Threshold Water Content Research Articles

Abscisic acid increase correlates with the soil water threshold of transpiration decline during drought.

By regulating carbon uptake and water loss by plants, stomata are not only responsible for productivity but also survival during drought. The timing of the onset of stomatal closure is crucial for preventing excessive water loss during drought, but is poorly explained by plant hydraulics alone and what triggers stomatal closure remains disputed. We investigated whether the hormone abscisic acid (ABA) was this trigger in a highly embolism-resistant tree species Umbellularia californica. We tracked leaf ABA levels, determined the leaf water potential and gravimetric soil water content (gSWC) thresholds for stomatal closure and transpiration decline during a progressive drought. We found that U. californica plants have a peaking-type ABA dynamic, where ABA levels rise early in drought and then decline under prolonged drought conditions. The early increase in ABA levels correlated with the closing of stomata and reduced transpiration. Furthermore, we found that transpiration declined before any large decreases in predawn plant water status and could best be explained by transient drops in midday water potentials triggering increased ABA levels. Our results indicate that ABA-mediated stomatal regulation may be an integral mechanism for reducing transpiration during drought before major drops in bulk soil and plant water status.

Irrigation expansion shows potential for increased maize yield and reduced nitrogen leaching in the Midwest US

CONTEXTYield gaps in Midwest US rainfed maize (Zea mays L.) are likely to continue to increase as the frequency of extreme weather events associated with future climate change increase (i.e., high temperatures, precipitation variability). One solution to closing this gap is the expansion of irrigation in regions that currently do not utilize this practice. While irrigation expansion has the potential to increase maize yields and crop productivity, there is also the potential to see improvement in nitrogen loss. However, it remains unclear at what point irrigation should be triggered (i.e., plant available water content (AWC) thresholds) to obtain a balance between crop productivity and environmental improvements. OBJECTIVEThe objective of this study is to assess the effects of irrigation management on maize yield, nitrogen leaching, and water use efficiency under the expansion of irrigation across the entire Midwest US and to determine the optimal plant AWC threshold to trigger irrigation for achieving a substantial increase in maize yield and reduction in nitrogen leaching while using the minimal amount of required irrigation. METHODSWe use an agroecosystem model, Agro-IBIS, to simulate both rainfed and irrigated maize production and nitrogen leaching under likely future climate conditions (i.e., wet-warm, dry-warm). To determine the optimal plant AWC threshold for irrigation, irrigation scenarios were conducted for a range of plant AWC thresholds (0.2 to 0.8) across the entire Midwest US. RESULTS AND CONCLUSIONSOur results show that Midwest US regions that do not currently utilize irrigation could experience an 11–37% increase in maize yield and a 12–32% decrease in nitrogen leaching when irrigation (39.0 to 96.8 mm yr−1) is triggered at the lower end of the plant AWC threshold (e.g., 0.3). Maize grown under dry-warm and wet-warm climate conditions will likely experience increased yields and reduced nitrogen loss with minimal irrigation. While these findings suggest that the expansion of irrigation could help close yield gaps while improving other ecosystem services, future work should focus on simulating these conditions under a wider range of precipitation extremes and fertilizer management to better understand the potential interactions under a changing climate. SIGNIFICANCEThis study outlines the optimal plant AWC threshold for irrigation to maximize maize yields in the Midwest while minimizing nitrogen loss and can provide valuable insights for making informed decisions about landscape management under future conditions.

