Global predictions of primary soil salinization under changing climate in the 21st century

High-elevation-induced decrease in soil pH weakens ecosystem multifunctionality by influencing soil microbiomes

Plant environmental stress response has become a global research hotspot, yet there is a lack of clear understanding regarding the mechanisms that maintain microbial diversity and their ecosystem services under environmental stress. In our research, we examined the effects of moderate elevation on the rhizosphere soil characteristics, microbial community composition, and ecosystem multifunctionality (EMF) within agricultural systems. Our findings revealed a notable negative correlation between EMF and elevation, indicating a decline in multifunctionality at higher elevations. Additionally, our analysis across bacterial and protistan communities showed a general decrease in microbial richness with increasing elevation. Using random forest models, pH was identified as the key environmental stressor influencing microbial communities. Furthermore, we found that microbial community diversity is negatively correlated with stability by mediating complexity. Interestingly, while pH was found to affect the complexity within bacterial networks, it did not significantly impact the ecosystem stability along the elevation gradients. Using a Binary-State Speciation and Extinction (BiSSE) model to explore the evolutionary dynamics, we found that Generalists had higher speciation rates and lower extinction rates compared to specialists, resulting in a skewed distribution towards higher net diversification for generalists under increasing environmental stress. Moreover, structural equation modeling (SEM) analysis highlighted a negative correlation between environmental stress and community diversity, but showed a positive correlation between environmental stress and degree of cooperation & competition. These interactions under environmental stress indirectly increased community stability and decreased multifunctionality. Our comprehensive study offers valuable insights into the intricate relationship among environmental factors, microbial communities, and ecosystem functions, especially in the context of varying elevation gradients. These findings contribute significantly to our understanding of how environmental stressors affect microbial diversity and ecosystem services, providing a foundation for future ecological research and management strategies in similar contexts.

SOS2-AFP2 module regulates seed germination by inducing ABI5 degradation in response to salt stress in Arabidopsis

Soil salinity pose a significant challenge to global agriculture, threatening crop yields and food security. Understanding the salt tolerance mechanisms of plants is crucial for improving their survival under salt stress. AFP2, a negative regulator of ABA signaling, has been shown to play a crucial role in salt stress tolerance during seed germination. Mutations in AFP2 gene lead to increased sensitivity to salt stress. However, the underline mechanisms by which AFP2 regulates seed germination under salt stress remain elusive. In this study, we identified a protein interaction between AFP2 and SOS2, a Ser/Thr protein kinase known to play a critical role in salt stress response. Using a combination of genetic, biochemical, and physiological approaches, we investigated the role of the SOS2-AFP2 module in regulating seed germination under salt stress. Our findings reveal that SOS2 physically interacts with AFP2 and stabilizes it, leading to the degradation of the ABI5 protein, a negative transcription factor in seed germination under salt stress. This study sheds light on previously unknown connections within salt stress and ABA signaling, paving the way for novel strategies to enhance plant resilience against environmental challenges.

The Spartina alterniflora genome sequence provides insights into the salt-tolerance mechanisms of exo-recretohalophytes

Spartina alterniflora is an exo-recretohalophyte Poaceae species that is able to grow well in seashore, but the genomic basis underlying its adaptation to salt tolerance remains unknown. Here, we report a high-quality, chromosome-level genome assembly of S. alterniflora constructed through PacBio HiFi sequencing, combined with high-throughput chromosome conformation capture (Hi-C) technology and Illumina-based transcriptomic analyses. The final 1.58 Gb genome assembly has a contig N50 size of 46.74 Mb. Phylogenetic analysis suggests that S. alterniflora diverged from Zoysia japonica approximately 21.72 million years ago (MYA). Moreover, whole-genome duplication (WGD) events in S. alterniflora appear to have expanded gene families and transcription factors relevant to salt tolerance and adaptation to saline environments. Comparative genomics analyses identified numerous species-specific genes, significantly expanded genes and positively selected genes that are enriched for 'ion transport' and 'response to salt stress'. RNA-seq analysis identified several ion transporter genes including the high-affinity K+ transporters (HKTs), SaHKT1;2, SaHKT1;3 and SaHKT1;8, and high copy number of Salt Overly Sensitive (SOS) up-regulated under high salt conditions, and the overexpression of SaHKT2;4 in Arabidopsis thaliana conferred salt tolerance to the plant, suggesting specialized roles for S. alterniflora to adapt to saline environments. Integrated metabolomics and transcriptomics analyses revealed that salt stress activate glutathione metabolism, with differential expressions of several genes such as γ-ECS, GSH-S, GPX, GST and PCS in the glutathione metabolism. This study suggests several adaptive mechanisms that could contribute our understanding of evolutional basis of the halophyte.

