Curing the earth: A review of anthropogenic soil salinization and plant-based strategies for sustainable mitigation

The effect of AMF combined with biochar on plant growth and soil quality under saline-alkali stress: Insights from microbial community analysis

Arbuscular mycorrhizal fungi (AMF) and biochar application individually can enhance plant tolerance to saline-alkali stress and promote plant growth efficiency. However, little is known about the potential synergistic effects of their combination on improving plant growth and soil quality under saline-alkali stress. This experiment adopted the potted method to explore the effects of four treatments on switchgrass growth and soil quality: biochar (BC), Rhizophagus irregularis (Ri), biochar + Ri (BR) and a control without biochar or Ri (CK). Compared to the CK treatment, the switchgrass biomass increased by 92.4 %, 148.6 %, and 177.3 % in the BC, Ri, and BR treatment groups, respectively. Similarly, the rhizosphere soil quality index increased by 29.33 %, 22.7 %, and 49.1 % in the respective treatment groups. The BR treatment significantly altered the rhizosphere soil microbial composition and diversity. Notably, compared to the other treatments, the archaeal α-diversity in the BR group showed a significant decrease. BR treatment significantly increased the relative abundance of bacteria, fungi and archaea at the genus level (e.g., Bacillus, Trichome and candidatus_methanopenens). Network analysis showed that the complexity and closeness of interactions between different microbial taxa were stronger in the BC, Ri and BR treatments than in the CK treatment, with BR being the more prominent. In summary, biochar combined with Ri has a better effect on promoting the growth of switchgrass under saline-alkali stress, improving the quality of saline-alkali soil, and increasing soil microbial diversity. This study provides a new approach for the efficient development and utilization of saline-alkali land.

Effect of salt-alkali stress on seed germination of the halophyte Halostachys caspica

The increasing global phenomenon of soil salinization has prompted heightened interest in the physiological ecology of plant salt and alkali tolerance. Halostachys caspica belonging to Amaranthaceae, an exceptionally salt-tolerant halophyte, is widely distributed in the arid and saline-alkali regions of Xinjiang, in Northwest China. Soil salinization and alkalinization frequently co-occur in nature, but very few studies focus on the interactive effects of various salt and alkali stress on plants. In this study, the impacts on the H. caspica seed germination, germination recovery and seedling growth were investigated under the salt and alkali stress. The results showed that the seed germination percentage was not significantly reduced at low salinity at pH 5.30-9.60, but decreased with elevated salt concentration and pH. Immediately after, salt was removed, ungerminated seeds under high salt concentration treatment exhibited a higher recovery germination percentage, indicating seed germination of H. caspica was inhibited under the condition of high salt-alkali stress. Stepwise regression analysis indicated that, at the same salt concentrations, alkaline salts exerted a more severe inhibition on seed germination, compared to neutral salts. The detrimental effects of salinity or high pH alone were less serious than their combination. Salt concentration, pH value, and their interactions had inhibitory effects on seed germination, with salinity being the decisive factor, while pH played a secondary role in salt-alkali mixed stress.

Sensitivity of Daphnia spinulata Birabén, 1917 to glyphosate at different salinity levels

Daphnia spinulata Birabén, 1917 is an endemic cladoceran species, frequent in the zooplankton communities of the shallow lakes of the Pampean region of Argentina. These lakes have varying salinity levels and, being located in agricultural areas, are frequently subject to pesticide pollution. This study aimed to determine the effects of the herbicide glyphosate (Panzer Gold®) in combination with different salinity levels on the biological parameters of D. spinulata and its recovery ability after a short exposure. Three types of assays were performed: an acute toxicity test, a chronic assessment to determine survival, growth and reproduction, and recovery assays under optimal salinity conditions (1 g L-1). The LC50-48 h of glyphosate was 7.5 mg L-1 (CL 3.15 to 11.72). Longevity and the number of offspring and clutches were significantly reduced due to the combined exposure of glyphosate and increased salinity. The timing of the first offspring did not recover after glyphosate exposure. Our results reveal that D. spinulata is sensitive to the herbicide Panzer Gold® at concentrations well below those indicated in the safety data sheet of this commercial formulation, which causes stronger negative effects in conditions of higher salinity. Further research is needed to shed light on the sensitivity of this cladoceran to glyphosate and its variability under other interactive stress factors.

Arbuscular mycorrhizal fungi drive bacterial community assembly in halophyte Suaeda salsa

Halophytes inhabit saline soils, wherein most plants cannot grow, therefore, their ecological value is outstanding. Arbuscular mycorrhizal (AM) fungi can reconstruct microbial communities to assist plants with stress tolerance. However, little information is available on the microbial community assembly of AM fungi in halophytes. A pot experiment was conducted to investigate the effects of AM fungi on rhizosphere bacterial community structure and soil physiochemical characteristics in the halophyte Suaeda salsa at 0, 100, and 400 mM NaCl. The results demonstrated that AM fungi increased soil alkaline phosphatase (ALP) activity at the three NaCl concentrations, and decreased available P, available K, and the activity of soil catalase (CAT) at 100 mM NaCl. AM fungi decreased the Shannon index of the community at 0 and 100 mM NaCl and increased Sobs index at 400 mM NaCl. Regarding the bacterial community structure, AM fungi substantially decreased the abundance of Acidobacteria phylum at 0 and 100 mM NaCl. AM fungi significantly increased the abundance of genus Ramlibacter, an oxyanion-reducing bacteria that can clean out reactive oxygen species (ROS). AM fungi recruited the genera Massilia and Arthrobacter at 0 and 100 mM NaCl, respectively. Some strains in the two genera have been ascribed to plant growth promoting bacteria (PGPB). AM fungi increased the dry weight and promoted halophyte growth at all three NaCl levels. This study supplements the understanding that AM fungi assemble rhizosphere bacterial communities in halophytes.

The RING zinc finger protein LbRZF1 promotes salt gland development and salt tolerance in Limonium bicolor

The recretohalophyte Limonium bicolor thrives in high-salinity environments because salt glands on the above-ground parts of the plant help to expel excess salt. Here, we characterize a nucleus-localized C3HC4 (RING-HC)-type zinc finger protein of L. bicolor named  RING  ZINC  FINGER PROTEIN  1 (LbRZF1). LbRZF1 was expressed in salt glands and in response to NaCl treatment. LbRZF1 showed no E3 ubiquitin ligase activity. The phenotypes of overexpression and knockout lines for LbRZF1 indicated that LbRZF1 positively regulated salt gland development and salt tolerance in L. bicolor. lbrzf1 mutants had fewer salt glands and secreted less salt than did the wild-type, whereas LbRZF1-overexpressing lines had opposite phenotypes, in keeping with the overall salt tolerance of these plants. A yeast two-hybrid screen revealed that LbRZF1 interacted with LbCATALASE2 (LbCAT2) and the transcription factor LbMYB113, leading to their stabilization. Silencing of LbCAT2 or LbMYB113 decreased salt gland density and salt tolerance. The heterologous expression of LbRZF1 in Arabidopsis thaliana conferred salt tolerance to this non-halophyte. We also identified the transcription factor LbMYB48 as an upstream regulator of LbRZF1 transcription. The study of LbRZF1 in the regulation network of salt gland development also provides a good foundation for transforming crops and improving their salt resistance.

Genome-wide identification of bHLH transcription factors and functional analysis in salt gland development of the recretohalophyte sea lavender (Limonium bicolor)

Transcription factors with basic helix-loop-helix (bHLH) structures regulate plant growth, epidermal structure development, metabolic processes, and responses to stress extensively. Sea lavender (Limonium bicolor) is a recretohalophyte with unique salt glands in the epidermis that make it highly resistant to salt stress, contributing to the improvement of saline lands. However, the features of the bHLH transcription factor family in L. bicolor are largely unknown. Here, we systematically analyzed the characteristics, localization, and phylogenetic relationships of 187 identified bHLH family genes throughout the L. bicolor genome, as well as their cis-regulatory promoter elements, expression patterns, and key roles in salt gland development or salt tolerance by genetic analysis. Nine verified L. bicolor bHLH genes are expressed and the encoded proteins function in the nucleus, among which the proteins encoded by Lb2G14060 and Lb1G07934 also localize to salt glands. Analysis of CRISPR-Cas9-generated knockout mutants and overexpression lines indicated that the protein encoded by Lb1G07934 is involved in the formation of salt glands, salt secretion, and salt resistance, indicating that bHLH genes strongly influence epidermal structure development and stress responses. The current study lays the foundation for further investigation of the effects and functional mechanisms of bHLH genes in L. bicolor and paves the way for selecting salt-tolerance genes that will enhance salt resistance in crops and for the improvement of saline soils.