Combined effects of rainfall‐runoff events and antecedent soil moisture on runoff generation processes in an upland forested headwater area

AbstractIn this study, we investigate the combined effect of different rainfall‐runoff event types and antecedent soil moisture (ASM) on runoff processes in the headwater elementary discharge area of a small forested upland catchment. The study focuses on (i) the relationship between soil moisture thresholds and runoff generation; (ii) the combined effect of ASM and tree vicinity and (iii) the relationship between different rainfall‐runoff event types and different types of runoff (baseflow and stormflow). The results suggest that ASM has a strong impact on local runoff generation processes. Soil water content (35%–36%) threshold exceedance was related to stormflow runoff generation caused by the activation of quick preferential flow paths in the soil during storm events, especially in the upper and the deepest soil layers. At the same time, unexpected non‐linear increases in baseflow runoff ratios were documented during dry, precipitation‐free, periods and when the 31%–34% soil moisture threshold was exceeded, presumably due to the hydrological connection of farther slope areas during these conditions. Multiple stormflow periods, which exhibited the lowest runoff coefficient, were the most significant events in terms of water retention and soil water recharge due to increased vertical hydrological connectivity enabling more rapid transport to deeper soil layers. However, this rainfall type occurred least often over the study period. The important role of forest stands (individual trees) in creating spatial patterns of soil moisture and preferential infiltration paths to deeper soil layers was also confirmed. These results contribute towards a better conceptualisation of hydrological behaviour in elementary headwater discharge areas and highlight the potential dangers associated with expected increases in extreme weather events.

Unexpectedly, triple super phosphate fertilizer induces maize drought resilience

Phosphorus fertilizer is commonly applied to soils in crop production as diammonium phosphate (DAP). To decrease ammonium addition to the environment, triple super phosphate (TSP) is being considered as a DAP replacement. This study was undertaken to compare the response of maize plants to soil fertilization with TSP vs. DAP under well-watered conditions, under soil-drying conditions, and root hydraulic conductance. It was found for well-watered conditions in a controlled environment that there was no difference in plant growth between DAP to TSP treatments. In soil dry-down experiments, however, the initiation of the decrease in transpiration rate was unexpectedly quite different between DAP and TSP treatments. The soil water content threshold for initiation of decrease in transpiration rate with DAP treatment (average fraction transpirable soil water for two experiments = 0.285) was consistent with common observations, but the threshold associated with TSP treatment occurred at an unusually high soil water content (average fraction transpirable soil water for two experiments = 0.545). The higher threshold with TSP resulted in an extended period of soil water use, i.e. soil water conservation. Soil water conservation resulting from the TSP treatment was associated with a 27% greater shoot mass accumulation following a 4-wk re-watering period after the water-deficit treatment than measured with the DAP treatment. The high threshold for decrease in transpiration resulting from TSP was consistent with measured lower root hydraulic conductance as compared to DAP treatment. The unexpected discovery of TSP-induced initiation of transpiration rate decrease at high soil water content is consistent with greater crop drought resilience.

Stability Assessment of Tunnels Excavated in Loess with the Presence of Groundwater—A Case Study

The high water content of the surrounding rock in loess tunnels will lead to the deterioration of rock strength, causing deformation and damage to the initial support structure and thereby affecting safety during construction and operation. This article first analyzes the strength characteristics of loess under different water contents through indoor physical and mechanical tests. Secondly, based on numerical simulation results, the ecological environment, and design requirements, the water content threshold is determined. Finally, a reinforcement scheme combining surface precipitation measures and curtain grouting measures is proposed, and the reinforcement effect is analyzed based on on-site monitoring data. The results show that as the water content of loess increases, the cohesion, internal friction angle, and elastic modulus of the surrounding rock all decrease, leading to an increase in the sensitivity of the surrounding rock to excavation disturbances and a deterioration in strength. During the construction process, it shows an increase in the vault settlement and sidewalls’ convergence. During the process of increasing the distance between the monitoring section and the palm face, the settlement and convergence of the tunnel show a rapid growth stage, slow growth stage, and stable stage. The water content threshold is determined to be 22%. The reinforcement scheme of combining surface precipitation measures with curtain grouting measures not only meets the requirements of the ecological environment but also makes the settlement and convergence values lower than the yellow warning deformation values required by the design.

Contrasting water-use strategies revealed by species-specific transpiration dynamics in the Caatinga dry forest.

