Water Fluctuations Research Articles

Xylem anatomical structure as a determinant of hydraulic trait variation in C3 plant Reaumuria soongorica and C4 plant Salsola passerina

Moisture variation significantly impacts hydraulic traits and xylem anatomical structure in woody plants, thereby influencing water transport and embolism resistance. However, the precise relationship between these factors within desert shrubs remains unclear, and it may be related to plant functional types. We conducted a water manipulation experiment involving seedlings of the C3 plant Reaumuria soongorica and the C4 plant Salsola passerina within a rain shelter. We applied three water treatments: control, chronic drought, and flash drought. After a period of drought treatment, seedlings were rewatered to control level for 15 days, after which hydraulic traits and anatomical structures were measured. We found that: (1) vessel density was positively correlated with sapwood specific conductivity for R. soongorica, while hydraulic weighted vessel diameter positively correlated with embolism resistance; both hydraulic weighted vessel diameter and vessel internal diameter span was positively correlated with sapwood specific conductivity for S. passerina; (2) R. soongorica had lower edge density yet higher modularity compared to S. passerina; (3) sapwood and leaf specific conductivity emerged as hub traits in R. soongorica, while vessel internal diameter span was identified as a hub trait in S. passerina, thus serving as important predictors of hydraulic function and related attributes. Our study demonstrates distinct hydraulic strategies in the two species. R. soongorica employs a highly modular trait combination to adapt to water fluctuations, maintaining both high hydraulic efficiency and embolism resistance under drought stress. Conversely, S. passerina integrates traits for efficient resource access, ensuring hydraulic efficiency but compromising embolism resistance under drought stress. Integrating hydraulic traits with anatomical structures significantly enhances predictions of desert shrub resilience to drought within the context of global climate change.

A novel approach for multivariate time series interval prediction of water quality at wastewater treatment plants.

This study proposes a novel approach for predicting variations in water quality at wastewater treatment plants (WWTPs), which is crucial for optimizing process management and pollution control. The model combines convolutional bi-directional gated recursive units (CBGRUs) with adaptive bandwidth kernel function density estimation (ABKDE) to address the challenge of multivariate time series interval prediction of WWTP water quality. Initially, wavelet transform (WT) was employed to smooth the water quality data, reducing noise and fluctuations. Linear correlation coefficient (CC) and non-linear mutual information (MI) techniques were then utilized to select input variables. The CBGRU model was applied to capture temporal correlations in the time series, integrating the Multiple Heads of Attention (MHA) mechanism to enhance the model's ability to comprehend complex relationships within the data. ABKDE was employed, supplemented by bootstrap to establish upper and lower bounds of the prediction intervals. Ablation experiments and comparative analyses with benchmark models confirmed the superior performance of the model in point prediction, interval prediction, the analysis of forecast period, and fluctuation detection for water quality data. Also, this study verifies the model's broad applicability and robustness to anomalous data. This study contributes significantly to improved effluent treatment efficiency and water quality control in WWTPs.

How the vertical gradient of light in the understorey and water seasonality affect leaf traits of Vanilla phaeantha (Orchidaceae), a crassulacean acid metabolism (CAM) hemiephyte.

Structural and physiological leaf traits and their plasticity were compared in the hemiepiphyte Vanilla phaeantha . This species grows along a phorophyte reaching different understorey positions and exhibiting diverse responses to environment changes. We analysed three height strata above the ground, establishing a light gradient, and considering seasonal water fluctuations. The upper leaves had higher area and mass and were less pigmented. The dry season induced a reduction of approximately 2h of stomatal opening over the diel 24h crassulacean acid metabolism (CAM) cycle in the leaves at all understorey positions. The leaves more exposed to sunlight were larger with higher titratable acidity during the rainy season, while the leaves near the ground maintained the same rates of stomatal conductance and nocturnal acidification between seasons, with lowest values of carbon isotopes in the rainy season. Our research showed that some structural leaf traits (such as specific leaf mass, biomass, and saturated water content) are sensitive to variation in understorey position. In contrast, other physiological traits (stomatal conductance, transpiration, and fluorescence parameters) are more sensitive to seasonal variations. The results are a novelty in assessing the variation of CAM along the same plant in a height gradient and under field conditions.