Functionally responsive hydrogels with salt-alkali sensitivity effectively target soil amelioration

The long-standing crisis of soil salinization and alkalization poses a significant challenge to global agricultural development. High soil salinity-alkalinity, water dispersion, and nutrient loss present major hurdles to soil improvement. Novel environmentally friendly gels have demonstrated excellent water retention and slow-release capabilities in agricultural enhancement. However, their application for improving saline-alkali soil is both scarce and competitive. This study proposes a new strategy for regulating saline-alkali soil using gel-coated controlled-release soil modifiers (CWR-SRMs), where radical-polymerized gels are embedded on the surface of composite gel beads through spray coating. Characterization and performance analysis reveal that the three-dimensional spatial network structure rich in hydrophilic groups exhibits good thermal stability (first-stage weight loss temperature of 257.7 °C in thermogravimetric analysis) and encapsulation efficiency for fulvic acid‑potassium (FA-K), which can enhance soil quality in saline-alkali environments. The molecular chain relaxation under saline-alkali conditions promotes a synergistic effect of swelling and slow release, endowing it with qualifications as a water reservoir, Ca2+ source unit, and slow-release body. The results of a 6 weeks incubation experiment on 0-20 cm saline-alkaline soil with different application gradients showed that the gradient content had a significant effect on the soil improvement effect. Specifically, the T2 (the dosage accounted for 1 % of soil mass) treatment significantly increases water retention (30 % ~ 90 %), and nutrient levels (30 % ~ 50 %), while significantly decreasing soil sodium colloid content (30 % ~ 60 %) and soil pH (10 % ~ 15 %). Furthermore, PCA analysis indicates that the addition of 1 % CWR-SRMs as amendments can significantly adjust the negative aspects of soil salinity and alkalinity. This highlights the excellent applicability of CWR-SRMs in improving saline-alkali agricultural ecosystems, demonstrating the potential value of novel environmentally friendly gels as an alternative solution for soil challenges persistently affected by adverse salinity and alkalinity.

Knowledge gaps on how to adapt crop production under changing saline circumstances in the Netherlands

Salinization, the increase and accumulation of salts in water and soil, impacts productivity of arable crops and is exacerbated by climate change. The Netherlands, like several other deltas and semi-arid regions, faces increasing salinization that negatively impacts agriculture and freshwater availability. Although a lot of salinity expertise exist in the Netherlands, several knowledge gaps on the impact of salinization in the Netherlands, as well as steps to facilitate closing this knowledge gaps to improve saline agriculture in the Netherlands, still exist. This review/opinion article moves beyond existing papers on salinization in bringing together various adaptation measures by thoroughly reviewing the measures through a triple P (People, Planet, Profit) lens. Five main salinity adaptation measures of the crop-soil-water continuum are 1) breeding and selection of salt tolerant varieties, 2) increased cultivation of halophytes, 3) soil management interventions, 4) use of biostimulants, and 5) irrigation techniques. These adaptation measures are described, discussed and analysed for their compliance to the sustainable development elements People, Planet and Profit. All five adaptation measures have potential positive impact on livelihood, contribute to food security and generate revenue but on the other hand, these measures may contribute to unwarranted changes of the ecosystem. The paper ends with a concluding chapter in which the bottlenecks and knowledge gaps that need resolving are identified based on the critical, including triple P, assessment of the discussed adaptation measures. Three key knowledge gaps on breeding, agronomy, environmental sciences and socioeconomics are identified with several approaches that lead to insights elucidated. Thereby informing on future research and action plans to optimize implementation of salinity adaptation measures in the Netherlands.

Characteristic microbiome and synergistic mechanism by engineering agent MAB-1 to evaluate oil-contaminated soil biodegradation in different layer soil

Bioremediation is a sustainable and pollution-free technology for crude oil-contaminated soil. However, most studies are limited to the remediation of shallow crude oil-contaminated soil, while ignoring the deeper soil. Here, a high-efficiency composite microbial agent MAB-1 was provided containing Bacillus (naphthalene and pyrene), Acinetobacter (cyclohexane), and Microbacterium (xylene) to be synergism degradation of crude oil components combined with other treatments. According to the crude oil degradation rate, the up-layer (63.64%), middle-layer (50.84%), and underlying-layer (54.21%) crude oil-contaminated soil are suitable for bioaugmentation (BA), biostimulation (BS), and biostimulation+bioventing (BS+BV), respectively. Combined with GC-MS and carbon number distribution analysis, under the optimal biotreatment, the degradation rates of 2-ring and 3-ring PAHs in layers soil were about 70% and 45%, respectively, and the medium and long-chain alkanes were reduced during the remediation. More importantly, the relative abundance of bacteria associated with crude oil degradation increased in each layer after the optimal treatment, such as Microbacterium (2.10-14%), Bacillus (2.56-12.1%), and Acinetobacter (0.95-12.15%) in the up-layer soil; Rhodococcus (1.5-6.9%) in the middle-layer soil; and Pseudomonas (3-5.4%) and Rhodococcus (1.3-13.2%) in the underlying-layer soil. Our evaluation results demonstrated that crude oil removal can be accelerated by adopting appropriate bioremediation approach for different depths of soil, providing a new perspective for the remediation of actual crude oil-contaminated sites.

Salt Tolerance in Machilus faberi: Elucidating Growth and Physiological Adaptations to Saline Environments

Adversity stress is the main environmental factor limiting plant growth and development, including salt and other stress factors. This study delves into the adaptability and salt tolerance mechanisms of Machilus faberi Hemsl, a species with potential for cultivation in salinized areas. We subjected the plants to various salt concentrations to observe their growth responses and to assess key physiological and biochemical indicators. The results revealed that under high salt concentrations (500 and 700 mmol-1/L), symptoms such as leaf yellowing, wilting, and eventual death were observed. Notably, plant height and shoot growth ceased on the 14th day of exposure. Chlorophyll content (a, b, total a + b, and the a/b ratio) initially increased but subsequently decreased under varying levels of salt stress. Similarly, the net photosynthetic rate, stomatal conductance, leaf water content, and root activity significantly declined under these conditions. Moreover, we observed an increase in malondialdehyde levels and relative conductivity, indicative of cellular damage and stress. The activity of superoxide dismutase and ascorbate peroxidase initially increased and then diminished with prolonged stress, whereas peroxidase activity consistently increased. Levels of proline and soluble protein exhibited an upward trend, contrasting with the fluctuating pattern of soluble sugars, which decreased initially but increased subsequently. In conclusion, M. faberi exhibits a degree of tolerance to salt stress, albeit with growth limitations when concentrations exceed 300 mmol-1/L. These results shed light on the plant's mechanisms of responding to salt stress and provide a theoretical foundation for its cultivation and application in salt-affected regions.

Understanding AP2/ERF Transcription Factor Responses and Tolerance to Various Abiotic Stresses in Plants: A Comprehensive Review

Abiotic stress is an adverse environmental factor that severely affects plant growth and development, and plants have developed complex regulatory mechanisms to adapt to these unfavourable conditions through long-term evolution. In recent years, many transcription factor families of genes have been identified to regulate the ability of plants to respond to abiotic stresses. Among them, the AP2/ERF (APETALA2/ethylene responsive factor) family is a large class of plant-specific proteins that regulate plant response to abiotic stresses and can also play a role in regulating plant growth and development. This paper reviews the structural features and classification of AP2/ERF transcription factors that are involved in transcriptional regulation, reciprocal proteins, downstream genes, and hormone-dependent signalling and hormone-independent signalling pathways in response to abiotic stress. The AP2/ERF transcription factors can synergise with hormone signalling to form cross-regulatory networks in response to and tolerance of abiotic stresses. Many of the AP2/ERF transcription factors activate the expression of abiotic stress-responsive genes that are dependent or independent of abscisic acid and ethylene in response to abscisic acid and ethylene. In addition, the AP2/ERF transcription factors are involved in gibberellin, auxin, brassinosteroid, and cytokinin-mediated abiotic stress responses. The study of AP2/ERF transcription factors and interacting proteins, as well as the identification of their downstream target genes, can provide us with a more comprehensive understanding of the mechanism of plant action in response to abiotic stress, which can improve plants' ability to tolerate abiotic stress and provide a more theoretical basis for increasing plant yield under abiotic stress.

The transmembrane protein LbRSG from the recretohalophyte Limonium bicolor enhances salt gland development and salt tolerance

Salt glands are the unique epidermal structures present in recretohalophytes, plants that actively excrete excess Na+ by salt secretory structures to avoid salt damage. Here, we describe a transmembrane protein that localizes to the plasma membrane of the recretohalophyte Limonium bicolor. As virus-induced gene silencing of the corresponding gene LbRSG in L. bicolor decreased the number of salt glands, we named the gene Reduced Salt Gland. We detected LbRSG transcripts in salt glands by in situ hybridization and transient transformation. Overexpression and silencing of LbRSG in L. bicolor pointed to a positive role in salt gland development and salt secretion by interacting with Lb3G16832. Heterologous LbRSG expression in Arabidopsis enhanced salt tolerance during germination and the seedling stage by alleviating NaCl-induced ion stress and osmotic stress after replacing or deleting the (highly) negatively charged region of extramembranous loop. After screened by immunoprecipitation-mass spectrometry and verified using yeast two-hybrid, PGK1 and BGLU18 were proposed to interact with LbRSG to strengthen salt tolerance. Therefore, we identified (highly) negatively charged regions in the extramembrane loop that may play an essential role in salt tolerance, offering hints about LbRSG function and its potential to confer salt resistance.