Multi-omics integrative analysis provided new insights into alkaline stress in alfalfa

Saline-alkali stress is one of the main abiotic stresses that limits plant growth. Salt stress has been widely studied, but alkaline salt degradation caused by NaHCO3 has rarely been investigated. In the present study, the alfalfa cultivar 'Zhongmu No. 1' was treated with 50 mM NaHCO3 (0, 4, 8, 12 and 24 h) to study the resulting enzyme activity and changes in mRNA, miRNA and metabolites in the roots. The results showed that the enzyme activity changed significantly after alkali stress treatment. The genomic analysis revealed 14,970 differentially expressed mRNAs (DEMs), 53 differentially expressed miRNAs (DEMis), and 463 differentially accumulated metabolites (DAMs). Combined analysis of DEMs and DEMis revealed that 21 DEMis negatively regulated 42 DEMs. In addition, when combined with Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of DEMs and DAMs, we found that phenylpropanoid biosynthesis, flavonoid biosynthesis, starch and sucrose metabolism and plant hormone signal transduction played important roles in the alkali stress response. The results of this study further elucidated the regulatory mechanism underlying the plant response to alkali stress and provided valuable information for the breeding of new saline-alkaline tolerance plant varieties.

Precipitation changes alter plant dominant species and functional groups by changing soil salinity in a coastal salt marsh

Specific mechanisms of precipitation change due to global climate variability on plant communities in coastal salt marsh ecosystems remain unknown. Hence, a field manipulative precipitation experiment was established in 2014 and 5 years of field surveys of vegetation from 2017 to 2021 to explore the effects of precipitation changes on plant community composition. The results showed that changes in plant community composition were driven by dominant species, and that the dominance of key species changed significantly with precipitation gradient and time, and that these changes ultimately altered plant community traits (i.e., community density, height, and species richness). Community height increased but community density decreased with more precipitation averaged five years. Furthermore, changes in precipitation altered dominant species composition and functional groups mainly by influencing soil salinity. Salinity stress caused by decreased precipitation shifted species composition from a dominance of taller perennials and grasses to dwarf annuals and forbs, while the species richness decreased. Conversely, soil desalination caused by increased precipitation increased species richness, especially increasing in the dominance of grasses and perennials. Specifically, Apocynaceae became dominance from rare while Amaranthaceae decreased in response to increased precipitation, but Poaceae was always in a position of dominance. Meanwhile, the dominance of grasses and perennials has the cumulative effect of years and their proportion increased under the increased 60% of ambient precipitation throughout the years. However, the annual forb Suaeda glauca was gradually losing its dominance or even becoming extinct over years. Our study highlights that the differences in plant salinity tolerance are key to the effects of precipitation changes on plant communities in coastal salt marsh. These findings aim to provide a theoretical basis for predicting vegetation dynamics and developing ecological management strategies to adapt to future precipitation changes.