Distinctive water bodies surrounding lakes: An effective indicator for drought monitoring and assessment

The response mechanisms of surface water to drought and the potential and performance of water body changes in drought monitoring and assessment remain insufficiently elucidated. We take the Poyang Lake Basin, which suffers from drastic water body changes and frequent droughts, as a representative. Through integrating multisource data to extract long-term precise water bodies, we construct standardized water body area/number anomaly indices (SAAI/SNAI). Subsequently, we quantify the correlation and time lag response between SAAI, SNAI and drought. Our findings reveal that overall, water body area and number in the Poyang Lake Basin all exhibit a significant correlation with typical drought indices. Among them, the large water body area has a higher correlation coefficient with drought, making it a more effective indicator for drought monitoring. Water body changes of Poyang Lake surrounding area offer a more precise reflection of drought conditions than other sub-basins and exhibit greater sensitivity to drought. Meanwhile, water body area changes in Poyang Lake surrounding area lag behind meteorological drought by approximately half a month. And the basin’s water body area can typically respond with changes to some prolonged and severe hydrological droughts about 1 to 2 months in advance. We propose an integrated mechanism for drought monitoring and assessment informed by these conclusions and use actual drought events for qualitative validation. The results indicate that it is possible to assess water body drought conditions for the next approximately half month based on current meteorological drought conditions. Also, combining water body area changes with meteorological drought severity can aid in evaluating hydrological drought conditions for the following about 1–2 months. We extend our investigation to explore the universality of these phenomenon across eight shallow lakes globally characterized by significant water fluctuations. The results reveal that the water body changes in most of these lakes exhibit good potential for drought monitoring and assessment, and present a strong consistency with deep soil moisture, allowing for the accurate reflection of deep soil drought conditions. The lag response patterns between water bodies and drought in Dongting Lake, Hongze Lake, and Tonlé Sap Lake—also situated in the monsoon climate zone—are more similar to those observed in Poyang Lake. These distinctive lake water bodies can serve as an innovative indicator for drought monitoring and assessment, providing potential support for endeavors in drought prevention and mitigation.

Differential modulation of photosystem II photochemical efficiency in six C4 xero-halophytes.

Xero-halophytes are the salt-tolerant plants of dry habitats that adapt efficient strategies to endure extreme salt and water fluctuations. This study elucidated the adaptations related to PSII photochemistry, photoprotection, and photoinhibition in six C4 xero-halophytes (Atriplex stocksii , Haloxylon stocksii , Salsola imbricata, Suaeda fruticosa, Desmostachya bipinnata , and Saccharum griffithii ) grown in their native habitats. Chlorophyll a fluorescence quenching measurements suggested that S. imbricata and H. stocksii maintained efficient PSII photochemistry by downregulating heat dissipation and keeping a high fraction of open PSII centres that indicates plastoquinone (PQ) pool oxidation. Fluorescence induction kinetics revealed that S. imbricata demonstrated the highest performance index of PSII excitation to the reduction of end electron acceptors. S. fruticosa sustained photochemical efficiency through enhanced dissipation of excess energy and a low fraction of open PSII centres, indicating PQ reduced state. The large light-harvesting antenna size, deduced from the chlorophyll a /b ratio in S. fruticosa apparently led to the superior performance index of PSII excitation to the reduction of intersystem electron carriers. A. stocksii retained more open PSII centres with responsive non-photochemical quenching to safely dissipate excess energy. Despite maintaining the highest pigment contents and stoichiometry, A. stocksii remained lowest in both performance indices. The grass species D. bipinnata and S. griffithii kept fewer PSII centres open during photoinhibition, as evidenced by downregulation of PSII operating efficiency. The results provide insights into the differential modulation of PSII photochemical efficiency through dynamic control of photoprotective energy dissipation, PQ pool redox states, and photoinhibitory shutdown in these xero-halophytes.