Melatonin-mediated CcARP1 alters F-actin dynamics by phosphorylation of CcADF9 to balance root growth and salt tolerance in pigeon pea

As a multifunctional hormone-like molecule, melatonin exhibits a pleiotropic role in plant salt stress tolerance. While actin cytoskeleton is essential to plant tolerance to salt stress, it is unclear if and how actin cytoskeleton participates in the melatonin-mediated alleviation of plant salt stress. Here, we report that melatonin alleviates salt stress damage in pigeon pea by activating a kinase-like protein, which interacts with an actin-depolymerizing factor. Cajanus cajan Actin-Depolymerizing Factor 9 (CcADF9) has the function of severing actin filaments and is highly expressed under salt stress. The CcADF9 overexpression lines (CcADF9-OE) showed a reduction of transgenic root length and an increased sensitivity to salt stress. By using CcADF9 as a bait to screen an Y2H library, we identified actin depolymerizing factor-related phosphokinase 1 (ARP1), a novel protein kinase that interacts with CcADF9. CcARP1, induced by melatonin, promotes salt resistance of pigeon pea through phosphorylating CcADF9, inhibiting its severing activity. The CcARP1 overexpression lines (CcARP1-OE) displayed an increased transgenic root length and resistance to salt stress, whereas CcARP1 RNA interference lines (CcARP1-RNAi) presented the opposite phenotype. Altogether, our findings reveal that melatonin-induced CcARP1 maintains F-actin dynamics balance by phosphorylating CcADF9, thereby promoting root growth and enhancing salt tolerance.

Waste seaweed compost and rhizosphere bacteria Pseudomonas koreensis promote tomato seedlings growth by benefiting properties, enzyme activities and rhizosphere bacterial community in coastal saline soil of Yellow River Delta, China

This study investigated the effects of waste seaweed compost and rhizosphere bacteria Pseudomonas koreensis HCH2-3 on the tomato seedlings growth in coastal saline soils and chemical properties, enzyme activities, microbial communities of rhizosphere soil. Microcosmic experiment showed that the seaweed compost and rhizosphere bacteria (SC + HCH2-3) significantly alleviated the negative effects of salinity on the growth of tomato seedlings. SC + HCH2-3 amendment significantly increased the plant height and root fresh biomass of tomato seedling by 105.59% and 55.60% in the coastal saline soils, respectively. The soil properties and enzyme activities were also dramatically increased, indicating that the nutrient status of coastal saline soil was improved by SC + HCH2-3 amendment. In addition, Proteobacteria, Actinobacteriota and Firmicutes were the dominant phyla in the rhizosphere soil after adding seaweed compost and rhizosphere bacteria P. koreensis HCH2-3. The relative abundances of Massilia, Azospira, Pseudomonas and Bacillus increased in treatment SC + HCH2-3. Especially, the beneficial bacteria genera, such as Pseudomonas, Bacillus and Azospira, were significantly correlated with the increases of contents of total nitrogen, nitrate nitrogen and ammonium nitrogen in tomato rhizosphere soil samples. Consequently, adding waste seaweed compost and rhizosphere bacteria P. koreensis HCH2-3 into coastal saline soil was suggested as an effective method to relieve salt stress of tomato plants.

Promotion of Ca2+ Accumulation in Roots by Exogenous Brassinosteroids as a Key Mechanism for Their Enhancement of Plant Salt Tolerance: A Meta-Analysis and Systematic Review

Brassinosteroids (BRs), the sixth major phytohormone, can regulate plant salt tolerance. Many studies have been conducted to investigate the effects of BRs on plant salt tolerance, generating a large amount of research data. However, a meta-analysis on regulating plant salt tolerance by BRs has not been reported. Therefore, this study conducted a meta-analysis of 132 studies to elucidate the most critical physiological mechanisms by which BRs regulate salt tolerance in plants from a higher dimension and analyze the best ways to apply BRs. The results showed that exogenous BRs significantly increased germination, plant height, root length, and biomass (total dry weight was the largest) of plants under salt stress. There was no significant difference between seed soaking and foliar spraying. However, the medium method (germination stage) and stem application (seedling stage) may be more effective in improving plant salt tolerance. BRs only inhibit germination in Solanaceae. BRs (2 μM), seed soaking for 12 h, and simultaneous treatment with salt stress had the highest germination rate. At the seedling stage, the activity of Brassinolide (C28H48O6) was higher than that of Homobrassinolide (C29H50O6), and post-treatment, BRs (0.02 μM) was the best solution. BRs are unsuitable for use in the germination stage when Sodium chloride is below 100 mM, and the effect is also weakest in the seedling stage. Exogenous BRs promoted photosynthesis, and antioxidant enzyme activity increased the accumulation of osmoregulatory and antioxidant substances and reduced the content of harmful substances and Na+, thus reducing cell damage and improving plant salt tolerance. BRs induced the most soluble protein, chlorophyll a, stomatal conductance, net photosynthetic rate, Glutathione peroxidase, and root-Ca2+, with BRs causing Ca2+ signals in roots probably constituting the most important reason for improving salt tolerance. BRs first promoted the accumulation of Ca2+ in roots, which increased the content of the above vital substances and enzyme activities through the Ca2+ signaling pathway, improving plant salt tolerance.

Effect of planting salt-tolerant legumes on coastal saline soil nutrient availability and microbial communities

Soil salinization is a serious global environmental problem affecting sustainable development of agriculture. Legumes are excellent candidates for the phytoremediation of saline soils; however, how soil microbes mediate the amelioration of coastal saline ecosystems is unknown. In this study, two salt-tolerant legumes, Glycine soja and Sesbania cannabina were planted in coastal saline soil for three years. Soil nutrient availability and microbiota structure (including bacteria, fungi, and diazotrophs) were compared between the phytoremediated soils and control soil (barren land). Planting legumes reduced soil salinity, and increased total carbon, total nitrogen, and NO3--N contents. Among the soil microbiota, some nitrogen-fixing bacteria (e.g., Azotobacter) were enriched in legumes, which were probably responsible for soil nitrogen accumulation. The complexity of the bacterial, fungal, and diazotrophic networks increased significantly from the control to the phytoremediated soils, suggesting that the soil microbial community formed closer ecological interactions during remediation. Furthermore, the dominant microbial functions were chemoheterotrophy (24.75%) and aerobic chemoheterotrophy (21.97%) involved in the carbon cycle, followed by nitrification (13.68%) and aerobic ammonia oxidation (13.34%) involved in the nitrogen cycle. Overall, our findings suggested that G. soja and S. cannabina legumes were suitable for ameliorating saline soils as they decreased soil salinity and increased soil nutrient content, with microorganisms especially nitrogen-fixing bacteria, playing an important role in this remediation process.

The Anthropogenic Salt Cycle

Increasing salt production and use is shifting the natural balances of salt ions across Earth systems, causing interrelated effects across biophysical systems collectively known as freshwater salinization syndrome. In this Review, we conceptualize the natural salt cycle and synthesize increasing global trends of salt production and riverine salt concentrations and fluxes. The natural salt cycle is primarily driven by relatively slow geologic and hydrologic processes that bring different salts to the surface of the Earth. Anthropogenic activities have accelerated the processes, timescales and magnitudes of salt fluxes and altered their directionality, creating an anthropogenic salt cycle. Global salt production has increased rapidly over the past century for different salts, with approximately 300 Mt of NaCl produced per year. A salt budget for the USA suggests that salt fluxes in rivers can be within similar orders of magnitude as anthropogenic salt fluxes, and there can be substantial accumulation of salt in watersheds. Excess salt propagates along the anthropogenic salt cycle, causing freshwater salinization syndrome to extend beyond freshwater supplies and affect food and energy production, air quality, human health and infrastructure. There is a need to identify environmental limits and thresholds for salt ions and reduce salinization before planetary boundaries are exceeded, causing serious or irreversible damage across Earth systems.

The Morphological Parameters and Cytosolic pH of Cells of Root Zones in Tobacco Plants (Nicotiana tabacum L.): Nonlinear Effects of NaCl Concentrations

Salinity impacts important processes in plants, reducing their yield. The effect of salinity on the cytosolic pH (pHcyt) has been little studied. In this research, we employed transgenic tobacco plants expressing the pH sensor Pt-GFP to investigate the alterations in pHcyt in cells across various root zones. Furthermore, we examined a wide spectrum of NaCl concentrations (ranging from 0 to 150 mM) and assessed morphological parameters and plant development. Our findings revealed a pattern of cytosolic acidification in cells across all root zones at lower NaCl concentrations (50, 100 mM). Interestingly, at 150 mM NaCl, pHcyt levels either increased or returned to normal, indicating a nonlinear effect of salinity on pHcyt. Most studied parameters related to development and morphology exhibited an inhibitory influence in response to NaCl. Notably, a nonlinear relationship was observed in the cell length within the elongation and differentiation zones. While cell elongation occurred at 50 and 100 mM NaCl, it was not evident at 150 mM NaCl. This suggests a complex interplay between stimulating and inhibitory effects of salinity, contributing to the nonlinear relationship observed between pHcyt, cell length, and NaCl concentration.

