Salt Damage Research Articles

Identification of salt tolerance of different Chinese kale cultivars under NaCl stress at seedling stage

In order to understand the salt tolerance of different Chinese kale varieties at seedling stage and screen out the varieties with strong salt tolerance at seedling stage, the seeds of 26 Chinese kale varieties were used as materials. The growth indexes, physiological indexes, seedling rate and salt damage index of different Chinese kale varieties were compared and cluster analyzed by means of tissue culture. The results showed that: (1) under 160 mmol∙L−1 NaCl stress, the different Chinese kale varieties at growth indexes, physiological indexes, seedling rate and salt damage index were significantly different, the relative seedling rate of R4, R14 and R32 reached 100.00%, and the salt damage index was the lowest, which was 20.00%; The correlation analysis showed that the relative seedling rate, the relative content of soluble protein, the relative content of soluble sugar and the relative value of Leaf SPAD were all negatively correlated with the salt damage index, and the relative conductivity and the relative content of malondialdehyde were all positively correlated with the salt damage index. (2) The average value of 14 salt tolerance indexes was used to cluster analyze the salt tolerance of 26 Chinese kale varieties. The tested materials were divided into four categories: high salt tolerance, moderate salt tolerance, low salt tolerance and salt sensitivity. R14, R25, R30 and R32 were highly salt tolerant varieties and R24 was salt sensitive varieties, which laid a foundation for further breeding and genetic research of salt tolerant varieties.

MdWRKY71 as a positive regulator involved in 5-aminolevulinic acid-induced salt tolerance in apple

5-Aminolevulinic acid (ALA), is a novel plant growth regulator that can enhance plant tolerance against salt stress. However, the molecular mechanism of ALA is not well studied. In this study, ALA improved salt tolerance of apple (Malus × domestica 'Gala') when the detached leaves or cultured calli were used as the materials. The expression of MdWRKY71, a WRKY transcription factor (TF) gene was found to be responsive to NaCl as well as ALA treatment. Functional analysis showed that overexpressing (OE)-MdWRKY71 significantly improved the salt tolerance of the transgenic apple, while RNA interfering (RNAi)-MdWRKY71 reduced the salt tolerance. However, exogenous ALA alleviated the salt damage in the RNAi-MdWRKY71 apple. When MdWRKY71 was transferred into tobacco, the salt tolerance of transgenic plants was enhanced, which was further improved by exogenous ALA. Subsequently, MdWRKY71 bound to the W-box of promoters of MdSOS2, MdNHX1, MdCLC-g, MdSOD1, MdCAT1 and MdAPX1, transcriptionally activating the gene expressions. Since the genes are responsible for Na+ and Cl− transport and antioxidant enzyme activity respectively, it can be concluded that MdWRKY71, a new TF, is involved in ALA-improved salt tolerance by regulating ion homeostasis and redox homeostasis. These results provided new insights into the transcriptional regulatory mechanism of ALA in enhancing apple salt tolerance.

Research on Experimental Hypertension in Prague (1966-2009).

The study of ontogenetic aspects of water and electrolyte metabolism performed in the Institute of Physiology (Czechoslovak Academy of Sciences) led to the research on the increased susceptibility of immature rats to salt-dependent forms of hypertension since 1966. Hemodynamic studies in developing rats paved the way to the evaluation of hemodynamic mechanisms during the development of genetic hypertension in SHR. A particular attention was focused on altered renal function and kidney damage in both salt and genetic hypertension with a special respect to renin-angiotensin system. Renal damage associated with hypertension progression was in the center of interest of several research groups in Prague. The alterations in ion transport, cell calcium handling and membrane structure as well as their relationship to abnormal lipid metabolism were studied in a close cooperation with laboratories in Munich, Glasgow, Montreal and Paris. The role of NO and oxidative stress in various forms of hypertension was a subject of a joint research with our Slovak colleagues focused mainly on NO-deficient hypertension elicited by chronic L-NAME administration. Finally, we adopted a method enabling us to evaluate the balance of vasoconstrictor and vasodilator mechanisms in BP maintenance. Using this method we demonstrated sympathetic hyperactivity and relative NO deficiency in rats with either salt-dependent or genetic hypertension. At the end of the first decennium of this century we were ready to modify our traditional approach towards modern trends in the research of experimental hypertension. Keywords: Salt-dependent hypertension o Genetic hypertension o Body fluids o Hemodynamics o Ion transport o Cell membrane structure and function o Renal function o Renin-angiotensin systems.

