes, and at a fundamental level suggests that water in mobile versus immobile domains may resist mixing over varying periods of time; however little mechanistic evidence exists to explain this separation at a process scale. Non-equilibrium flow in the vadose zone may partially account for widespread perception of distinct hydrological domains yet no studies have weighed its contribution. Using a simple isotope mixing technique, we sought to determine the amount of preferential flow necessary to maintain a two water worlds scenario (i.e., physical separation between mobile and immobile water pools). We constructed 60 cm soil columns (20 cm-ID PVC) containing low soil structure (sieved soil material), subsoil structure (intact B horizon), and soil structure without matrix exchange (tubing reinforced macropores) to simulate multiple preferential flow scenarios. Columns were subjected to 3 rain storms of varying rainfall intensity (~2.5 cm h &lt;sup&gt;-1&lt;/sup&gt;, ~5 cm h &lt;sup&gt;-1&lt;/sup&gt;, and ~11 cm h &lt;sup&gt;-1&lt;/sup&gt;) whose stable isotope signatures oscillated around known baseline values. Isotopic analysis was performed on collected leachate and matrix water sampled via direct vapor equilibration. Preliminary estimates of matrix water indicate up to 100% mixing with infiltrating rain water under low rainfall intensity (2.5 cm h &lt;sup&gt;-1&lt;/sup&gt;) in subsoil structure columns, whereas high intensity rain (11 cm h&lt;sup&gt;-1&lt;/sup&gt;) produced clear separation between columns with intact or artificial soil structure and those controlled for structure (low structure treatment). This separation was confirmed by preferential flow estimates; however minimizing matrix exchange (via artificial macropores) reduced preferential flow by a factor of 4 compared to soil with intact structure. These data suggest that distinct domain separation may only be possible under extreme precipitation intensity; and that exchange with less mobile storage in the soil matrix produces more preferential flow. We intend to use these estimates of preferential flow as a benchmark to understand the prevalence, persistence, and plausibility of ecohydrological separation. As a next step, we will use this conceptual framework to define how recurrent drought, elevated CO&lt;sub&gt;2&lt;/sub&gt;, and warming may alter the partitioning of mobile and immobile water in mountain grasslands.&lt;/p&gt;

Inverting stop-flow leaching experiments and detection of physical and chemical non-equilibria

&lt;p&gt;Flow heterogeneity strongly impacts mass transport. In particular, the presence of water fractionation into mobile and immobile water fractions may affect pollutant sorption to soil particles. Indeed, before sorbing, the pollutants need to diffuse from mobile water to immobile water fractions. In a previous study, we investigated the possibility of stop-flow experiments for the detection of physical and chemical non-equilibria. A sensitivity analysis proved that it was possible to detect the two types of non-equilibria. The effect of parameters related to physical&amp;#160; (mobile water fraction and solute exchange rate)&amp;#160; and chemical (chemical kinetics) non-equilibria were varied and related impacts on the shape of the breakthrough curves were characterized for stop-flow experiments. However, the feasibility of inverting procedures was not investigated at all. In particular, the estimation of these parameters by fitting the model to real experimental data (with noise) may be feasible but may also bring some uncertainty with biased and non-unique estimates. In this study, using both numerically generated data and experimental data, we characterize the estimate uncertainty and equifinality. This study will help in optimizing the inverting procedure for the design of more robust and less biased estimates and the quantification of physical and chemical non-equilibria parameters.&lt;/p&gt;

A Comparative Study of Water and Bromide Transport in a Bare Loam Soil Using Lysimeters and Field Plots

The purpose of this methodological study was to test whether similar soil hydraulic and solute transport properties could be estimated from field plots and lysimeter measurements. The transport of water and bromide (as an inert conservative solute tracer) in three bare field plots and in six bare soil lysimeters were compared. Daily readings of matric head and volumetric water content in the lysimeters showed a profile that was increasingly humid with depth. The hydrodynamic parameters optimized with HYDRUS-1D provided an accurate description of the experimental data for both the field plots and the lysimeters. However, bromide transport in the lysimeters was influenced by preferential transport, which required the use of the mobile/immobile water (MIM) model to suitably describe the experimental data. Water and solute transport observed in the field plots was not accurately described when using parameters optimized with lysimeter data (cross-simulation), and vice versa. The soil’s return to atmospheric pressure at the bottom of the lysimeter and differences in tillage practices between the two set-ups had a strong impact on soil water dynamics. The preferential flow of bromide observed in the lysimeters prevented an accurate simulation of solute transport in field plots using the mean optimized parameters on lysimeters and vice versa.