How Does Zinc Improve Salinity Tolerance? Mechanisms and Future Prospects

Salinity stress (SS) is a serious abiotic stress and a major constraint to agricultural productivity across the globe. High SS negatively affects plant growth and yield by altering soil physio-chemical properties and plant physiological, biochemical, and molecular processes. The application of micronutrients is considered an important practice to mitigate the adverse effects of SS. Zinc (Zn) is an important nutrient that plays an imperative role in plant growth, and it could also help alleviate the effects of salt stress. Zn application improves seed germination, seedling growth, water uptake, plant water relations, nutrient uptake, and nutrient homeostasis, therefore improving plant performance and saline conditions. Zn application also protects the photosynthetic apparatus from salinity-induced oxidative stress and improves stomata movement, chlorophyll synthesis, carbon fixation, and osmolytes and hormone accumulation. Moreover, Zn application also increases the synthesis of secondary metabolites and the expression of stress responsive genes and stimulates antioxidant activities to counter the toxic effects of salt stress. Therefore, to better understand the role of Zn in plants under SS, we have discussed the various mechanisms by which Zn induces salinity tolerance in plants. We have also identified diverse research gaps that must be filled in future research programs. The present review article will fill the knowledge gaps on the role of Zn in mitigating salinity stress. This review will also help readers to learn more about the role of Zn and will provide new suggestions on how this knowledge can be used to develop salt tolerance in plants by using Zn.

Transcription Factor GmERF105 Negatively Regulates Salt Stress Tolerance in Arabidopsis thaliana

The Ethylene Response Factor (ERF) transcription factors form a subfamily of the AP2/ERF family that is instrumental in mediating plant responses to diverse abiotic stressors. Herein, we present the isolation and characterization of the GmERF105 gene from Williams 82 (W82), which is rapidly induced by salt, drought, and abscisic acid (ABA) treatments in soybean. The GmERF105 protein contains an AP2 domain and localizes to the nucleus. GmERF105 was selectively bound to GCC-box by gel migration experiments. Under salt stress, overexpression of GmERF105 in Arabidopsis significantly reduced seed germination rate, fresh weight, and antioxidant enzyme activity; meanwhile, sodium ion content, malonic dialdehyde (MDA) content, and reactive oxygen species (ROS) levels were markedly elevated compared to the wild type. It was further found that the transcription levels of CSD1 and CDS2 of two SOD genes were reduced in OE lines. Furthermore, the GmERF105 transgenic plants displayed suppressed expression of stress response marker genes, including KIN1, LEA14, NCED3, RD29A, and COR15A/B, under salt treatment. Our findings suggest that GmERF105 can act as a negative regulator in plant salt tolerance pathways by affecting ROS scavenging systems and the transcription of stress response marker genes.

Physiological effects of combined NaCl and NaHCO3 stress on the seedlings of two maple species

Salt stress impacts growth and physiological processes in plants, and some plants exposed to salt stress will produce physiological mechanisms to adapt to the new environment. However, the effects of combined NaCl and NaHCO3 stress on the seedlings of Acer species are understudied. In this study, we designed an experiment to measure physiological characteristics by establishing a range of NaCl and NaHCO₃ concentrations (0, 25, 50, 75, and 100 mmol L^-1) to estimate the compound salt tolerance of Acer ginnala and Acer palmatum. When the concentrations of NaCl and NaHCO₃ were 25 mmol L^-1, the leaf water content, relative conductivity, malondialdehyde (MDA) content, proline content, soluble sugar content, and chlorophyll did not change (p > 0.05) in two maple seedlings. At concentrations greater than 50 mmol L^-1, the relative conductivity and MDA content increased, proline and soluble sugars accumulated, and the potential activity of PS II (F_v/F_o), potential photochemical efficiency of PS II (F_v/F_m), PS II actual photochemical efficiency (Yield), and photosynthetic electron transfer efficiency (ETR) decreased (p < 0.05). The superoxide dismutase (SOD) and catalase (CAT) activities showed the same trend of first increasing and then decreasing (p < 0.05). The peroxidase (POD) activity increased only when concentrations of NaCl and NaHCO₃ were 100 mmol L^-1, while there was no statistical difference between the other treatments and the control. Therefore, the two maple seedlings adjusted their osmotic balance and alleviated oxidative stress by accumulating proline, soluble sugars and increasing CAT and SOD activities. Further analysis showed that both species are salt tolerant and the salt tolerance of Acer ginnala is better than that of Acer palmatum.

Improving the monitoring of root zone soil salinity under vegetation cover conditions by combining canopy spectral information and crop growth parameters

Soil salinization is one of the main causes of land degradation in arid and semi-arid areas. Timely and accurate monitoring of soil salinity in different areas is a prerequisite for amelioration. Hyperspectral technology has been widely used in soil salinity monitoring due to its high efficiency and rapidity. However, vegetation cover is an inevitable interference in the direct acquisition of soil spectra during crop growth period, which greatly limits the monitoring of soil salinity by remote sensing. Due to high soil salinity could lead to difficulty in plants' water absorption, and inhibit plant dry matter accumulation, a method for monitoring root zone soil salinity by combining vegetation canopy spectral information and crop aboveground growth parameters was proposed in this study. The canopy spectral information was acquired by a spectroradiometer, and then variable importance in projection (VIP), competitive adaptive reweighted sampling (CARS), and random frog algorithm (RFA) were used to extract the salinity spectral features in cotton canopy spectrum. The extracted features were then used to estimate root zone soil salinity in cotton field by combining with cotton plant height, aboveground biomass, and shoot water content. The results showed that there was a negative correlation between plant height/aboveground biomass/shoot water content and soil salinity in 0-20, 0-40, and 0-60 cm soil layers at different growth stages of cotton. Spectral feature selection by the three methods all improved the prediction accuracy of soil salinity, especially CARS. The prediction accuracy based on the combination of spectral features and cotton growth parameters was significantly higher than that based on only spectral features, with R² increasing by 10.01%, 18.35%, and 29.90% for the 0-20, 0-40, and 0-60 cm soil layer, respectively. The model constructed based on the first derivative spectral preprocessing, spectral feature selection by CARS, cotton plant height, and shoot water content had the highest accuracy for each soil layer, with R² of 0.715,0.769, and 0.742 for the 0-20, 0-40, 0-60 cm soil layer, respectively. Therefore, the method by combining cotton canopy hyperspectral data and plant growth parameters could significantly improve the prediction accuracy of root zone soil salinity under vegetation cover conditions. This is of great significance for the amelioration of saline soil in salinized farmlands arid areas.

The Potential of CRISPR/Cas Technology to Enhance Crop Performance on Adverse Soil Conditions

Worldwide food security is under threat in the actual scenery of global climate change because the major staple food crops are not adapted to hostile climatic and soil conditions. Significant efforts have been performed to maintain the actual yield of crops, using traditional breeding and innovative molecular techniques to assist them. However, additional strategies are necessary to achieve the future food demand. Clustered regularly interspaced short palindromic repeat/CRISPR-associated protein (CRISPR/Cas) technology, as well as its variants, have emerged as alternatives to transgenic plant breeding. This novelty has helped to accelerate the necessary modifications in major crops to confront the impact of abiotic stress on agriculture systems. This review summarizes the current advances in CRISPR/Cas applications in crops to deal with the main hostile soil conditions, such as drought, flooding and waterlogging, salinity, heavy metals, and nutrient deficiencies. In addition, the potential of extremophytes as a reservoir of new molecular mechanisms for abiotic stress tolerance, as well as their orthologue identification and edition in crops, is shown. Moreover, the future challenges and prospects related to CRISPR/Cas technology issues, legal regulations, and customer acceptance will be discussed.

Evaporative destabilization of a salt crust with branched pattern formation

The impact of salt crust formation over porous media on water evaporation is an important issue in relation with the water cycle, agriculture, building sciences and more. The salt crust is not a simple accumulation of salt crystals at the porous medium surface but undergoes complex dynamics with possible air gap formation between the crust and the porous medium surface. We report on experiments that allow to identify various crust evolution regimes depending on the competition between evaporation and vapor condensation. The various regimes are summarized in a diagram. We focus on the regime where dissolution-precipitation processes lead to the upward displacement of the salt crust and the generation of a branched pattern. It is shown that the branched pattern results from the crust upper surface destabilization whereas the crust lower surface remains essentially flat. We show that the resulting branched efflorescence salt crust is heterogeneous with a greater porosity in the salt fingers. This leads to the preferential drying of the salt fingers followed by a period in which the crust morphology change only occurs in the salt crust lower region. The salt crust eventually tends toward a frozen state where no visible change occurs in the salt crust morphology, but without blocking the evaporation. These findings provide in-depth insights into the salt crust dynamics and pave the way for the better understanding of the impact of efflorescence salt crusts on evaporation and the development of predictive models.