Physiological Responses and Salt Tolerance Evaluation of Different Varieties of Bougainvillea under Salt Stress.

Soil salinization significantly impacts the ecological environment and agricultural production, posing a threat to plant growth. Currently, there are over 400 varieties of Bougainvillea with horticultural value internationally. However, research on the differences in salt tolerance among Bougainvillea varieties is still insufficient. Therefore, this study aims to investigate the physiological responses and tolerance differences of various Bougainvillea varieties under different concentrations of salt stress, reveal the effects of salt stress on their growth and physiology, and study the adaptation mechanisms of these varieties related to salt stress. The experimental materials consisted of five varieties of Bougainvillea. Based on the actual salinity concentrations in natural saline-alkali soils, we used a pot-controlled salt method for the experiment, with four treatment concentrations set: 0.0% (w/v) (CK), 0.2% (w/v), 0.4% (w/v), and 0.6% (w/v). After the Bougainvillea plants grew stably, salt stress was applied and the growth, physiology, and salt tolerance of the one-year-old plants were systematically measured and assessed. The key findings were as follows: Salt stress inhibited the growth and biomass of the five varieties of Bougainvillea; the 'Dayezi' variety showed severe salt damage, while the 'Shuihong' variety exhibited minimal response. As the salt concentration and duration of salt stress increase, the trends of the changes in antioxidant enzyme activity and osmotic regulation systems in the leaves of the five Bougainvillea species differ. Membrane permeability and the production of membrane oxidative products showed an upward trend with stress severity. The salt tolerance of the five varieties of Bougainvillea was comprehensively evaluated through principal component analysis. It was found that the 'Shuihong' variety exhibited the highest salt tolerance, followed by the 'Lvyehuanghua', 'Xiaoyezi', 'Tazi', and 'Dayezi' varieties. Therefore, Bougainvillea 'Shuihong', 'Lvyehuanghua', and 'Xiaoyezi' are recommended for extensive cultivation in saline-alkali areas. The investigation focuses primarily on how Bougainvillea varieties respond to salt stress from the perspectives of growth and physiological levels. Future research could explore the molecular mechanisms behind the responses to and tolerance of different Bougainvillea varieties as to salt stress, providing a more comprehensive understanding and basis for practical applications.

SOS1 gene family in mangrove (Kandelia obovata): Genome-wide identification, characterization, and expression analyses under salt and copper stress

BackgroundSalt Overly Sensitive 1 (SOS1), a plasma membrane Na+/H+ exchanger, is essential for plant salt tolerance. Salt damage is a significant abiotic stress that impacts plant species globally. All living organisms require copper (Cu), a necessary micronutrient and a protein cofactor for many biological and physiological processes. High Cu concentrations, however, may result in pollution that inhibits the growth and development of plants. The function and production of mangrove ecosystems are significantly impacted by rising salinity and copper contamination.ResultsA genome-wide analysis and bioinformatics techniques were used in this study to identify 20 SOS1 genes in the genome of Kandelia obovata. Most of the SOS1 genes were found on the plasma membrane and dispersed over 11 of the 18 chromosomes. Based on phylogenetic analysis, KoSOS1s can be categorized into four groups, similar to Solanum tuberosum. Kandelia obovata's SOS1 gene family expanded due to tandem and segmental duplication. These SOS1 homologs shared similar protein structures, according to the results of the conserved motif analysis. The coding regions of 20 KoSOS1 genes consist of amino acids ranging from 466 to 1221, while the exons include amino acids ranging from 3 to 23. In addition, we found that the 2.0 kb upstream promoter region of the KoSOS1s gene contains several cis-elements associated with phytohormones and stress responses. According to the expression experiments, seven randomly chosen genes experienced up- and down-regulation of their expression levels in response to copper (CuCl2) and salt stressors.ConclusionsFor the first time, this work systematically identified SOS1 genes in Kandelia obovata. Our investigations also encompassed physicochemical properties, evolution, and expression patterns, thereby furnishing a theoretical framework for subsequent research endeavours aimed at functionally characterizing the Kandelia obovata SOS1 genes throughout the life cycle of plants.