Characterisation of a major QTL for sodium accumulation in tomato grown in high salinity

Soil salinity is a serious concern for tomato culture, affecting both yield and quality parameters. Although some genes involved in tomato salt tolerance have been identified, their genetic diversity has been rarely studied. In the present study, we assessed salt tolerance-related traits at juvenile and adult stages in a large core collection and identified salt tolerance quantitative trait loci (QTLs) by genome-wide association study (GWAS). The results suggested that a major QTL is involved in leaf sodium accumulation at both physiological stages. We were able to identify the underlying candidate gene, coding for a well-known sodium transporter, called SlHKT1.2. We showed that an eQTL for the expression of this gene in roots colocalized with the above ground sodium content QTL. A polymorphism putatively responsible for its variation was identified in the gene promoter. Finally, to extend the applicability of these results, we carried out the same analysis on a test-cross panel composed of the core collection crossed with a distant line. The results indicated that the identified QTL retained its functional impact even in a hybrid genetic context: this paves the way for its use in breeding programs aimed at improving salinity tolerance in tomato cultivars.

Trend of soil salinization in Africa and implications for agro-chemical use in semi-arid croplands

Soil salinization is a gradual degradation process that begins as a minor problem and grows to become a significant economic loss if no control action is taken. It progressively alters the soil environment which eventually negatively affects plants and organism that were not originally adapted for saline conditions. Soil salinization arises from diverse sources such as side-effects of long-term use of agro-chemicals, saline parent rocks, periodic inundation of soil with saline water, etc. In Africa, soil salinization has not been adequately documented particularly in the croplands. The objective of this study was to identify trends of cropland salinization in Africa and how its relationship with long-term land use practices affected the soil environment. The study analysed soil salinization between 1965 and 2020 using measured electrical conductivity (EC), spatial modelling with environmental covariates, and national statistics on cropland expansion and application of mineral fertilizers, herbicides, and pesticides. The results showed increasing trends of EC in Africa due to climatic and land use drivers. Increasing trends of EC, which evidenced salinization, was found in 31 million hectares of topsoils and 18 million hectares of subsoils. About 2 million hectares of croplands were depicted with salinization and >25 million hectares at the risk of salinization in the arid and semi-arid areas. The study also found statistical relationships between semi-arid cropland salinization and trends of agro-chemical use and cropland sizes. There were significant (p < 0.001) positive correlations between semi-arid cropland salinization and trends of cropland expansion and applied nitrogenous fertilizers. It found that increasing trend of applied mineral nitrogenous fertilizers could double the odds of salinization in semi-arid croplands while cropland expansion could increase the odds of semi-arid cropland salinization by >10 %. These findings present ground-breaking baseline information for future works on sustainable land-use practices that can control cropland soil salinization in Africa.

Soil pH amendment alters the abundance, diversity, and composition of microbial communities in two contrasting agricultural soils

Soil microorganisms are the most active participants in terrestrial ecosystems, and have key roles in biogeochemical cycles and ecosystem functions. Despite the extensive research on soil pH as a key predictor of microbial community and composition, a limitation of these studies lies in determining whether bacterial and/or fungal communities are directly or indirectly influenced by pH. We conducted a controlled laboratory experiment to investigate the effects of soil pH amendment (+/- 1-2 units) with six levels on soil microbial communities in two contrasting Chinese agricultural soils (pH 8.43 in Dezhou, located in the North China Plain, Shandong vs pH 6.17 in Wuxi, located in the Taihu Lake region, Jiangsu, east China). Results showed that the fungal diversity and composition were related to soil pH, but the effects were much lower than the effects of soil pH on bacterial community in two soils. The diversity and composition of bacterial communities were more closely associated with soil pH in Wuxi soils compared to Dezhou soils. The alpha diversity of bacterial communities peaked near in situ pH levels in both soils, displaying a quadratic fitting pattern. Redundancy analysis and variation partition analysis indicated that soil pH affected bacterial community and composition by directly imposing a physiological constraint on soil bacteria and indirectly altering soil characteristics (e.g., nutrient availability). The study also examined complete curves of taxa relative abundances at the phylum and family levels in response to soil pH, with most relationships conforming to a quadratic fitting pattern, indicating soil pH is a reliable predictor. Furthermore, soil pH amendment affected the transformation of nitrogen and the abundances of functional genes involved in the nitrogen cycle, and methane production and consumption. Overall, results from this study would enhance our comprehension of how soil microorganisms in contrasting farmlands will respond to soil pH changes, and would contribute to more effective soil management and conservation strategies.