GmGSTU23 Encoding a Tau Class Glutathione S-Transferase Protein Enhances the Salt Tolerance of Soybean (Glycine max L.)

Salt stress has a detrimental impact on crop yield, quality, and profitability. The tau-like glutathione transferases (GSTs) represent a significant group of enzymes that play a crucial role in plant stress responses, including salt stress. In this study, we identified a tau-like glutathione transferase family gene from soybean named GmGSTU23. Expression pattern analysis revealed that GmGSTU23 was predominantly expressed in the roots and flowers and exhibited a concentration–time-specific pattern in response to salt stress. Transgenic lines were generated and subjected to phenotypic characterization under salt stress. The transgenic lines exhibited increased salt tolerance, root length, and fresh weight compared to the wild type. Antioxidant enzyme activity and malondialdehyde content were subsequently measured, and the data revealed no significant differences between the transgenic and wild-type plants in the absence of salt stress. However, under salt stress, the wild-type plants exhibited significantly lower activities of SOD, POD, and CAT than the three transgenic lines, whereas the activity of APX and the content of MDA showed the opposite trend. We identified changes in glutathione pools and associated enzyme activity to gain insights into the underlying mechanisms of the observed phenotypic differences. Notably, under salt stress, the transgenic Arabidopsis’s GST activity, GR activity, and GSH content were significantly higher than those of the wild type. In summary, our findings suggest that GmGSTU23 mediates the scavenging of reactive oxygen species and glutathione by enhancing the activity of glutathione transferase, thereby conferring enhanced tolerance to salt stress in plants.

Microneedle-Coupled Epidermal Sensors for In-Situ-Multiplexed Ion Detection in Interstitial Fluids

Maintaining the concentrations of various ions in body fluids is critical to all living organisms. In this contribution, we designed a flexible microneedle patch coupled electrode array (MNP-EA) for the in situ multiplexed detection of ion species (Na⁺, K⁺, Ca²⁺, and H⁺) in tissue interstitial fluid (ISF). The microneedles (MNs) are mechanically robust for skin or cuticle penetration (0.21 N/needle) and highly swellable to quickly extract sufficient ISF onto the ion-selective electrochemical electrodes (∼6.87 μL/needle in 5 min). The potentiometric sensor can simultaneously detect these ion species with nearly Nernstian response in the ranges wider enough for diagnosis purposes (Na⁺: 0.75-200 mM, K⁺: 1-128 mM, Ca²⁺: 0.25-4.25 mM, pH: 5.5-8.5). The in vivo experiments on mice, humans, and plants demonstrate the feasibility of MNP-EA for timely and convenient diagnosis of ion imbalances with minimal invasiveness. This transdermal sensing platform shall be instrumental to home-based diagnosis and health monitoring of chronic diseases and is also promising for smart agriculture and the study of plant biology.

Genome-wide analysis of TPX2 gene family in Populus trichocarpa and its specific response genes under various abiotic stresses

Microtubules are essential for regulating cell morphogenesis, plant growth, and the response of plants to abiotic stresses. TPX2 proteins are the main players determining the spatiotemporally dynamic nature of the MTs. However, how TPX2 members respond to abiotic stresses in poplar remains largely unknown. Herein, 19 TPX2 family members were identified from the poplar genome and analyzed the structural characteristics as well as gene expression patterns. All TPX2 members had the conserved structural characteristics, but exhibited different expression profiles in different tissues, indicating their varying roles during plant growth. Additionally, several light, hormone, and abiotic stress responsive cis-acting regulatory elements were detected on the promoters of PtTPX2 genes. Furthermore, expression analysis in various tissues of Populus trichocarpa showed that the PtTPX2 genes responded differently to heat, drought and salt stress. In summary, these results provide a comprehensive analysis for the TPX2 gene family in poplar and an effective contribution to revealing the mechanisms of PtTPX2 in the regulatory network of abiotic stress.

Stress Management in Plants: Examining Provisional and Unique Dose-Dependent Responses

The purpose of this review is to critically evaluate the effects of different stress factors on higher plants, with particular attention given to the typical and unique dose-dependent responses that are essential for plant growth and development. Specifically, this review highlights the impact of stress on genome instability, including DNA damage and the molecular, physiological, and biochemical mechanisms that generate these effects. We provide an overview of the current understanding of predictable and unique dose-dependent trends in plant survival when exposed to low or high doses of stress. Understanding both the negative and positive impacts of stress responses, including genome instability, can provide insights into how plants react to different levels of stress, yielding more accurate predictions of their behavior in the natural environment. Applying the acquired knowledge can lead to improved crop productivity and potential development of more resilient plant varieties, ensuring a sustainable food source for the rapidly growing global population.

Screening Wetland and Forage Plants for Phytoremediation of Salt-Affected Soils in the Vietnamese Mekong Delta

This study evaluated the salt tolerance and sodium (Na) bioaccumulation of Typha orientalis, Lepironia articulata, Eleocharis dulcis, Scirpus littoralis, Brachiaria mutica, Paspalum atratum and Setaria sphacelata at five salinity levels of 0, 5, 10, 15 and 20‰ (corresponding to 0, 2.4, 6.9, 12.6 and 18 g NaCl L^-1). S. littoralis showed zero-reduction in total dry biomass and was classified as a salt tolerant plant based on the membership function value. The highest Na⁺ accumulation was observed in S. sphacelata (307.9 mg plant^-1) in spite of its salt sensitivity, followed by S. littoralis and T. orientalis at concentration of 155 mg plant^-1. Consequently, the Na⁺ phytoextraction potential of these species can be estimated as 46.2, 23.3 and 23.3 kg ha^-1 over 49 days, respectively. Taken together, they show high potential as Na⁺ hyperaccumulators, and can be selected in the national reclamation program for salt-affected soils in the context adaptation to climate change.

Symbiotic System Establishment between Piriformospora indica and Glycine max and Its Effects on the Antioxidant Activity and Ion-Transporter-Related Gene Expression in Soybean under Salt Stress

The utilization of symbiosis with beneficial microorganisms has considerable potential for increasing growth and resistance under abiotic stress. The endophytic root fungus Piriformospora indica has been shown to improve plant growth under salt and drought stress in diverse plant species, while there have been few reports of the interaction of P. indica with soybean under salt stress. In this study, the symbiotic system of P. indica and soybean (Glycine max L.) was established, and the effect of P. indica on soybean growth and salt tolerance was investigated. The colonized and non-colonized soybeans were subjected to salt stress (200 mmol/L NaCl), and the impairments in chlorophyll and increasing relative conductivity that can be caused by salt stress were alleviated in the P. indica-colonized plants. The accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion (O2−) were lower than that in non-colonized plants under salt treatment, whereas the activities of antioxidant enzymes were significantly increased by P. indica colonization, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione reductase (GR). Importantly, without salt treatment, the Na+ concentration was lower, and the K+ concentration was higher in the roots compared with non-colonized plants. Differential expressions of ion transporter genes were found in soybean roots after P. indica colonization. The P. indica colonization positively regulated the transcription level of PM H+-ATPase, SOS1, and SOS2. The study shows that P. indica enhances the growth and salt tolerance of soybean, providing a strategy for the agricultural production of soybean plants in saline-alkali soils.

Geological controls on evolution of evaporative precipitates on soil-free substrates and ecosystems, southern New Zealand

Soil-free bare substrates have formed by natural and human-induced processes in a semi-arid rain shadow, in the lee of actively rising mountains. These substrates have developed evaporative salt encrustations with a wide range of minerals controlled by local substrate permeability and mineralogy. Many of these small (hectare scale) sites also host endemic salt-tolerant ecosystems that are currently endangered by weed incursion. This study characterises the differing mineralogy and geochemistry of these rare ecosystem-hosting substrates. Impermeable substrates, especially clay-rich schist basement, are dominated by NaCl from marine aerosols in rain. The high Na at these sites further enhances impermeability of substrates by promoting surficial clay mobility, so that even Pleistocene-Recent sediments derived from schist basement develop evaporative crusts. The Na/Cl ratio of some of these substrates, especially sediments, has been increased by alteration of albite. However, mineralogically similar greywacke-derived sediments do not develop saline encrustations. Penetration of rainwater into substrates facilitates water-rock interaction reactions that yield entirely different evaporative salt mineralogy, as the NaCl component is overshadowed by constituents dissolved from the rocks. Schist basement and limestone-rich substrates develop carbonate-dominated evaporites, especially calcite, and associated waters are typically supersaturated with respect to carbonate minerals. Some sulphate-rich evaporites form where rock pyrite has been oxidised. Hydrothermally altered schist basement is locally enriched in Mg-bearing carbonates, sulphides and gold. Bare substrates on these sites are variably permeable and develop evaporative salts with carbonates, sulphates, ferric oxyhydroxide (some arsenic-bearing), and minor brucite, after extensive water-rock interaction. Most of the sites are alkaline, and pH locally exceeds 10, as a result of the combinations of evaporative processes and water-rock interactions. The specialist plants have evolved to tolerate the relatively high salinities and pH of these chemically distinctive sites.