In forest ecosystems, transpiration (T) patterns are important for quantifying water and carbon fluxes and are major factors in predicting ecosystem change. Seasonal changes in rainfall and soil water content can alter the sensitivity of sap flux density to daily variations in vapor pressure deficit (VPD). This sensitivity is species-specific and is thought to be related to hydraulic strategies. The aim of this work is to better understand how the sap flux density of species with low versus high wood density differ in their sensitivity to VPD and soil water content and how potentially opposing water-use strategies influence T dynamics, and ultimately, correlations to evapotranspiration (ET). We use hysteresis area analysis to quantify the sensitivity of species-specific sap flux density to changes in the VPD, breakpoint-based models to determine the soil water content threshold instigating a T response and multiscalar wavelet coherency to correlate T to ET. We found that low wood density Commiphora leptophloeos (Mart.) Gillett had a more dynamic T pattern, a greater sensitivity to VPD at high soil water content, required a higher soil water content threshold for this sensitivity to be apparent, and had a significant coherency correlation with ET at daily to monthly timescales. This behavior is consistent with a drought avoidance strategy. High wood density Cenostigma pyramidale (Tul.) E. Gagnon & G. P. Lewis, conversely, had a more stable T pattern, responded to VPD across a range of soil water content, tolerated a lower soil water content threshold to T, and had a significant coherency correlation with ET at weekly timescales. This behavior is consistent with a drought-tolerant strategy. We build on previous research to show that these species have contrasting water-use strategies that should be considered in large-scale modeling efforts.

Sensitivity of the MAR regional climate model snowpack to the parameterization of the assimilation of satellite-derived wet-snow masks on the Antarctic Peninsula

Abstract. Both regional climate models (RCMs) and remote sensing (RS) data are essential tools in understanding the response of polar regions to climate change. RCMs can simulate how certain climate variables, such as surface melt, runoff and snowfall, are likely to change in response to different climate scenarios but are subject to biases and errors. RS data can assist in reducing and quantifying model uncertainties by providing indirect observations of the modeled variables on the present climate. In this work, we improve on an existing scheme to assimilate RS wet snow occurrence data with the “Modèle Atmosphérique Régional” (MAR) RCM and investigate the sensitivity of the RCM to the parameters of the scheme. The assimilation is performed by nudging the MAR snowpack temperature to match the presence of liquid water observed by satellites. The sensitivity of the assimilation method is tested by modifying parameters such as the depth to which the MAR snowpack is warmed or cooled, the quantity of water required to qualify a MAR pixel as “wet” (0.1 % or 0.2 % of the snowpack mass being water), and assimilating different RS datasets. Data assimilation is carried out on the Antarctic Peninsula for the 2019–2021 period. The results show an increase in meltwater production (+66.7 % on average, or +95 Gt), along with a small decrease in surface mass balance (SMB) (−4.5 % on average, or −20 Gt) for the 2019–2020 melt season after assimilation. The model is sensitive to the tested parameters, albeit with varying orders of magnitude. The prescribed warming depth has a larger impact on the resulting surface melt production than the liquid water content (LWC) threshold due to strong refreezing occurring within the top layers of the snowpack. The values tested for the LWC threshold are lower than the LWC for typical melt days (approximately 1.2 %) and impact results mainly at the beginning and end of the melting period. The assimilation method will allow for the estimation of uncertainty in MAR meltwater production and will enable the identification of potential issues in modeling near-surface snowpack processes, paving the way for more accurate simulations of snow processes in model projections.