IMPORTANCE

This study delves into the impact of soil pH on microbial communities, investigating whether pH directly or indirectly influences bacterial and fungal communities. The research involved two contrasting soils subjected to a 1-2 pH unit amendment. Results indicate bacterial community composition was shaped by soil pH through physiological constraints and nutrient limitations. We found that most taxa relative abundances at the phylum and family levels responded to pH with a quadratic fitting pattern, indicating that soil pH is a reliable predictor. Additionally, soil pH was found to significantly influence the predicted abundance of functional genes involved in the nitrogen cycle as well as in methane production and consumption processes. These insights can contribute to develop more effective soil management and conservation strategies.

The plant disease triangle facing climate change: a molecular perspective

Variations in climate conditions can dramatically affect plant health and the generation of climate-resilient crops is imperative to food security. In addition to directly affecting plants, it is predicted that more severe climate conditions will also result in greater biotic stresses. Recent studies have identified climate-sensitive molecular pathways that can result in plants being more susceptible to infection under unfavorable conditions. Here, we review how expected changes in climate will impact plant-pathogen interactions, with a focus on mechanisms regulating plant immunity and microbial virulence strategies. We highlight the complex interactions between abiotic and biotic stresses with the goal of identifying components and/or pathways that are promising targets for genetic engineering to enhance adaptation and strengthen resilience in dynamically changing environments.

Acetic acid: a cheap but chief metabolic regulator for abiotic stress tolerance in plants

As sessile organisms, plants constantly face a variety of abiotic stresses, such as drought, salinity, and metal/metalloid toxicity, all of which possess significant threats to plant growth and yield potential. Improving plant resilience to such abiotic stresses bears paramount importance in practicing sustainable agriculture worldwide. Acetic acid/acetate has been recognized as an important metabolite with multifaceted roles in regulating plant adaptation to diverse abiotic stresses. Recent studies have elucidated that acetic acid can potentiate plants' inherent mechanisms to withstand the adverse effects of abiotic stresses through the regulation of lipid metabolism, hormone signaling, epigenetic changes, and physiological defense mechanisms. Numerous studies also underpin the potential use of acetic acid in boosting crop production under unfavorable environmental conditions. This review provides a comprehensive update on the understanding of how acetic acid regulates plant photosynthesis, acts as an antitranspirant, detoxifies reactive oxygen species to alleviate oxidative stress, interacts with phytohormones to regulate physiological processes, and improves soil fertility and microbial diversity, with a specific focus on drought, salinity, and metal toxicity. We also highlight the eco-friendly and economic potential of acetic acid that may attract farmers from developing countries to harness the benefits of acetic acid application for boosting abiotic stress resistance in crops. Given that acetic acid is a widely accessible, inexpensive, and eco-friendly compound, the revelation of acetic acid-mediated regulatory pathways and its crosstalk with other signaling molecules will have significant importance in developing a sustainable strategy for mitigating abiotic stresses in crops.

Does the soil microbial community facilitate Mimosa pudica's biological performance under abiotic stress? Growth, tolerance mechanisms, and seismonastic behaviour

Climate change effects such as soil salinisation or drought dramatically affect native and potentially invasive plant species. Mimosa pudica, originally native to South America but spread to Africa and Asia, exhibits great adaptability to disturbed environments in tropical and subtropical areas. It has become a model organism for studying thigmomorphogenetic behaviour due to its ability to display fast responses to mechanical stimuli. We investigated the effects of salt and water stresses on M. pudica in interaction with a Mediterranean coastal dune microbial community by growing plants on soils collected from dunes near Valencia, Spain. Plant biomass, potential mechanisms of stress tolerance, seismonastic response, and phenology were assessed. Abiotic stress, particularly salt stress, adversely affects plant performance and seismonasty. Mimosa pudica, however, displayed the blockage of Na+ transport at the root level as a primary defence mechanism against salinity. When exposed to natural soils, plants produced more leaves and flowers, with lower flower abortion rates than plants in a sterile substrate, and the stimulated plants displayed faster responses across time before reaching a plateau, while the recovery increased with time. Our results highlight the need for integrative and multidisciplinary approaches to understand plant-abiotic stress-microorganisms interactions. In M. pudica, soil microorganisms had weak or no effects on biomass or biochemical stress markers; however, their presence strongly improved reproductive traits and seismonasty, thus facilitating potential plant establishment in a new environment.