Engineering drought and salinity tolerance traits in crops through CRISPR-mediated genome editing: Targets, tools, challenges, and perspectives

Prolonged periods of drought triggered by climate change hamper plant growth and cause substantial agricultural yield losses every year. In addition to drought, salinity is one of the major abiotic stresses that severely affect crop health and agricultural production. Plant responses to drought and salinity involve multiple processes that operate in a spatiotemporal manner, such as stress sensing, perception, epigenetic modifications, transcription, post-transcriptional processing, translation, and post-translational changes. Consequently, drought and salinity stress tolerance are polygenic traits influenced by genome-environment interactions. One of the ideal solutions to these challenges is the development of high-yielding crop varieties with enhanced stress tolerance, together with improved agricultural practices. Recently, genome-editing technologies, especially clustered regularly interspaced short palindromic repeats (CRISPR) tools, have been effectively applied to elucidate how plants deal with drought and saline environments. In this work, we aim to portray that the combined use of CRISPR-based genome engineering tools and modern genomic-assisted breeding approaches are gaining momentum in identifying genetic determinants of complex traits for crop improvement. This review provides a synopsis of plant responses to drought and salinity stresses at the morphological, physiological, and molecular levels. We also highlight recent advances in CRISPR-based tools and their use in understanding the multi-level nature of plant adaptations to drought and salinity stress. Integrating CRISPR tools with modern breeding approaches is ideal for identifying genetic factors that regulate plant stress-response pathways and for the introgression of beneficial traits to develop stress-resilient crops.

LbMYB48 positively regulates salt gland development of Limonium bicolor and salt tolerance of plants

Limonium bicolor is a dicotyledonous recretohalophyte with several multicellular salt glands on the leaves. The plant can directly secrete excess salt onto the leaf surface through the salt glands to maintain ion homeostasis under salt stress. Therefore, it is of great significance to study the functions of genes related to salt gland development and salt tolerance. In this study, an R1-type MYB transcription factor gene was screened from L. bicolor, named LbMYB48, and its expression was strongly induced by salt stress. Subcellular localization analysis showed that LbMYB48 was localized in the nucleus. LbMYB48 protein has transcriptional activation activity shown by transcriptional activation experiments. The density of salt glands in the leaves and the salt secretion capacity of LbMYB48-silenced lines were decremented, as demonstrated by the leaf disc method to detect sodium ion secretion. Furthermore, salt stress index experiments revealed that the ability of LbMYB48-silenced lines to resist salt stress was significantly reduced. LbMYB48 regulates salt gland development and salt tolerance in L. bicolor mainly by regulating the expression of epidermal cell development related genes such as LbCPC-like and LbDIS3 and salt stress-related genes (LbSOSs, LbRLKs, and LbGSTs) as demonstrated by RNA-seq analysis of LbMYB48-silenced lines. The heterologous over-expression of LbMYB48 in Arabidopsis thaliana improves salt tolerance of plants by stabilizing ion and osmotic balance and is likely to be involved in the abscisic acid signaling pathway. Therefore, LbMYB48, a transcriptional activator regulates the salt gland development of L. bicolor and salt tolerance of L. bicolor and A. thaliana.

Effects of Fertilization Approaches on Plant Development and Fertilizer Use of Citrus

Fertilization is an important part of citrus crop management. However, limited details are available about the fertilization approach on citrus plant development. A pot experiment for the fertilization approaches and fertigation levels were conducted in this study. Four fertilization approaches, namely, drip fertigation (DF), broadcast fertilization (CK+), hole fertilization (HF) and pour fertilization (PF) were tested. The fertigation level treatment included 100% (DF-337.5), 80% (DF-270), 60% (DF-202.5) and 40% (DF-135) fertilizer supply with DF, and the 100% fertilizer supply with broadcast fertilization were served as control (CK). The results showed that DF not only increased the absorptions of nitrogen (N), phosphorus (P) and potassium (K) but also promoted citrus plant height, stem diameter and dry weight. In fruit quality, DF had the highest fruit total soluble solid (TSS) and titratable acidity (TA) contents. For fertilizer loss, DF had the lowest N and K leaching losses of 9.26% and 4.05%, respectively, and the lowest N and K runoff losses among the approaches. Isotopic tracing with 15N indicated that DF had the highest fertilizer use efficiency. Based on the analysis of fertigation levels, DF approach with 60% fertilizer reduction could improve citrus plant development. Therefore, DF promoted citrus plant growth and fruit quality by accelerating fertilizer utilization and impairing fertilizer loss. The fertilizer amount in citrus production could be reduced significantly using DF.

Hydrogeochemical processes controlling the salinity of surface water and groundwater in an inland saline-alkali wetland in western Jilin, China

Understanding the hydrochemical evolutionary mechanisms of surface water and groundwater in saline-alkali wetlands in arid and semi-arid regions is necessary for assessing how wetland water resource utilization and restoration processes may affect the natural interface between wetland salinity and water. The Momoge National Nature Reserve (MNNR) is an inland wetland in northeastern China that is mainly fed by irrigation water and floods from the Nenjiang River. The purpose of the present study is to describe the spatial distribution characteristics of surface water and groundwater hydrochemistry and salinity in the MNNR and analyze the main processes controlling these parameters. The composition of stable isotopes (δ2H and δ18O) and water chemistry, including the levels of Na, K, Ca, Mg, HCO3, SO4, and Cl, of 156 water samples were analyzed. The results show that the lake water in the MNNR is at a risk of salinization owing to a high degree of evaporation. The analysis of the ion ratio and mineral saturation index showed that the ions in water are primarily derived from aquifer leaching, and the precipitation of Ca2+ and Mg2+ resulted in lower Ca2+ and Mg2+ levels in lake water than in groundwater. Hydrogen and oxygen stable isotope and deuterium excess analyses show that evaporation is the dominant factor controlling the hydrochemistry and salinity of lake water in the MNNR. Long-term effective monitoring of lake water and groundwater must be developed to provide an early warning for the salinization of lake water and a scientific basis for the protection and restoration of wetland ecosystem functions within the MNNR.

Foliarly Applied 24-Epibrassinolide Modulates the Electrical Conductivity of the Saturated Rhizospheric Soil Extracts of Soybean under Salinity Stress

The accumulation of salts within the rhizosphere is a common phenomenon in arid and semi-arid regions where irrigation water is high in salts. A previous study established the ameliorative effect of foliarly applied 24-epibrassinolide (BR) on soybean under salinity stress. As a follow-up to that study, this work evaluated the effects of BR on the electrical conductivity of saturated soil extracts (EC_ses) under soybean exposed to salt stress. Three salinity levels (3.24, 6.06 and 8.63 dS/m) in a factorial combination with six frequencies of BR application—control, seedling, flowering, podding, seedling + flowering and seedling + flowering + podding—were the treatments, and the rhizospheric EC_se was monitored from 3 to 10 weeks after the commencement of irrigation with saline water (WAST). The principal component analysis revealed that samples in saline BR treatments clustered together based on the BR application frequencies. There was a significant increase in EC_se with increases in salinity and WAST. The frequent application of BR significantly reduced EC_se to 5.07 and 4.83 dS/m relative to the control with 6.91 dS/m, respectively, at week 10. At 8.63 dS/m, the application of BR (seedling + flowering + podding) reduced EC_se by 31.96% compared with the control. The underlining mechanism is a subject for further investigation.

Biogeographical Patterns and Assembly of Bacterial Communities in Saline Soils of Northeast China

Increasing salinity undermines soil fertility and imposes great threats to soil ecosystem productivity and ecological sustainability. Microbes with the ability to adapt to environmental adversity have gained increasing attention for maintenance and restoration of the salt-affected soil ecosystem structure and functioning; however, the characterization of microbial communities in saline–sodic soils remains limited. This study characterized the bacterial community composition and diversity in saline–sodic soils along a latitude gradient across Northeast China, aiming to reveal the mechanism of physicochemical and geographic characteristics shaping the soil bacterial communities. Our results showed that the bacterial community composition and diversity were significantly impacted by soil pH, electrical conductivity, Na⁺, K⁺, Cl⁻, and CO₃²⁻. Significant differences in bacterial diversity were revealed along the latitude gradient, and the soil factors accounted for 58.58% of the total variations in bacterial community composition. Proteobacteria, Actinobacteria, Gemmatimonadetes, Chloroflexi, and Bacteroidetes were dominant across all samples. Actinobacteria and Gemmatimonadetes were significantly enriched in high soil sodicity and salinity, while Acidobacteria and Proteobacteria were suppressed by high pH and salt stress in the saline–sodic soils. Increase in soil pH and salinity significantly decreased bacterial species richness and diversity. Community composition analysis indicated that bacterial taxonomic groups (e.g., Bacillus, Egicoccus, Truepera, Halomonas, and Nitrolancea) that may adapt well to high salinity were greatly enriched in the examined soils. The findings collectively evidenced that bacterial community composition and diversity in a broad biographic scale were determined by niche-based environmental characteristics and biotic interactions. The profiling of the soil bacterial communities along the latitude gradient will also provide a basis for a better understanding of the salt-affected soil ecosystem functioning and restoration of these soil ecosystems.