The importance of high total body water/fat free mass ratio and serial changes in body composition for predicting hospital mortality in patients with severe pneumonia: a prospective cohort study

PurposeThis study aimed to investigate the impact of body composition variables on hospital mortality compared to other predictive factors among patients with severe pneumonia. Additionally, we aimed to monitor the dynamic changes in body composition variables over the course on days 1, 3, and 8 after intensive care unit (ICU) admission for each patient.MethodsWe conducted a prospective study, enrolling patients with severe pneumonia admitted to the medical intensive care unit at Kaohsiung Chang Gung Memorial Hospital from February 2020 to April 2022. We collected clinical data from all patients and assessed their body composition at 1, 3, and 8 days post-ICU admission. On day 1, we analyzed clinical and body composition variables to predict in-hospital mortality.ResultsMultivariate analysis identified the Modified Nutrition Risk in the Critically Ill (mNUTRIC) score and the ratio of total body water to fat-free mass (TBW/FFM) as independent factors associated with in-hospital mortality in severe pneumonia patients. Receiver operating characteristic analysis determined that the TBW/FFM ratio was the most reliable predictive parameter of in-hospital mortality, with a cutoff value of 0.74. General linear regression with repeated measures analysis showed that hospital non-survivors displayed notable fluctuations in body water, fat, and muscle variables over the course of days 1, 3, and 8 after ICU admission.ConclusionsThe mNUTRIC score and TBW/FFM ratio emerged as independent factors for predicting hospital mortality, with the TBW/FFM ratio demonstrating the highest reliability as a predictive parameter.

Dynamics of land use and land cover change in the distal Okavango Delta, Botswana

ABSTRACT Population increase and socio-economic progress exert pressure on land use and land cover (LULC) in any geophysical environment. If not minimized, the pressure has the potential to unfold as unplanned and uncontrolled alterations in LULC. Remote sensing (RS) and geographical information systems (GIS) prove to be powerful tools for obtaining accurate and real-time information on the spatial distribution of land use and land cover change (LULCC) both spatially and temporally over a wide area. This research paper uses remotely sensed spatial data and a literature review to examine the extent of LULCC over three decades in the distal Okavango Delta with specific attention on Maun, Botswana. The study assesses changes in population growth, built-up areas, road/pavements, water fluctuations, hydrophytes and shrubs/trees dynamics from April 1990 to April 2020. Findings reveal that while the population of Maun increased from 26,768 to 85,293 between 1990–2020 built-up areas increased from 0.68 km2 to 9.61 km2 and shrubs/trees decreased from 13.53 km2 to 7.06 km2, respectively, within the same period. Grasslands increased from 8.57 km2 in 1990 to 13.44 km2 by 2020. The paper thus recommends the establishment of a two-kilometre-wide green belt around the settlement to stem any progressive encroachment into agricultural reserved land.

Effects of Surface Charge Distribution and Electrolyte Ions on the Nonlinear Spectra of Model Solid-Water Interfaces.

Molecular dynamics simulations of model charged solid/water interfaces were carried out to provide insight about the relationship between the second-order nonlinear susceptibility χ(2) and the structure of the interfacial water layer. The results of the calculations reveal that the density fluctuations of water extend to about 12 Å from the surface regardless of the system, while the orientational ordering of molecules is long-ranged and is sensitive to the presence of electrolytes. The charge localization on the surface was found to affect only the high-frequency part of the Im[χ(2)] spectrum, and the addition of salt has very little effect on the spectrum of the first water layer. For solid/neat water interfaces, the spectroscopically active part of the liquid phase has a thickness largely exceeding the region of density fluctuations, and this long-ranged nonlinear activity is mediated by the electric field of the molecules. The electrolyte ions and their hydration shells act in a destructive way on the molecular field. This effect, combined with the screening of the surface charge by ions, drastically reduces the thickness of the spectroscopic diffuse layer. There is an electrolyte concentration at which the nonlinear response of the diffuse layer is suppressed and the χ(2) spectrum of the interface essentially coincides with that of the first water layer.