Insight into the salt damage mechanism to the asphalt-aggregate interface in recycled asphalt mixtures at different salt environments using molecular dynamics and DFT simulations

In coastal areas, the complex salt environment poses new challenges to the interfacial stability and service durability of hot recycled asphalt pavements. To investigate the influence mechanism of salt environment on the adhesion properties of asphalt-aggregate interface, this study employed molecular dynamics (MD) simulation and density functional theory (DFT) to analyze the interfacial interaction energy, molecular diffusion behavior, component distribution, and molecular electrostatic property at asphalt-aggregate interface. The results show that as the content of aged asphalt increased, the interaction between asphalt and anions (Cl⁻ and SO₄²⁻) is weaker than that with cations (Na⁺, Mg²⁺ and Ca²⁺). H₂O causes the aromatics, saturates and resins to move away from the interface. Cl⁻ causes the saturates to further move away from the interface, while Na⁺ and Mg²⁺ bring the aromatics closer to the interface. Due to the greater polarity of SO₄²⁻, it moves the resins closer to the interface. With increasing aged asphalt content, the number of hydrogen bonds between asphalt and SiO₂ increases from none to some, thus enhancing the interfacial adhesion. However, this adhesion becomes more susceptible to salts. The aging effect redistributes the charge of asphalt molecules, concentrating negative potentials on the carbonyl and sulfoxide functional groups located on the outside of molecules. This increases the polarity of the asphalt molecules, making them more susceptible to salt ion attack. These findings contribute to the understanding of the adhesion properties of recycled asphalt mixtures in extreme salt environments.

The spectral inversion model for electrical conductivity in mural plaster following phosphate erosion based on fractional order differentiation and novel spectral indices

The Dunhuang murals are a precious treasure of China’s cultural heritage, yet they have long been affected by salt damage. Traditional methods for detecting salt content are costly, inefficient, and may cause physical harm to the murals. Among current techniques for measuring salt content in murals, hyperspectral remote sensing technology offers a non-invasive, circumventing issues of high costs, low efficiency. Building on this, the study constructs an inversion model for the Electrical Conductivity (EC) values of mural plaster subjected to phosphate erosion, through the integration of Fractional Order Differentiation (FOD), a novel three-band spectral index, and the Partial Least Squares Regression algorithm. The specific research contents include: (1) Initially, in preparation for the experiments, the materials used to create the samples underwent a rigorous desalting process, and phosphate solutions were prepared using deionized water to ensure uniform experimental conditions and the accuracy of the results. These meticulous preprocessing steps guaranteed that the measured EC values exhibited a clear correlation with the phosphate content. Subsequently, by employing qualitative experimental analysis techniques, this study was able to more accurately simulate the real-world scenarios of mural plaster affected by salt damage, enabling a deeper investigation into the mechanisms by which salts inflict microscopic damage to murals. (2) Explores the absorption mechanisms and characteristic spectral bands of the Electrical Conductivity (EC) values measured after the phosphate erosion of mural plaster. By integrating the optimal spectral indices, a univariate linear regression model is constructed, providing a basis for the rapid quantitative measurement of electrical conductivity in murals. (3) By comparing the accuracy of the Phosphate Simple Ratio (PSR) and Phosphate Normalized Difference Index (PNDI) spectral indices based on the linear regression model, the first six orders of the highest accuracy spectral index were selected as the optimal three-band spectral index combination, used as explanatory variables, with mural plaster electrical conductivity as the response variable, employing the PLSR method to construct the mural phosphate content high-spectral feature inversion model. The study’s findings include: (1) Surfaces of samples deteriorated by phosphate erosion formed numerous irregularly shaped crystal clusters, exhibiting uneven characteristics. (2) By comparing the outcomes of different orders of fractional differentiation, it was found that the model performance reached its optimum at a 0.3 order of differentiation for both PSR and PNDI data, with a determination coefficient (Q2) of 0.728. (3) Utilizing PLSR, this study employed the previously determined optimal six-order three-band spectral index combination as explanatory variables, with salt content as the response variable, successfully constructing the high-spectral feature inversion model for mural electrical conductivity with a determination coefficient (Q2) of 0.815. This provides an effective technical means for monitoring the salt damage conditions of precious cultural heritage such as murals.