Bacillus halotolerans KKD1 induces physiological, metabolic and molecular reprogramming in wheat under saline condition

Salt stress decreases plant growth and is a major threat to crop yields worldwide. The present study aimed to alleviate salt stress in plants by inoculation with halophilic plant growth-promoting rhizobacteria (PGPR) isolated from an extreme environment in the Qinghai-Tibetan Plateau. Wheat plants inoculated with Bacillus halotolerans KKD1 showed increased seedling morphological parameters and physiological indexes. The expression of wheat genes directly involved in plant growth was upregulated in the presence of KKD1, as shown by real-time quantitative PCR (RT-qPCR) analysis. The metabolism of phytohormones, such as 6-benzylaminopurine and gibberellic acid were also enhanced. Mining of the KKD1 genome corroborated its potential plant growth promotion (PGP) and biocontrol properties. Moreover, KKD1 was able to support plant growth under salt stress by inducing a stress response in wheat by modulating phytohormone levels, regulating lipid peroxidation, accumulating betaine, and excluding Na⁺. In addition, KKD1 positively affected the soil nitrogen content, soil phosphorus content and soil pH. Our findings indicated that KKD1 is a promising candidate for encouraging wheat plant growth under saline conditions.

Ion absorption, distribution and salt tolerance threshold of three willow species under salt stress

To investigate the response mechanism and salt tolerance threshold of three willow seedlings (Salix matsudana, Salix gordejevii, Salix linearistipularis), the absorption, transport and distribution of salt ions (Na⁺, K⁺, Ca²⁺) were studied under hydroponic conditions with different salt concentrations (CK, 171, 342, 513, and 684 mm) and treatment times (1, 3, 5, 8, 11, and 15 days). Salix linearistipularis has the weakest ability to maintain its apparent shape, while Salix matsudana has the strongest ability. The three plants have a certain Na⁺ interception ability, and the interception abilities of Salix matsudana and Salix gordejevii are higher than that of Salix linearistipularis. The leaf S _AK,Na of Salix linearistipularis were higher than those of Salix matsudana and Salix gordejevii. The leaf selection ability was the highest, and the selection ability of the root system was the lowest in Salix linearistipularis. The long-term low salt concentration and the short-term high salt concentration can increase the root and leaf salinity. Salix matsudana grows more stably in a long-term high-salt stress environment, and Salix gordejevii grows stably in a short-term high-salt stress environment. However, Salix linearistipularis is more suitable for planting as an indicative plant because of its sensitivity to salt stress. The root Na⁺ content of Salix matsudana and Salix gordejevii was 34.21 mg/g, which was the maximum root retention capacity. Once the accumulation of Na⁺ content in roots exceeds this value, the rejection capacity of roots is broken through, and the selective ion absorption capacity will rapidly become weak, which easily leads to the death of plants.

Biochar Additions Alter the Abundance of P-Cycling-Related Bacteria in the Rhizosphere Soil of Portulaca oleracea L. under Salt Stress

Numerous reports confirm a positive impact of biochar amendments on soil enzyme activities, nutrient cycles, and, finally, plant growth and development. However, reports explaining the process behind such diverse observations are scarce. The aim of the present study was (1) to evaluate the effect of biochar on the growth of purslane (Portulaca oleracea L.) and nutrients; (2) to determine the response of rhizosphere enzyme activities linked to soil phosphorus cycling after bio-char amendment under non–saline and saline soil conditions. Furthermore, we investigate whether adding biochar to soil alters the abundance of P-cycling-related bacteria. Two rates of biochar (2% and 4%) were applied in pot experiments. Biochar addition of 2% significantly increased plant growth under non-saline and saline soil conditions by 21% and 40%, respectively. Moreover, applying biochar increased soil microbial activity as observed by fluorescein diacetate (FDA) hydrolase activity, as well as phosphomonoesterase activities, and the numbers of colony-forming units (CFU) of P-mobilizing bacteria. Soil amended with 2% biochar concentration increased total soil nitrogen (Nt), phosphorus (P), and total carbon (Ct) concentrations by 18%, 15%, and 90% under non-saline soil conditions and by 29%, 16%, and 90% in saline soil compared the control, respectively. The soil FDA hydrolytic activity and phosphatase strongly correlate with soil Ct, Nt, and P contents. The rhizosphere soil collected after biochar amendment showed a higher abundance of tricalcium phosphate-solubilizing bacteria than the control soil without biochar. Overall, this study demonstrated that 2% maize-derived biochar positively affects halophyte plant growth and thus could be considered for potential use in the reclamation of degraded saline soil.

Structural determinants of phytoremediation capacity in saltmarsh halophyte Diplachne fusca (L.) P. Beauv. ex Roem. & Schult. subsp. fusca

Micro and macro-morphological features contribute to plants' tolerance to a variety of environmental pollutants. The contribution of such structural modifications in the phytoremediation potential of Diplachne fusca populations collected from five saline habitats were explored when treated with 100 to 400 mM NaCl for 75 days along with control. Structural modifications in the populations from the highest salinity included development of aerenchyma in stem instead of chlorenchyma, absence of excretory hairs in stem, and exceptionally large trichomes on the leaf surface to help excretion of excess salt. Large parenchyma cells provided more space for water and solute storage, while broad metaxylem vessels were linked to better conduction water and nutrients, which ultimately excreted via glandular hairs, microhairs, and vesicular hairs. Broad metaxylem vessels and exceptionally long hairs observed in the populations collected from 52 dS m^-1. In conclusion, large stem aerenchyma, exceptionally large trichomes on the leaf surface, and tightly packed outer cortical region in roots with intensive sclerification just inside the epidermis accompanied with salt excretion via glandular hairs, microhairs, and vesicular hairs were the main anatomical modifications involved in the phytoremediation potential of D. fusca in hyper-saline environments.

CeO2 nanoparticles improved cucumber salt tolerance is associated with its induced early stimulation on antioxidant system

Salinity is a global issue limiting efficient agricultural production. Nano-enabled plant salt tolerance is a hot topic. However, the role of nanoparticles induced possible early stimulation on antioxidant system in its improved plant salt tolerance is still largely unknown. Here, poly (acrylic) acid coated nanoceria (cerium oxide nanoparticles) (PNC, 7.8 nm, -31 mV) with potent ROS (reactive oxygen species) scavenging ability are used. Compared with control, no significant difference of H₂O₂ and O₂^•─ content, MDA (malondialdehyde) content, relative electric conductivity, and Fv/Fm was found in leaves and/or roots of cucumber before onset of salinity stress, regardless of leaf or root application of PNC. While, before onset of salinity stress, compared with control, the activities of SOD (superoxide dismutase, up to 1.8 folds change), POD (peroxidase, up to 2.5 folds change) and CAT (catalase, up to 2.3 folds change), and the content of GSH (glutathione, up to 3.0 folds change) and ASA (ascorbic acid, up to 2.4 folds change) in leaves and roots of cucumber with PNC leaf spray or root application were significantly increased. RNA seq analysis further confirmed that PNC foliar spray upregulates more genes in leaves over roots than the root application. These results showed that foliar sprayed PNC have stronger early stimulation effect on antioxidant system than the root applied one and leaf are more sensitive to PNC stimulation than root. After salt stress, cucumber plants with foliar sprayed PNC showed better improvement in salt tolerance than the root applied one. Also, plants with foliar sprayed PNC showed significant higher whole plant cerium content than the root applied one after salt stress. In summary, we showed that foliar spray of nanoceria is more optimal than root application in terms of improving cucumber salt tolerance, and this improvement is associated with better stimulation on antioxidant system in plants.

Biochemical, transcriptomic, gut microbiome responses and defense mechanisms of the earthworm Eisenia fetida to salt stress

The accumulation of sodium chloride (NaCl) in soil is a worldwide problem with detrimental effects on the survival of soil animals. The effects of NaCl on earthworms remain unclear. Here, we show that the growth rate, cocoon production rate, annetocin precursor (ANN) mRNA level, and superoxide dismutase and catalase activities in earthworms were reduced under NaCl stress, whereas the mortality rate, reactive oxygen species (ROS) and malondialdehyde activity level increased. Histological damage to the earthworm body wall and intestine were observed under NaCl stress. NaCl stress increased DNA damage in the seminal vesicle and coelomocytes. The mRNA level of lumbrokinase, 1,3-beta-glucanse, coelomic cytolytic factor (CCF1), and alpha-amylase was significantly down-regulated, whereas that of earthworm excitatory peptides2 (EEP2) was up-regulated. From 16 S rRNA sequencing, the earthworm gut microbiota diversity decreased under NaCl stress. However, Verminephrobacter, Kluyvera, Lactobacillus, and Ochrobactrum increased under NaCl stress. These findings contribute to the risk assessment of the salt stress on soil organisms.