Shallow water table rise and fluctuation between 1977 and 2010 in Madinah City, Saudi Arabia

Madinah City in Saudi Arabia is rapidly growing with high population growth, water demand, sewage generation, and agricultural activities. The hydrogeological layering sequence in Madinah City reveals that there are three main layers that extend within the areas between wadi systems. The shallow water table rise (SWTR) problem has risen in several areas of the city, and the fluctuations in the piezometric water observed from the shallow aquifer systems. The research aims to investigate the changes in shallow groundwater levels within the Madinah City. Sources of water table rise and fluctuations are investigated through an extensive field hydro-geological survey comprising wells drilling and water level monitoring, which indicated the following results between 1977 and 2010 including those of newly drilled wells: (i) water flow is partially blocked along wadi Alaqiq and this has caused an increased regional flow moving from west along wadi Alaqiq towards the central area; (ii) groundwater levels have changed in the agricultural areas as indicated by 15–26 m rise along wadi Alaqiq; (iii) groundwater level fluctuations as indicated by 590 m amsl (1977) against less than 575 m amsl (2010) in the east and southeast of the study area as a result of increased heavy pumping since past 37 years. The overall flow phenomenon is reflected in the groundwater gradients on an increasing trend with orientation from the western region along the wadi Alaqiq towards the central area and southeast which has invariably resulted in the overall declining of water levels throughout the affected area.

Composite water value: A way forward to balance the development and protection of transboundary lakes

Transboundary lakes are shared by multiple administrative regions. The key to balance the development and protection of transboundary lakes is to properly measure the value of water resources. Most of previous studies on the measurement of lake water resources value have not fully considered the ecosystem service function. This paper proposes a new concept “composite water value” to measure the value of transboundary lakes by integrating the external runoff value and the internal runoff value of water resources. The study constructs a composite water value measurement system for transboundary lakes, further analyzes its influencing factors,and applies the system to the case of Nansi Lake, a representative transboundary lake in eastern China. The results show that: (1) The composite water value of lakes is influenced by various factors, including industrial structure, water withdrawal, and water use methods, which impact the external runoff water value; meanwhile, the composite water quality and fluctuations in lake level are closely associated with the internal runoff water value. From 2008 to 2021, the average annual composite water value of Nansi Lake was 39.628 billion yuan, exhibiting a "rising-falling-fluctuating rising" trend due to pollution control policies, reduced precipitation, and enhanced water-saving technologies successively. (2) From a long-term perspective, it is necessary to focus on the internal runoff water use value of lakes. The internal runoff water value of Nansi Lake has been over 75% of the composite water value, and flood storage and water conservation are important manifestations of its ecosystem service value. (3) The external runoff water value of lake is closely related to the internal runoff water value, and relevant departments need to consider the balance between the water withdrawal of multiple cities along the lake and the retained water volume of the lake to achieve the maximum benefit of composite water value.

Nonlinear Effects of Hydrophobic Confinement on the Electronic Structure and Dielectric Response of Water.

Fundamental studies of the dielectrics of confined water are critical to understand the ion transport across biological and synthetic nanochannels. The relevance of these fundamental studies, however, surmounts the difficulty of probing water's dielectric constant as a function of a fine variation in confinement. In this work, we explore the computational efficiency of machine learning potentials to derive the confinement effects on the dielectric constant, polarization, and dipole moment of water. Our simulations predict an enhancement of the axial dielectric constant of water under extreme confinement, arising from either the formation of ferroelectric structures of ordered water or larger dipole fluctuations facilitated by the disruption of water's H-bond network. Our study highlights the impact of hydrophobic nanoconfinement on the dielectric constant and on the ionic and electronic structure of water molecules, pointing to the importance of geometric flexibility and electronic polarizability to properly model confinement effects on water.

High Spatial Resolution in Total Water Storage Variations Inferred From GPS: Case Study in the Great Lakes Watershed, US