A model for inversion of hyperspectral characteristics of phosphate content in mural plaster based on fractional-order differential algorithm

The Dunhuang murals, a significant part of Chinese heritage, have suffered deterioration primarily due to environmental and chemical factors, notably salt damage. This study proposes a sophisticated method that synergizes Fractional Order Differentiation (FOD) and Partial Least Squares Regression (PLSR) to accurately invert the phosphate content in the mural plaster of the Dunhuang paintings. The focal points of the research include: (1) To address the issue of information loss and reduced modeling precision caused by integer-order differentiation algorithms, the FOD method is employed for preprocessing spectral data. This approach ensures the fine spectral differences in the phosphate content of the mural plaster are precisely captured, (2) Utilizing PLSR, the study models the spectral bands identified at a significance level of 0.01 with measured conductivity values, thereby enabling the precise prediction of the phosphate content in the murals. The research outcomes reveal: (1) The FOD method can elucidate the nonlinear characteristics and variation patterns of the mural samples in the spectral data. As the order increases from zero to two, the number of spectral bands meeting the 0.01 significance test initially decreases and then increases. The highest absolute value of the positive correlation coefficient is observed at the 1.9 order, corresponding to the 2077 nm band, (2) For predicting the phosphate content in the murals, the model at the 1.9 order is most suitable for inversion. This model, after cross-validation, achieves a maximum R2 value of 0.861. This study created an efficient FOD-based model for estimating phosphate in mural plaster.

Encapsulated crystallisation inhibitor as a long-term solution to mitigate salt damage in hydraulic mortars

Salt (NaCl) weathering in mortar, can be mitigated by incorporating a crystallisation inhibitor (sodium ferrocyanide) during mortar preparation. However, the service-life of the inhibitor is limited, due to its susceptibility to leaching out of mortar. Encapsulating the inhibitor in chitosan-calcium alginate capsules has demonstrated controlled-release of the inhibitor and therefore, reduction in its leaching. Nevertheless, the addition of capsules may have a negative effect on mortar's properties and/or its salt-weathering resistance. In this research, natural hydraulic lime (NHL) and commercial cement-based mortars were prepared, with encapsulated inhibitor and with directly mixed-in inhibitor. Mechanical and physical properties of mortars were assessed experimentally. An accelerated NaCl-weathering test was performed to assess the durability of mortar to salt damage. The damage evolution was assessed visually and by quantifying material loss, efflorescence and leaching of the inhibitor. At the end of the test, crystal morphology inside the pores was examined using SEM. The results show that adding inhibitor, both in encapsulated and mixed-in form, had a negligible effect on the properties of NHL and cement-based mortars. Compared to the reference mortar without inhibitor, NHL-mortars with mixed-in inhibitor and encapsulated inhibitor had a better durability to salt damage, showing negligible material loss. The capsules facilitated controlled-release and reduced leaching of the inhibitor. In cement-based mortars including the reference, no damage was observed; still, the inhibitor was shown to be effective in modifying the salt crystal habit. The results show that encapsulation of the inhibitor can improve the service-life of the mortar without compromising its performance.

Effects of Saline–Alkali Composite Stress on the Growth and Soil Fixation Capacity of Four Herbaceous Plants