Circular use of fine-grained tailings to underground mine wind walls

Mining activities tend to generate various waste including tailings, waste water and waste rock. Efficient management and disposal of these waste materials are critical to minimize their environmental impact and ensure the sustainable operation of mining activities. A huge number of tailings are produced all around the world each year. Generally, part of the tailings is used for underground backfilling and another part is discharged to the tailings dam. The former can provide underground support while the latter tends to cause some environmental problems because the tailings are generally mixed with some chemicals. Regarding this, enhancing the circular use of tailings is crucial to guarantee the sustainable mining engineering. In this study, the feasibility of using fine-grained tailings to make non-burning hollow bricks for underground windbreaks is investigated. A two-stage experiment was implemented where the first stage experiment indicated the threshold of water content, the ratio of cement and tailings and the ratio of fine-grained and rod-mill tailings. In addition, it can be indicated that the addition of polyethylene fibers would increase the compressive strength of hollow bricks in some extent. The second-stage experiment was conducted with no rod-mill tailing added and it can be found that when the ratio of cement and tailings is equal or higher than 1:6, fiber content is more significant in improving brick strength but when this value is lower, the ratio of cement is more important than fiber factors. When the ratio of cement and fine-grained tailings is 1:8 with 0.5 g/kg and 12 mm polypropylene fiber added, the hollow brick is capable of achieving strength of 1.4 MPa for 28 days curation with the price of 0.50 RMB/block. This proportioning scheme is the least expensive while meeting the strength of the windbreak wall for the Fan Kou lead–zinc mine. Finally, it can be indicated that the usage of fine-grained tailings to make underground windbreak wall is feasible and thus provide a new scenario to circular usage of tailings. In addition, other proportioning schemes proposed in this study perhaps can meet more engineering requirements so as to provide more alternatives for circular use of tailings.

Study on Disintegration and Infiltration Characteristics of Nanjing Jiangxinzhou Embankment Soil

Flood season embankment due to long-term high water immersion environment creates situations where its soil properties will deteriorate, quickly triggering bank slope instability and other dangerous situations. In order to study embankment slope soil in the disintegration and permeability characteristics under the long-term water immersion process, disintegration tests and variable head infiltration tests were carried out on embankment-disturbed clays in Jiangxinzhou, Nanjing, Jiangsu Province, China. The results showed that the disintegration rate decreased with increasing dry density. Moreover, the samples gained weight quickly when the water content was low. Moreover, there is a threshold water content of around 20%, and it is assumed that the disintegration pattern of the soil may be significantly different depending on the optimum moisture content. The effect of moisture content on the disintegration of the samples was more significant. There were three main typical disintegration modes of the samples. The primary influencing factors resulting in the various disintegration patterns are the soil matrix suction, the change in consistency following water immersion, and the water membrane on the surface of the clay particles. The coefficient of permeability decreases with increasing dry density, and the variation of the coefficient of permeability with dry density coincides with the exponential function relationship. Long-term immersion conditions will change the permeability of the soil. An electron microscope test of immersed and unimmersed samples shows that the internal structure change is an essential factor affecting the permeability. After water immersion, with the dissolution of cementing material between soil particles, the particles move to fill the intergranular pore space so that the permeability coefficient decreases.

Effectiveness of Bio Activator of Phosphate Solubilizing Bacteria Consortium on Composting Bag-log Waste Incorporated with Cow Dung

Bag-log waste is an organic material that is difficult to decompose. This is due to the bag log's high content of lignin compounds. Therefore, to speed up the composting process, it is necessary to include other organic materials and bio activators. This study aims to analyze the effectiveness of the bio-activator consortium of Phosphate Dissolving Bacteria (KBPF) in composting bag-log waste mixed with cow dung. The experiment consisted of 5 treatments with three replications, namely (T1) bag-log waste, (T2) a mixture of bag-log waste and cow manure with a composition of 1:2 (wt/wt), (T3) a mixture of bag-log waste and cow manure with 2:1 ( wt/wt), (T4) a mixture of bag-log waste and cow manure with a composition of 1:2 (wt/wt) plus KBPF (200 ml) with a density of 108 CFU/ml (T5) a mixture of bag-log waste and cow manure with a composition of 2:1 (wt/wt) plus KBPF (200 ml) with a density of 108 CFU/ml. The experiment was created as - Completely Randomized Design (CRD). The experimental results show that bag-log waste cannot be decomposed fastly without cow dung and bio activators. The treatments of T2, T3, T4 and T5 produced compost with quality not significantly different from one another. Under these treatments, the temperature was controlled in the mesophilic stage, and the composting pH was returned to neutral, while the moisture content and C/N ratio decreased to almost half of their original levels at the end of the composting period. It seems that inoculation of KBPF into the mixture of cow dung and bag-log waste has no role in accelerating the composting process. The mix of Bag-log and cow dung, with a minimal proportion of 2:1 without inoculation KBPF, was the recommended combination in composting bag-log in which the final product (compost) could fulfil its pH (neutral), the threshold of temperature and water content. The C/N ratio of the treatment was close C/N ratio of mature compost, and total N and total P contents were more than the standard of SNI 19-7030-2004.