AbstractAssessing spatiotemporal water storage variability in the Great Lakes Watershed (GLW) is critical given its transboundary status impacting both Canada and the United States. Here, we apply a novel inversion strategy to global positioning system (GPS) vertical movements to achieve high spatial resolution total water storage (TWS) variations in GLW through improved processing. The steps are composed of removing load changes driven by the lake water fluctuation by forward modeling, isolating the Great Lakes grids to solve the ill‐conditioned problem in inversion, and inverting the GPS residual series to estimate TWS variations on land (TWSGPS). The results show that the regional dense continuous GPS observation network can successfully resolve TWS on land at monthly timescales with 30–45 km spatial resolution. We also could effectively capture fine‐scale TWS features than GRACE/GFO mascon products. GRACE/GFO satellites largely underestimate seasonal and long‐term TWS spatial fluctuations, but their temporal patterns coincide with those from GPS. The average annual amplitude of TWSGPS on land reaches 82.0 mm, greatly exceeding estimates from GRACE/GFO (∼48.0 mm) and composite hydrological model outputs (∼62.0 mm). The seasonal groundwater fluctuations inferred from GPS have peak‐to‐peak amplitudes of ∼40 km3 with the maximum around September. This coincides with that from GRACE/GFO. However, the magnitudes and phases of groundwater storage from GPS vary markedly among the subbasins in GLW, and the different snow and soil moisture amounts measured in each subbasin cause discrepancies among these GPS estimates. This study shows the value of GPS data in spatially downscaling GRACE/GFO data and providing high‐resolution output at spatiotemporal scales with low latency.

Prędkość ultradźwiękowa analizy wpływu zawartości wody na kredę fosfatyczną

Water content may have a crucial effect on the petrophysical and mechanical properties of high porosity rocks such as chalk. Consequently, the water fluctuations may significantly influence the behaviour of engineering structures that are constructed in chalks. It is the aim of this study to illustrate how the elastic and strength properties of chalk can evolve considering water content variation using P-wave velocity and analytical analyses. To study the influence of water on the ultrasonic compressional wave velocity (VP), measurements of travel time of three samples subjected to different water content were performed. The Uniaxial Compressive Strength (UCS) in dry and saturated chalk specimens was also estimated. To clarify the possible influence of lithology on the physicomechanical properties of rocks, three samples of phosphatic chalk were studied in thin sections. Automated mineral analysis and textural imaging of the samples were performed using an FEI QEMSCAN®. The analyses of the Ultrasonic tests reveal that changes in the water content are associated with variations in the P-wave velocity. Based on P-wave velocity changes as a function of water content, analytical models have been used to predict the elastic and strength properties. The data indicate that the presence of water significantly reduced the elastic and strength parameters of the chalk, a result that is in agreement with the UCS laboratory tests. The derived equations can be used for predicting the elastic and strength properties of high-porous chalk from the P-wave velocity as a function of water content. This approach may avoid the necessity for time-consuming laboratory testing.

Hydrological response of the largest inland tectonic basin in Japan

The Itoigawa-Shizuoka tectonic line formed the largest inland tectonic basin in Japan. Taking advantage of the characteristics of the large tectonic basin, this study aims to clarify the hydrological response related to groundwater recharge and discharge in this area from field measurements such as monthly spring discharge measurements in the spring belt, infiltration measurements of irrigation recharge in rice paddy fields and analysis of stable isotopic ratios of oxygen and hydrogen. Volumetric water flow measurements in the tectonic basin demonstrate that the hydrological response function (HRF) is expressed as a linear equation. Despite the complex topography and geology of the mountain catchment and artificial recharge within the basin, this HRF is maintained, except for forced artificial irrigation in August when the natural water supply is significantly reduced, and except in March and April when snowmelt flows into the river. This study clarifies that monthly fluctuations in total groundwater flow within a basin can be estimated by applying HRF to monitoring data of total surface flow at the farthest downstream. The field measurements demonstrate that the rainfall in the mountain catchment area and artificial irrigation recharge in the basin greatly influence the fluctuation of groundwater flow rate, especially on the fluctuation of the spring water in the spring belt. Field data inferred that the frequent depletion of the springs in the inland tectonic basin, where all groundwater emerges at the most downstream, depends on the rapid decline in annual rainfall in mountain catchment areas. These observations suggest that the total groundwater resource in this region was affected not only by reduced irrigation recharge due to the historical paddy acreage reduction program implemented in Japan from 1971 to 2018, and by excessive groundwater extraction, but also by rapid decline in annual rainfall in mountain catchments that occurs non-periodically.