Plants play a crucial role in soil fixation and enhancement of slope stability, and saline–alkaline stress is one of the main restrictions inhibiting plant growth and development. At present, there is a lack of research on the effects of saline–alkaline composite stress on the mechanical properties of the root system and the erosion resistance of the root–soil complex. In this study, three gradients of saline–alkaline composite stress treatments and a control of saline-free treatment was set up for Oenothera biennis, Perilla frutescens, Echinops sphaerocephalus, and Lychnis fulgens. The plant salt damage rate, osmotic index, antioxidant enzyme activity and plant root morphological indicators were measured. The biomechanical characteristics were determined by stretching tests, the resistance of the plant was measured by a whole-plant vertical uprooting test, and the anti-erosion capacity of the root soil composite was measured by scrubbing test. The results showed that, at 200 mM, the salt damage index and salt damage rate of the four plants, in descending order, were as follows: E. sphaerocephalus < L. fulgens < O. biennis < P. frutescens. Among them, SOD of Perilla frutescens did not play an obvious protective role, and the substantial changes in CAT and POD, as well as the content of soluble sugars, soluble proteins, and proline, showed its sensitivity to saline and alkaline stresses. Root growth was also significantly suppressed in all four plants, the 100- and 200-mM concentrations of saline solution significantly reduced the average tensile strength of O. biennis and P. frutescens, while the saline–alkali solution of 200 mM significantly reduced the elongation of E. sphaerocephalus and L. fulgens, and significantly elevated the soil detachment rate of the root–soil composite for E. sphaerocephalus. Additionally, all three concentrations of saline treatments significantly reduced the pullout resistance of all 4 plants. There was a negative power rate relationship between tensile resistance and root diameter in four plant species, while the relationship between tensile strength and root diameter showed a negative power law only for L. fulgens treated with 0–50 mM saline solution. There was no significant correlation between elongation and root diameter in the four plants. P. frutescens had the greatest tensile resistance and strength, as well as the lowest rate of elongation, while L. fulgens possessed the greatest pullout resistance, and both had comparable resistance to erosion of the root–soil complex. Therefore, compared to the other three plants, L. fulgens is more suitable for soil reinforcement applications on saline slopes.

Capsule controlled release of crystallisation inhibitors in mortars

Crystallisation inhibitors, such as sodium ferrocyanide (NaFeCN), are highly effective in mitigating NaCl-induced weathering in lime-based mortars; however, direct addition of NaFeCN in lime-mortars increases its susceptibility to leaching and rapid depletion, thus compromising long-term performance. Here, we present hydrogel-capsules for the controlled-release of NaFeCN within hydraulic mortars for the prolonged prevention of salt weathering. Capsules were prepared by complexing chitosan and calcium-alginate in different ratios containing different concentrations of NaFeCN. The release of NaFeCN from these capsules was measured in (1) simulated lime-mortar solution (2) from mortar specimens incorporated with calcium alginate (CA) and chitosan-calcium-alginate (Cs-CA) capsules using ultraviolet–visible light spectrophotometry and Inductive Coupled Plasma-Optical Emission Spectroscopy. Mortars containing Cs-CA capsules exhibited controlled-release of NaFeCN with four times lower effective diffusion coefficient, compared to incorporating NaFeCN directly in mortar. Conversely, mortar containing CA capsules (without chitosan) released NaFeCN rapidly. Thus, chitosan’s presence in CA is necessary for tuning NaFeCN release and the reason may be attributed to chitosan’s role in reducing CA’s permeability and chitosan’s electrostatic-attraction to ferrocyanide anions, slowing diffusion of the latter. In conclusion, using Cs-CA capsules can control the release of NaFeCN within mortar, providing a steady NaFeCN supply to prolong mortar’s resistance against salt damage.

Application Model of Hyperspectral Technology Based on Novel Spectral Indices for Salinity Assessment in Soil Heritage Sites

Abstract. The Dunhuang murals are a precious treasure of China's cultural heritage, yet they have long been affected by salt damage. Traditional methods for detecting salt content are costly, inefficient, and may cause physical harm to the murals. Among current techniques for measuring salt content in murals, hyperspectral remote sensing technology offers a non-invasive , circumventing issues of high costs, low efficiency. Building on this, our study developed a high-spectral feature inversion model for mural phosphate content using Fractional Order Differentiation (FOD), a novel three-band spectral index, and Partial Least Squares Regression (PLSR) algorithm. The specific research contents include: 1) Exploring the absorption mechanism of phosphates and their characteristic bands, combined with the optimal spectral index to construct a univariate linear regression model, providing a basis for rapid quantitative measurement of mural phosphate content. 2) By comparing the accuracy of the PSR and PNDI spectral indices based on the linear regression model, the first six orders of the highest accuracy spectral index were selected as the optimal three-band spectral index combination, used as explanatory variables, with mural plaster electrical conductivity as the response variable, employing the PLSR method to construct the mural phosphate content high-spectral feature inversion model. The study's findings include: 1) By comparing the outcomes of different orders of fractional differentiation, it was found that the model performance reached its optimum at a 0.3 order of differentiation for both PSR and PNDI data, with a determination coefficient (R2) of 0.728. 2) Utilizing PLSR, this study employed the previously determined optimal six-order three-band spectral index combination as explanatory variables, with salt content as the response variable, successfully constructing the high-spectral feature inversion model for mural phosphate content with a determination coefficient (R2) of 0.815. This provides an effective technical means for monitoring the salt damage conditions of precious cultural heritage such as murals.