Charge balance calculations for mixed salt systems applied to a large dataset from the built environment

Understanding salt mixtures in the built environment is crucial to evaluate damage phenomena. This contribution presents charge balance calculations applied to a dataset of 11412 samples taken from 338 sites, building materials showing signs of salt deterioration. Each sample includes ion concentrations of Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl^-, NO₃^-, and SO₄^2- adjusted to reach charge balance for data evaluation. The calculation procedure follows two distinct pathways: i) an equal adjustment of all ions, ii) adjustments to the cations in sequence related to the solubility of the theoretical solids. The procedure applied to the dataset illustrates the quantification of salt mixture compositions and highlights the extent of adjustments applied in relation to the sample mass to aid interpretation. The data analysis allows the identification of theoretical carbonates that could influence the mixture behavior. Applying the charge balance calculations to the dataset validated common ions found in the built environment and the identification of three typical mixture compositions. Additionally, the data can be used as direct input for thermodynamic modeling.

Lb1G04202, an Uncharacterized Protein from Recretohalophyte Limonium bicolor, Is Important in Salt Tolerance

With global increases in saline soil, it has become increasingly important to decipher salt-tolerance mechanisms and identify strategies to improve salt tolerance in crops. Halophytes complete their life cycles in environments containing ≥200 mM NaCl; these remarkable plants provide a potential source of genes for improving crop salt tolerance. Recretohalophytes such as Limonium bicolor have salt glands that secrete Na⁺ on their leaf epidermis. Here, we identified Lb1G04202, an uncharacterized gene with no conserved domains, from L. bicolor, which was highly expressed after NaCl treatment. We confirmed its expression in the salt gland by in situ hybridization, and then heterologously expressed Lb1G04202 in Arabidopsis thaliana. The transgenic lines had a higher germination rate, greater cotyledon growth percentage, and longer roots than the wild type (WT) under NaCl treatments (50, 100 and 150 mM). At the seedling stage, the transgenic lines grew better than the WT and had lower Na⁺ and malonyldialdehyde accumulation, and higher K⁺ and proline contents. This corresponded with the high expression of the key proline biosynthesis genes AtP5CS1 and AtP5CS2 under NaCl treatment. Isotonic mannitol treatment showed that Lb1G04202 overexpression significantly relieved osmotic stress. Therefore, this novel gene provides a potential target for improving salt tolerance.

Changes in Intraspecific Diversity of the Arbuscular Mycorrhizal Community Involved in Plant-Plant Interactions Between Sporobolus robustus Kunth and Prosopis juliflora (Swartz) DC Along an Environmental Gradient

The intensification of biological processes coping with salt stress became a major issue to mitigate land degradation. The Sine-Saloum Delta in Senegal is characterized by salt-affected soils with vegetation dominated by salt-tolerant grass Sporobolus robustus and shrubs like Prosopis juliflora. Plant experiments in controlled conditions suggested that arbuscular mycorrhizal (AM) fungi might be the key actors of facilitation process observed between S. robustus and P. juliflora, but the AM fungal community determinants are largely unknown. The current field-based study aimed at (1) characterizing the environmental drivers (rhizosphere physico-chemical properties, plant type and season) of the AM fungal community along an environmental gradient and (2) identifying the AM fungal taxa that might explain the S. robustus-mediated benefits to P. juliflora. Glomeraceae predominated in the two plants, but a higher richness was observed for S. robustus. The pH and salinity were the main drivers of AM fungal community associated with the two plants, negatively impacting richness and diversity. However, while a negative impact was also observed on mycorrhizal colonization for S. robustus, P. juliflora showed opposite colonization patterns. Furthermore, no change was observed in terms of AM fungal community dissimilarity between the two plants along the environmental gradient as would be expected according to the stress-gradient and complementary hypotheses when a facilitation process occurs. However, changes in intraspecific diversity of shared AM fungal community between the two plants were observed, highlighting 23 AM fungal OTUs associated with both plants and the highest salinity levels. Consequently, the increase of their abundance and frequency along the environmental gradient might suggest their potential role in the facilitation process that can take place between the two plants. Their use in ecological engineering could also represent promising avenues for improving vegetation restoration in saline Senegalese's lands.

Chloride accumulation in aboveground biomass of three macrophytes (Phragmites australis, Juncus maritimus, and Typha latifolia) depending on their growth stages and salinity exposure: application for Cl- removal and phytodesalinization

Anthropogenic activities can be the source of saline solid wastes that need to be treated to reduce their salt load to meet the purposes of reuse, valorization or storage. In this context, chloride remediation can be achieved using high-salt accumulating plants. However, there is very limited information on the comparative potential of different species in the same environment, and only scarce data concerning their efficiency as a function of growth stage. In order to rationalize these selection criteria, three macrophytes i.e., common reed (Phragmites australis), sea rush (Juncus maritimus), and cattail (Typha latifolia), were cultivated at two growth stages (6-months old and 1-year old) for 65 days in Cl^- spiked substrates (from 0 up to 24 ‰ NaCl). The plants' survival and potential capacity for removal of Cl^- from substrates and accumulation in shoots were investigated. For the three studied species, mature and juvenile plants display a high tolerance to salinity. However, mature specimens with higher shoot biomass and Cl^- contents are capable of greater chloride removal than juvenile plants. The sole exception is P. australis which displays just the same phytoremediation potential for both mature and juvenile specimens. Moreover, P. australis has the lowest potential when compared with other species, being 1.5 and 3 times lower than for J. maritimus and T. latifolia. When considering the plant growth and the shoot biomass production, chloride removal rates from the substrate point that mature J. maritimus should preferentially be used to design an operational chloride remediation system. The results highlight the relevance of considering the growth stage of plants used for Cl^- removal. HIGHLIGHTS: 1) Mature and juvenile specimens of J. maritimus, P. australis, and T. latifolia have high salinity tolerance in solid media spiked up to 24 ‰ NaCl. 2) Mature plants have generally better Cl^- removal and phytoremediation performances than juvenile specimens. 3) J. maritimus is the most effective species for chloride phytoremediation with high survival and high Cl^- sequestration in shoots. 4) T. latifolia has high Cl^- removal in shoots and good remediation capacities but also shows sign of stress. 5) P. australis shows low Cl^- sequestration and is a poor candidate for chloride remediation from substrate.

Monitoring soil salinization and its spatiotemporal variation at different depths across the Yellow River Delta based on remote sensing data with multi-parameter optimization

Soil salinization is recognized as a key issue negatively affecting agricultural productivity and wetland ecology. It is necessary to develop effective methods for monitoring the spatiotemporal distribution of soil salinity at a regional scale. In this study, we proposed an optimized remote sensing-based model for detecting soil salinity in different depths across the Yellow River Delta (YRD), China. A multi-dimensional model was built for mapping soil salinity, in which five types of predictive factors derived from Landsat satellite images were exacted and tested, 94 in-situ measured soil salinity samples with depths of 30-40 cm and 90-100 cm were collected to establish and validate the predicting model result. By comparing multiple linear regression (MLR) and partial least squares regression (PLSR) models with considering the correlation between predictive factors and soil salinity, we established the optimized prediction model which integrated the multi-parameter (including SWIR1, SI9, MSAVI, Albedo, and SDI) optimization approach to detect soil salinization in the YRD from 2003 to 2018. The results indicated that the estimates of soil salinity by the optimized prediction model were in good agreement with the measured soil salinity. The accuracy of the PLSR model performed better than that of the MLR model, with the R² of 0.642, RMSE of 0.283, and MAE of 0.213 at 30-40 cm depth, and with the R² of 0.450, RMSE of 0.276, and MAE of 0.220 at 90-100 cm depth. From 2003 to 2018, the soil salinity showed a distinct spatial heterogeneity. The soil salinization level of the coastal shoreline was higher; in contrast, lower soil salinization level occurred in the central YRD. In the last 15 years, the soil salinity at depth of 30-40 cm experienced a decreased trend of fluctuating, while the soil salinity at depth of 90-100 cm showed fluctuating increasing trend.

Treatment wetlands and phyto-technologies for remediation of winery effluent: Challenges and opportunities

The composition and concentration of contaminants present in winery wastewater fluctuate through space and time, presenting a challenge for traditional remediation methods. Bio-hydrogeochemical engineered systems, such as treatment wetlands, have been demonstrated to effectively reduce contaminant loads prior to disposal or reuse of the effluent. This review identifies and details the status quo and challenges associated with (i) the characteristics of winery wastewater, and the (ii) functional components, (iii) operational parameters, and (iv) performance of treatment wetlands for remediation of winery effluent. Potential solutions to challenges associated with these aspects are presented, based on the latest literature. A particular emphasis has been placed on the phytoremediation of winery wastewater, and the rationale for selection of plant species for niche bioremediatory roles. This is attributed to previously reported low-to-negative removal percentages of persistent contaminants, such as salts and heavy metals that may be present in winery wastewater. A case for the inclusion of selected terrestrial halophytes in treatment wetlands and in areas irrigated using winery effluent is discussed. These are plant species that have an elevated ability to accumulate, cross-tolerate and potentially remove a range of persistent contaminants from winery effluent via various phytotechnologies (e.g., phytodesalination).