Physical Model Test of Deformation Self-Adaptive Mechanism of Landslide Mass

Reservoir impoundment induces a large amount of cumulative deformation of landslide body, leading to damage to the geological environment. Due to many yearly cycles of reservoir water fluctuation, the cumulative deformation of landslides tends to be stable, showing a self-adaptive deformation phenomenon. The study of the self-adaptive deformation mechanism is very important for evaluating landslide stability and achieving the safe operation of hydropower stations. To study the mechanism of self-adaptive deformation, two sets of physical models were used to monitor the groundwater, earth pressure, and cumulative deformation of landslide under periodic fluctuations of the reservoir water level. The results showed that the soil consolidation compaction, release of sliding stress, and increase in permeability are the three main factors of the self-adaptive deformation of landslide accumulation. The overall permeability decreased first and then increased, the front permeability increased greatly, and the middle and rear permeability decreased. The main factors that affected the permeability change were deformation and seepage force.

Assessment of seasonal fluctuation in heavy metal contamination in sediments and surface water of Narmada River, India

ABSTRACT This study aimed to assess the seasonal fluctuation of heavy metal contamination in the sediments and surface water of the Narmada River. In this context, samples were gathered from six stations along the river in 2021–2022 and their concentrations were determined by utilizing Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The results in sediments, the average concentrations of As, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were 0.05, 1.03, 2.47, 1.64, 750.17, 17.75, 0.54, 0.13, and 1.12 mg/kg and in water, the average concentrations of Co, Fe, Ni, and Zn were 0.03 μg/l, 0.01 mg/l, 0.08 μg/l, and 0.39 μg/l. Seasonal fluctuation in sediments revealed that concentration of metals As, Cu, Fe, Ni, and Zn peaked during the rainy climate, while Co and Cr peaked during the post-monsoon and Mn and Pb peaked during the summer climate. Seasonal fluctuation in water, Co, Ni, and Zn exhibits their highest concentrations during the post-monsoon. The finding of pollution indices revealed that the contamination level was low to moderate. Cluster analysis revealed anthropogenic and agricultural runoff water as a contributor to contamination. The findings of this research enhance comprehension of heavy metal contamination in sediment and water of the Narmada River.

Ab Initio Characterization of the CO2-Water Interface Using Unsupervised Machine Learning for Dimensionality Reduction.

Precise characterization of the supercritical CO2-water interface under high pressure and temperature conditions is crucial for the geological storage of carbon dioxide (CO2) in deep saline aquifers. Molecular dynamics (MD) simulations offer a valuable approach to gaining insight into the CO2-water interface at a microscopic level. However, no attempt has been made to characterize the CO2-water interface with the accuracy afforded by ab initio calculations. In this study, we performed ab initio MD (AIMD) simulations to investigate the structural and dynamical properties of the CO2-water interface, comparing the results with those obtained from classical force-field MD (FF-MD) simulations. Molecular orientation at the interface was well reproduced in both AIMD and FF-MD simulations. Characteristic structural fluctuations of water at the interface were unveiled by applying multidimensional scaling and time-dependent principal component analysis to the AIMD trajectories; however, they were not prominent in the FF-MD simulations. Furthermore, our study demonstrated a marked difference in the residence time of molecules in the interface region between AIMD and FF-MD simulations, indicating that time-dependent properties of the CO2-water interface strongly depend on the description of the intermolecular forces.

Multi-decadal floodplain classification and trend analysis in the Upper Columbia River valley, British Columbia

Abstract. Floodplain wetland ecosystems experience significant seasonal water fluctuation over the year, resulting in a dynamic hydroperiod, with a range of vegetation community responses. This paper assesses trends and changes in land cover and hydroclimatological variables, including air temperature, river discharge, and water level in the Upper Columbia River Wetlands (UCRW), British Columbia, Canada. A land cover classification time series from 1984 to 2022 was generated from the Landsat image archive using a random forest algorithm. Peak river flow timing, duration, and anomalies were examined to evaluate temporal coincidence with observed land cover trends. The land cover classifier used to segment changes in wetland area and open water performed well (kappa of 0.82). Over the last 4 decades, observed river discharge and air temperature have increased, precipitation has decreased, the timing of peak flow is earlier, and the flow duration has been reduced. The frequency of both high-discharge events and dry years have increased, indicating a shift towards more extreme floodplain flow behavior. These hydrometeorological changes are associated with a shift in the timing of snowmelt, from April to mid-May, and with seasonal changes in the vegetative communities over the 39-year period. Thus, woody shrubs (+6 % to +12 %) have expanded as they gradually replaced marsh and wet-meadow land covers with a reduction in open-water area. This suggests that increasing temperatures have already impacted the regional hydrology, wetland hydroperiod, and floodplain land cover in the Upper Columbia River valley. Overall, there is substantial variation in seasonal and annual land cover, reflecting the dynamic nature of floodplain wetlands, but the results show that the wetlands are drying out with increasing areas of woody/shrub habitat and loss of aquatic habitat. The results suggest that floodplain wetlands, particularly marsh and open-water habitats, are vulnerable to climatic and hydrological changes that could further reduce their areal extent in the future.