A Novel Hyperspectral Salt Assessment Model for Weathering in Architectural Ruins

Abstract. The Dunhuang murals, a significant part of Chinese heritage, have suffered deterioration primarily due to environmental and chemical factors, notably salt damage. This study proposes a sophisticated method that synergizes Fractional Order Differentiation (FOD) and Partial Least Squares Regression (PLSR) to accurately invert the phosphate content in the Mural Plaster of the Dunhuang paintings. The focal points of the research include: 1) To address the issue of information loss and reduced modeling precision caused by integer order differentiation algorithms, the FOD method is employed for preprocessing hyperspectral data. This approach ensures the fine spectral differences in the phosphate content of the Mural Plaster are precisely captured, 2) Utilizing PLSR, the study models the spectral bands identified at a significance level of 0.01 with measured conductivity values, thereby enabling the precise prediction of the phosphate content in the murals. The research outcomes reveal: 1) The FOD method can elucidate the nonlinear characteristics and variation patterns of the mural samples in the hyperspectral curve.As the order increases from zero to two, the number of spectral bands meeting the 0.01 significance test initially decreases and then increases. The highest absolute value of the positive correlation coefficient is observed at 1.9 orders, corresponding to the 2077 nm band, 2) For predicting the phosphate content in the murals, the model at 1.9 orders is most suitable for inversion. This model, after cross-validation, achieves a maximum R2 value of 0.783. This study created an efficient FOD-based model for estimating phosphate in mural plasters.

Dynamic modeling of the moisture and salt's transport in the unearthed terracotta warriors of emperor Qin's mausoleum museum, China

Terracotta figurines excavated from archaeological sites frequently exhibit salt damage due to moisture-salt transport. Understanding this dynamic within the terracotta figurines and soil system is essential for accurately predicting salt damage and implementing well-informed, timely preventative measures. While moisture-salt transport in the soils of historical sites is well-documented, the numerical modeling of this process is rare, specifically within the Terracotta figurines-soil coupled system. In the present work, a numerical model focused on the Terracotta figurine-soil system at Emperor Qin's Mausoleum Museum (China) was established, which employed the variable saturation Richards flow equation and the Fickian advection-diffusion equation. The model was validated using soil column experiments. The results showed that the semi-buried figurines were more susceptible to salt damage, with uneven salt distribution primarily due to moisture-salt transport at the interface. After the excavation, the first month was identified as a critical period for rapid migration of moisture and salt, representing the highest risk of damage. These insights offer a framework for estimating the risk of salt damage over time, underpinning the development of future abatement strategies. This study not only advances the understanding of salt damage in Terracotta figurines but also lays the groundwork for safeguarding these archaeological treasures.

Identification and Evaluation of Celery Germplasm Resources for Salt Tolerance

This study evaluated the salt tolerance in 40 celery germplasm resources to clarify the different salt tolerances of celery germplasm. A gradient treatment with different concentrations of NaCl solutions (100, 200, and 300 mmol·L−1) was used to simulate salt stress. After 15 days of salt treatment, 14 indicators related to plant growth, physiology, and biochemistry were determined. The results showed that different celery varieties responded differently to salt stress. Notably, there were significant variations in below-ground dry weight, root–crown ratio, antioxidant enzyme activity, and soluble protein content among the accessions under salt stress. Principal component analysis was used to identify important indices for evaluating salt tolerance, including plant height, spread, content of soluble protein, and so on. A comprehensive evaluation was conducted utilizing the salt damage index, principal component analysis, affiliation function analysis, and cluster analysis. The 40 celery germplasms were classified into five highly salt-tolerant, seven salt-tolerant, fifteen moderately salt-tolerant, nine salt-sensitive, and four highly salt-sensitive germplasms. SHHXQ, MXKQ, XBQC, XQ, and TGCXBQ were highly salt-tolerant germplasms, and BFMSGQ, HNXQ, ZQ, and MGXQW were highly salt-sensitive germplasms. The results of this study provide a reference for the variety of celery cultivation in saline areas and lay a foundation for the selection and breeding of salt-tolerant varieties of celery.