Thermophysical Properties of Bentonite–Sand/Fly Ash-Based Backfill Materials for Underground Power Cable

The surrounding (backfill) materials around the underground power cable systems are essential for dissipating the heat away from it, during the exertion phases. The heat dissipation restrains the thermal instability and risk of progressive drying of the backfill materials, thus reducing the thermal stress on the power cable. Thermal instability indicates the reduction in thermal properties (conductivity or diffusivity) due to the migration of moisture because of heat accumulation. Thus, the backfill materials should have adequate thermal properties and water retention capacity to transfer the heat from the heat source to the surrounding area with minimal moisture migration. The bentonite has high water retention capacity, but low thermal conductivity, whereas sand/fly ash exhibits low water retention and has higher thermal conductivity than bentonite. The addition of bentonite promotes the water holding capacity and thermophysical properties of sand and fly ash. Therefore, this study presents the thermal properties of backfill materials, bentonite–fly ash (B–F) and bentonite–sand (B–S), at varying weight-percent of sand and fly ash with bentonite. Various compositions of the mixtures were compacted to varying dry densities, and water contents and thermal properties variation of backfill materials were measured using a dual thermal needle probe ‘KD2 Pro’ at room temperature. The study deals with the systematic evaluation of the volumetric specific heat capacity, thermal conductivity, and diffusivity of backfill materials against varying dry density and water content. The threshold water content (TWC) has been determined from the thermal diffusivity–water content variation curve, and it has correlated with plastic limit (PL) and optimum moisture content (OMC). Thereafter, the efficacies of two thermal conductivity prediction models have also been evaluated statistically with respect to experimental results.

Effect of soil water content threshold on kiwifruit quality at different growth stages with drip irrigation in the humid area of Southern China

• Effects of soil water content threshold (SWCT) on kiwifruit quality depended on SWCT timing and degree. • SWCT of 55% field capacity (FC) increased fruit volume and fruit weight at bud burst to leafing stage. • SWCT of 65% FC elevated total soluble solids, soluble sugar and solid-acid ratio at fruit growth stage. • SWCT of 60% FC improved firmness, total soluble solids, soluble sugar, vitamin C and solid-acid ratio at fruit maturation stage. Fruit quality as affected by soil water content threshold levels (SWCT) at different growth stages remains largely elusive. Therefore, a drip irrigation experiment was conducted to investigate the effect of SWCT on kiwifruit quality at bud burst to leafing stage (stage I), flowering to fruit set stage (stage II), fruit growth stage (stage III) and fruit maturation stage (stage IV) during 2018 and 2019 in the humid area of southern China, respectively. The results showed that SWCT at stage I mainly affected fruit weight (Fw). I-55% treatment significantly elevated Fw by 11.6%-8.0% ( P < 0.05). SWCT at stage II had little effect on fruit quality. SWCT at stage III influenced fruit volume (Fv) and chemical quality. Specifically, Fv was increased by 8.0%-2.2% under III-75% treatment, total soluble solids (TSS), soluble sugar (SS) and solids-acid ratio (SOAR) were increased by 9.4%-10.0% ( P < 0.05), 2.4%-5.8% and 7.9%-10.6% ( P < 0.05) under III-65% treatment, respectively. SWCT at stage IV impacted fruit firmness (Fn) and chemical quality. IV-60% treatment increased Fn, TSS, SS, VC and SOAR by 5.6%-10.5%, 12.0%-12.6% ( P < 0.05), 6.6%-9.1% ( P < 0.05), 2.1%-14.0% ( P < 0.05), and 8.1%-8.3% ( P < 0.05), respectively, which was beneficial to the improvement of nutritional value and taste, and also the storage and transportation of kiwifruit. Collectively, SWCT of 55% FC (field capacity) at stage I or 65% FC at stage III or 60% FC at stage IV was an effective measure to improve the kiwifruit quality.