Osmosensor-mediated control of Ca2+ spiking in pollen germination

Higher plants survive terrestrial water deficiency and fluctuation by arresting cellular activities (dehydration) and resuscitating processes (rehydration). However, how plants monitor water availability during rehydration is unknown. Although increases in hypo-osmolarity-induced cytosolic Ca2+ concentration (HOSCA) have long been postulated to be the mechanism for sensing hypo-osmolarity in rehydration1,2, the molecular basis remains unknown. Because osmolarity triggers membrane tension and the osmosensing specificity of osmosensing channels can only be determined in vivo3–5, these channels have been classified as a subtype of mechanosensors. Here we identify bona fide cell surface hypo-osmosensors in Arabidopsis and find that pollen Ca2+ spiking is controlled directly by water through these hypo-osmosensors—that is, Ca2+ spiking is the second messenger for water status. We developed a functional expression screen in Escherichia coli for hypo-osmosensitive channels and identified OSCA2.1, a member of the hyperosmolarity-gated calcium-permeable channel (OSCA) family of proteins6. We screened single and high-order OSCA mutants, and observed that the osca2.1/osca2.2 double-knockout mutant was impaired in pollen germination and HOSCA. OSCA2.1 and OSCA2.2 function as hypo-osmosensitive Ca2+-permeable channels in planta and in HEK293 cells. Decreasing osmolarity of the medium enhanced pollen Ca2+ oscillations, which were mediated by OSCA2.1 and OSCA2.2 and required for germination. OSCA2.1 and OSCA2.2 convert extracellular water status into Ca2+ spiking in pollen and may serve as essential hypo-osmosensors for tracking rehydration in plants.

Acclimation to higher temperature and antioxidant supplemented diets improved rainbow trout (Oncorhynchus mykiss) resilience to heatwaves

Coldwater species are challenged with increasing water temperatures and fluctuations over their upper thermal limits. This study evaluated the potential of acclimation to higher temperature and dietary antioxidants capacity to mitigate the adverse effects of heat shocks in rainbow trout. To this end, rainbow trout fingerlings were acclimated at optimal (14 °C) and high (20 °C) temperatures and fed on selenium (5 mg/kg) and polyphenol (2 g/kg) supplemented diets for 60 days and then were exposed to heat shocks by increasing water temperature up to 30 °C. Growth performance, survival rate, haemato-immunological parameters, and expression of HSP70α, HSP70β, HSP90β, and IL-1β genes were measured to evaluate the hypothesises. The rainbow trout acclimated to 20 °C and fed on antioxidants supplemented diets showed a significantly higher aftershock survival rate. Moreover, fish acclimated to higher temperature showed higher red blood cell counts as well as serum total protein and albumin during the acclimation trial and heat shocks phase. Acclimation to higher temperature and feeding on antioxidants remarkably enhanced fish immune and antioxidant capacity in comparison to fish adapted to cold water and fed on the basal diet measured by improved respiratory burst and lysozyme activities and upregulation of IL-1β expression during exposure of fish to heat shocks. Furthermore, fish acclimated to higher temperature, especially those fed on antioxidant supplemented diets, showed lower expression levels of HSPs genes during the heat shock phase, indicating that high heat shocks were less stressful for these fish in comparison to cold water acclimated fish. This finding was also supported by lower cortisol levels during heat shocks in fish acclimated to higher temperature. In conclusion, the results of this study indicated that acclimation to higher temperature and/or fed on diets supplemented by selenium and polyphenol, can help to mitigate the adverse effects of the heat shock in rainbow trout.