Laboratory exploration of a novel method to protect silicate relics against salt efflorescence by directional induction of water

Salt efflorescence is one of the critical problems for the preservation of immovable silicate relics. Salt efflorescence mainly comes from continuous cycles of crystallization/dissolution or hydration/dehydration of salts in confined pores in silicate relics. Many protocols have been developed in attempts to alleviate possible salt damages with minor success because of endless water and salt feed from underground. In this study, we propose and design a novel technique for salt damage prevention and protection of immovable relics. Materials with higher water-absorbing ability than matrix are applied to control the water and salt migration direction in simulated sand samples. The distribution of moisture content on the surface of sand is followed by hyperspectral imaging. It appears that water and salt molecules will preferentially transport towards positions containing higher water-absorbing material. Both organic and inorganic high water-absorbing materials show effective in controlling the water and salt migration direction, which provides a new approach for the prevention and protection of salt efflorescence in silicate cultural relics.

Quantitative analysis on the impact factors of salt weathering for sandstone grottoes along Silk Road, China

A large number of exquisite sandstone grottoes remaining along the Silk Road in Northwest China suffer from severe salt damage due to the vulnerability of the sandstone materials used and long-term continuous fluctuation of environmental conditions. Exploring the mechanism of salt weathering is crucial for the conservation of these grottoes. This study aims to quantitatively analyze the damage potential and the main impact factors of salt weathering in 14 grottoes along the Silk Road that were selected and investigated by using visual evaluation, salt analysis including thermodynamic modeling, and a comprehensive evaluation based on the entropy weight method. The results indicate that salt weathering of the sandstone grottoes is primarily characterized by efflorescences, peeling, and powdering. The overall salt content within the weathering layer typically exceeds a threshold of 1 %. Within the semi-arid area, the humidity fluctuations critical for significant volume changes in crystalline salts fall within the ranges 46–76 % and 16–30 %. In the semi-humid area, these ranges are 58–90 %, 42–50 %, and 16–30 %. A total of 14 salts can precipitate in the study area with NaCl, NaNO3, KNO3, Na2SO4·xH2O and several double salts occuring most frequently. Generally, the damage degree of sandstones grottoes in the semi-humid area is more serious than that in the semi-arid area. Through a comparison of visual inspection and more comprehensive quantitative evaluation, it has been confirmed that the salt damage is primarily influenced by the factors salt content, salt type, and environmental conditions. Furthermore, the order of influence for each factor on salt weathering can be ranked as follows: salt content > salt type > environmental conditions. This study quantitatively reveals the impact of various factors on salt weathering and proposes a method to evaluate the salt damage potential, which is of great significance for the preventive conservation of sandstone grottoes.

Morphological and Physiological Responses of Two Penstemon Species to Saline Water Irrigation