Influence of varying water content on permanent deformation of mud-fouled ballast

The contamination of ballast by mud pumping is known to cause considerable reduction in the shear resistance as well as increased settlement of railroad foundations. However, how varying water content (w) of fouled ballast can affect this deterioration has not been properly understood. The current study thus adopts a large-scale cyclic triaxial test to examine permanent (plastic) deformation of mud-fouled ballast collected from a site with a history of mud pumping with a consideration of different water contents. In these tests, fouling content varies from 5 to 30 %, while the water content changes from 0 to 40 %. The results show that while increasing content of fines causes larger permanent settlement of ballast, varying water content of fines can influence this behaviour significantly. A salient finding of this study is the critical threshold of water content near to the liquid limit (LL) of fine soil (finer than 0.425 mm) that can cause a swift increase in ballast settlement. The results show that the peak permanent strain can increase by about 26 % compared to the dry state when w of fines reaches the LL. On the other hand, permanent strain of fouled ballast can decrease at the optimum water content of fines, if a sufficient mass of fines (>20 % by weight) is provided to reinforce the granular assembly. An empirical method is provided to estimate the ultimate settlement of mud-fouled tracks considering the moisture state that would be most beneficial in real-life applications.

Prediction of Soil Water Thresholds for Trees in the Semi-Arid Region on the Loess Plateau

It is important to obtain the soil water content threshold (θTHR) for agricultural water management. However, the measurement of θTHR is time consuming and needs specialized and expensive equipment. The accuracy of the empirical estimates is often low. Therefore, the development of a simple, rapid, and accurate prediction method for θTHR is the focus of the present study. The value of θTHR is regarded as the soil water content at the capillary break capacity (θCB). A formula based on field capacity (θFC) and soil bulk density (Db) is proposed to calculate θCB, expressed as θCB=θFC−0.21*1−Db/2.65. Six soils from six published studies on the response of tree physiological processes to water deficit were used to calculate θCB using this formula. The calculated θCB values were compared with the measured θTHR. The results showed that the calculated θCB values were nearly equal to the measured θTHR. A highly significant (adj R2 = 0.9826, p &lt; 0.001) linear relationship with a slope of 0.9506 and a y intercept of 0.0072 was found between the calculated θCB and measured θTHR. The formula proposed in this study provides a novel approach for estimating the θTHR of trees in the semi-arid regions on the Loess Plateau.

Critical water contents at leaf, stem and root level leading to irreversible drought-induced damage in two woody and one herbaceous species.

Plant water content is a simple and promising parameter for monitoring drought-driven plant mortality risk. However, critical water content thresholds leading to cell damage and plant failure are still unknown. Moreover, it is unclear whether whole-plant or a specific organ water content is the most reliable indicator of mortality risk. We assessed differences in dehydration thresholds in leaf, stem and root samples, hampering the organ-specific rehydration capacity and increasing the mortality risk. We also tested eventual differences between a fast experimental dehydration of uprooted plants, compared to long-term water stress induced by withholding irrigation in potted plants. We investigated three species with different growth forms and leaf habits i.e., Helianthus annuus (herbaceous), Populus nigra (deciduous tree) and Quercus ilex (evergreen tree). Results obtained by the two dehydration treatments largely overlapped, thus validating bench dehydration as a fast but reliable method to assess species-specific critical water content thresholds. Regardless of the organ considered, a relative water content value of 60% induced significant cell membrane damage and loss of rehydration capacity, thus leading to irreversible plant failure and death.