Penstemon, with more than 250 species native to North America, holds significant aesthetic and ecological value in Utah, supporting diverse pollinators. Despite their significance, the survival of penstemon is threatened by challenges such as habitat loss, climate change, and Utah’s naturally high soil salinity. To address these challenges and understand their adaptability, this study evaluated the salt tolerance of two penstemon species [Penstemon davidsonii (Davidson’s penstemon) and Penstemon heterophyllus (foothill penstemon)] under controlled greenhouse conditions. The aim was to develop baseline information for nursery production and landscape use that utilize reclaimed water for irrigation. Plants were irrigated weekly with a nutrient solution at an electrical conductivity (EC) of 1.0 dS·m−1 as control or a saline solution at an EC of 2.5, 5.0, 7.5, or 10.0 dS·m−1 for 8 weeks. Half of the plants were harvested after four irrigation events, and the remaining plants were harvested after eight irrigation events. At harvest, visual rating (0 = dead and 5 = excellent without foliage salt damage), plant width, number of shoots, leaf area, shoot dry weight, leaf greenness [Soil Plant Analysis Development (SPAD)], stomatal conductance, and canopy temperature were collected to assess the impact of salinity stress. In both species, salt damage was dependent on the salinity levels and length of exposure. After four irrigation events, both species exhibited foliage damage that increased in severity with rising EC. The most severe damage was observed in plants receiving saline solution at an EC of 10.0 dS·m−1. After eight irrigation events, P. davidsonii exposed to a saline solution with an EC of 10.0 dS·m−1 received a visual rating of 0, whereas P. heterophyllus had a visual rating of 0.4. Both species exhibited salinity-induced effects, with variations observed in the specific parameters and the degree of response. Penstemon davidsonii exhibited significant salinity stress, as indicated by reduced leaf area, shoot dry weight, SPAD reading, and stomatal conductance with increasing EC of the saline solution. In addition, in both species, at both harvests, canopy temperatures increased either linearly or quadratically by 8% to 36% as the EC levels of the saline solution increased. These results indicate that P. davidsonii was more sensitive to salinity stress than P. heterophyllus.

An assessment of the durability of untreated and water repellent-treated cultural heritage stone (Döğer tuff-Turkey) by salt mist and salt crystallization tests

Salt mist and salt crystallization tests were conducted to determine the resistance of the untreated and water-repellent-treated Döğer tuff samples to salt damage. The Döğer tuffs are of volcanic origin and consist of porous pyroclastic rocks. A series of characterization studies were performed to determine the physicochemical and chemical properties (XRF), mineralogical-petrographic characteristics (polarizing optical microscopy, XRD, and SEM), and pore-size distribution (MIP) of the Döğer tuff prior to the aging tests. Following the aging experiments, the changes in weight, ultrasound pulse velocity, uniaxial compressive strength, and variations in pore size distribution were examined in the tested tuffs. In addition, SEM studies were conducted to analyze the microstructures. The untreated tuff samples were more severely affected by salt crystallization. The increases in dry weight for untreated and water-repellent-treated Döğer tuff samples were 0.27% and 0.13% after 60 cycles of salt mist exposure and 7.2% and 3.76% after salt crystallization cycles using a sodium chloride solution, respectively. Both conditions resulted from the accumulation of NaCl crystals on the tuff surface and within the pores. Salt crystal formation in a sodium sulfate solution led to dry weight change of 2.02% and 0.29% in the untreated and water-repellent-treated samples, respectively. The uniaxial compressive strength of the untreated tuff samples decreased by 36.71% in the presence of sodium chloride solution and by 72.58% in the presence of sodium sulfate solution. The ultrasound pulse velocity values decreased in all tuff samples after the salt crystallization test. However, the Döğer tuff samples were still distinguishable after both tests and their physical integrity remained intact.

Salt damage on asphalt surfaces under repeated dissolution at molecular scale

Salt damage on asphalt surfaces is primarily attributed to migration of ions, with repeated dissolution exacerbating the degradation of asphalt performance. To investigate micro mechanism of salt corrosion on asphalt surfaces during repeated dissolution, this research uses molecular dynamics (MD) simulation and experiments to measure interactions among asphalt, salt, and water. Asphalt-salt systems and asphalt-water interfaces are built to calculate molecular damage behaviors by energies, mobilities, and distributions, along with micro-morphology and rheological properties of asphalt samples under salt corrosion. The interaction energies of salt with asphalt exhibit a hierarchy with Mg2+ ˃ Ca2+ ˃ Na+ and SO42- ˃ Cl-, predominantly governed by electrostatic energies. Repeated dissolution is a dynamic damage process. When water contacts on salt-eroded asphalt surfaces, salt ions migrate into water, forming solutions. Sulfates exhibit slower mobility and higher structural stability compared to chlorides, owing to smaller free volume, stronger interaction, and weaker water debonding. Rheologically, salt-eroded asphalt manifests as stiffer and tougher than water-eroded or base asphalt. These asphalt samples undergo softening and increased viscosity due to loss of salt ions. Consequently, compared to chlorides, sulfates demonstrate stronger interactions with asphalt and more difficulty in diffusing to water, resulting in severer damage on asphalt surfaces.