Improved runoff simulations for a highly varying soil depth and complex terrain watershed in the Loess Plateau with the Community Land Model version 5

Abstract. This study aimed to improve runoff simulations and explore deep soil hydrological processes for a watershed in the center of the Loess Plateau (LP), China. This watershed, the Wuding River Basin (WRB), has very complex topography, with soil depths ranging from 0 to 197 m. The hydrological model used for our simulations was Community Land Model version 5 (CLM5) developed by the National Center for Atmospheric Research. Actual soil depths and river channels were incorporated into CLM5 to realistically represent the physical features of the WRB. Through sensitivity tests, CLM5 with 150 soil layers with the observed variable soil depths produced the most reasonable results and was adopted for this study. Our results showed that CLM5 with actual soil depths significantly suppressed unrealistic variations of the simulated subsurface runoff when compared to the default simulations. In addition, when compared with the default version with 20 soil layers, CLM5 with 150 soil layers slightly improved runoff simulations but generated simulations with much smoother vertical water flows that were consistent with the uniform distribution of soil textures in our study watershed. The runoff simulations were further improved by the addition of river channels to CLM5, where the seasonal variability of the simulated runoff was reasonably captured. Moreover, the magnitude of the simulated runoff remarkably decreased with increased soil evaporation by lowering the soil water content threshold, which triggers surface resistance. The lowered threshold was consistent with the loess soil, which has a high sand component. Such soils often generate stronger soil evaporation than soils dominated by clay. Finally, with the above changes in CLM5, the simulated total runoff matched very closely with observations. When compared with those for the default runoff simulations, the correlation coefficient, root mean square error, and Nash–Sutcliffe coefficient for the improved simulations changed dramatically from 0.02, 10.37 mm, and −12.34 to 0.62, 1.8 mm, and 0.61. The results in this study provide strong physical insight for further investigation of hydrological processes in complex terrain with deep soils.

Viability markers for determination of desiccation tolerance and critical stages during dehydration in Selaginella species.

While most plants die below a threshold of water content, desiccation-tolerant species display specific responses that allow them to survive extreme dehydration. Some of these responses are activated at critical stages during water loss and could represent the difference between desiccation tolerance (DT) and death. Here, we report the development of a simple and reproducible system to determine DT in Selaginella species. The system is based on exposure of excised tissue to a dehydration agent inside small containers, and subsequent evaluation for tissue viability. We evaluated several methodologies to determine viability upon desiccation including: triphenyltetrazolium chloride (TTC) staining, the quantum efficiency of PSII, antioxidant potential, and relative electrolyte leakage. Our results show that the TTC test is a simple and accurate assay to identify novel desiccation-tolerant Selaginella species, and can also indicate viability in other desiccation-tolerant models (i.e. ferns and mosses). The system we developed is particularly useful to identify critical points during the dehydration process. We found that a desiccation-sensitive Selaginella species shows a change in viability when dehydrated to 40% relative water content, indicating the onset of a critical condition at this water content. Comparative studies at critical stages could provide a better understanding of DT mechanisms and unravel insights into the key responses to survive desiccation.

Water Distribution on Protein Surface of the Lyophilized Proteins With Different Topography Studied by Molecular Dynamics Simulations

Water play an important role in many structural and physicochemical properties of lyophilized proteins. Molecular dynamics simulations were employed to study the explicit water distributions on four structurally diversed proteins: insulin-like growth factor 1 (IGF1), immunoglobin G1 (IgG1), human serum albumin (HSA), and collagen. The MD simulations were combined with the literature data on water vapor sorption isotherms. To account for the heterogeneity of protein surface, the water molecules were classified into different groups according to the binding strengths. A mechanistic mathematical model was built to describe the type-II vapor sorption isotherms and successfully applied to all four model protein systems. Although commonly used Brunauer-Emmett-Teller (BET) theory has a good fitting to the experimental vapor sorption isotherms, the basic “monolayer” concept is not consistent with reality – covering too limited protein surface. Experimentally, several physicochemical properties did show a break point near the BET “monolayer” level. This study demonstrates that the water content threshold or BET “monolayer” is consistent with the onset of water cluster (n≥3) formation. Based on water distributions at different amino acid sidechains as well as the backbones, a simple formula was derived based on primary sequence and fractions of ordered secondary structures (i.e. alpha helix and beta sheet) to predict the BET “monolayer”. We find that proteins with helical structural elements are more stable upon changes in water content compared to other protein architectures.

Hemispheric contrasts in ice formation in stratiform mixed-phase clouds: disentangling the role of aerosol and dynamics with ground-based remote sensing

Abstract. Multi-year ground-based remote-sensing datasets were acquired with the Leipzig Aerosol and Cloud Remote Observations System (LACROS) at three sites. A highly polluted central European site (Leipzig, Germany), a polluted and strongly dust-influenced eastern Mediterranean site (Limassol, Cyprus), and a clean marine site in the southern midlatitudes (Punta Arenas, Chile) are used to contrast ice formation in shallow stratiform liquid clouds. These unique, long-term datasets in key regions of aerosol–cloud interaction provide a deeper insight into cloud microphysics. The influence of temperature, aerosol load, boundary layer coupling, and gravity wave motion on ice formation is investigated. With respect to previous studies of regional contrasts in the properties of mixed-phase clouds, our study contributes the following new aspects: (1) sampling aerosol optical parameters as a function of temperature, the average backscatter coefficient at supercooled conditions is within a factor of 3 at all three sites. (2) Ice formation was found to be more frequent for cloud layers with cloud top temperatures above -15∘C than indicated by prior lidar-only studies at all sites. A virtual lidar detection threshold of ice water content (IWC) needs to be considered in order to bring radar–lidar-based studies in agreement with lidar-only studies. (3) At similar temperatures, cloud layers which are coupled to the aerosol-laden boundary layer show more intense ice formation than decoupled clouds. (4) Liquid layers formed by gravity waves were found to bias the phase occurrence statistics below -15∘C. By applying a novel gravity wave detection approach using vertical velocity observations within the liquid-dominated cloud top, wave clouds can be classified and excluded from the statistics. After considering boundary layer and gravity wave influences, Punta Arenas shows lower fractions of ice-containing clouds by 0.1 to 0.4 absolute difference at temperatures between −24 and -8∘C. These differences are potentially caused by the contrast in the ice-nucleating particle (INP) reservoir between the different sites.

The \u2018excess gas\u2019 method for laboratory formation of methane hydrate-bearing sand: geotechnical application

Over recent years, there has been a growing interest in producing methane gas from hydrate-bearing sands (MHBS) located below the permafrost in arctic regions and offshore within continental margins. Geotechnical stability of production wellbores is one of the significant challenges during the gas extraction process. The vast majority of geotechnical investigations of MHBS have been conducted on laboratory-formed samples due to the complex procedure of undisturbed sample extraction. One of the most commonly used hydrate laboratory-formation methods is the excess-gas method. This work investigates fundamental aspects in the excess-gas formation of MHBS that are affecting the geotechnical interpretation and modeling. The work finds that (1) the measured temperature in the experimental system may be quite different from the in-sample temperature, and can reach 4 ^circC difference during thermodynamic processes. This potential difference must be considered in investigation of hydrate formation or dissociation, (2) various calculation approaches may yield different hydrate saturation values of up to tens of percentages difference in high hydrate saturations. The calculation formulas are specified together with the fundamental difference between them, (3) the water mixture method during the sample assembling is critical for homogeneous MHBS laboratory formation, in which a maximum initial water content threshold of 9.1 to 1.3 % are obtained for a minimal fraction size of 0.01 to 0.8 mm, respectively, (4) the hydrate formation duration may influence the MHBS properties, and should be rigorously estimated according to the real-time gas consumption convergence. The outcomes of this work may contribute to the integration of data sets derived from various experiments for the study of MHBS mechanical behavior.