A novel exopolysaccharide-producing bacterium, Pseudescherichia liriopis sp. nov. isolated from Liriope platyphylla, enhances the growth of Daucus carota subsp. sativus under drought and salinity stress

Biological and abiotic stresses in plant growth are associated with reduced crop yields. Therefore, improving plant stress resistance can be a crucial strategy to improve crop production. To overcome these problems, plant growth-promoting bacteria are emphasized as one of the alternative tools for sustainable agriculture. This study found a novel strain (L3T) of a plant growth-promoting bacterium in fermented Liriope platyphylla fruit. Strain L3T showed the ability to promote plant growth. The L3T strain promoted plant growth of D. carota subsp. sativus, increasing the length (increase rate compared to the control group, 36.98%), diameter (47.06%), and weight of carrots (81.5%), ultimately increasing the edible area. In addition, we confirmed that plant growth was improved even in situations that inhibited plant growth, such as salinity and drought stress. Strain L3T performed indole production, siderophore production, phosphate solubilization, and nitrogen fixation, all characteristics of a strain that promotes plant growth. Genome analysis revealed genes involved in the growth promotion effects of strain L3T. Additionally, the properties of exopolysaccharides were identified and characterized using FTIR, TGA, and UHPLC. Our results demonstrated that L3 isolated from fermented L. platyphylla fruit can be used to simultaneously alleviate drought and NaCl stress.

Endophytic Fungi for Crops Adaptation to Abiotic Stresses

Endophytic fungi (EFs) have emerged as promising modulators of plant growth and stress tolerance in agricultural ecosystems. This review synthesizes the current knowledge on the role of EFs in enhancing the adaptation of crops to abiotic stress. Abiotic stresses, such as drought, salinity, and extreme temperatures, pose significant challenges to crop productivity worldwide. EFs have shown remarkable potential in alleviating the adverse effects of these stresses. Through various mechanisms, including the synthesis of osmolytes, the production of stress-related enzymes, and the induction of plant defense mechanisms, EFs enhance plant resilience to abiotic stressors. Moreover, EFs promote nutrient uptake and modulate the hormonal balance in plants, further enhancing the stress tolerance of the plants. Recent advancements in molecular techniques have facilitated the identification and characterization of stress-tolerant EF strains, paving the way for their utilization in agricultural practices. Furthermore, the symbiotic relationship between EFs and plants offers ecological benefits, such as improved soil health and a reduced dependence on chemical inputs. However, challenges remain in understanding the complex interactions between EFs and host plants, as well as in scaling up their application in diverse agricultural systems. Future research should focus on elucidating the mechanisms underlying endophytic-fungal-mediated stress tolerance and developing sustainable strategies for harnessing their potential in crop production.

Hydrogen peroxide and salt stress in radish: effects on growth, physiology, and root quality

Hydrogen peroxide (H2O2) plays a central role in responses to salt stress, a major abiotic stress that impacts crop yield worldwide. Despite the evidence that H2O2 mitigates salt stress and improves post-harvest quality on several species, its effects on radish were not investigated so far. Thus, the objective of this study was to evaluate the exogenous application of H2O2 on salt stress mitigation of radish growth, physiology, and post-harvest quality. For this, radish plants were grown in pots for 30 days, being watered with non-saline (0.31 dS m-1) or saline water (120 mM NaCl, 12.25 dS m-1). Plants were leaf-sprayed weekly with water (control - 0 µM H2O2) or H2O2 (150 or 1500 µM) solutions. The experimental design was completely randomized in a 3 × 2 factorial scheme (H2O2 treatments × salt stress conditions). The growth, physiology (gas exchanges, photochemical efficiency, relative water content, electrolyte leakage, and the contents of chlorophylls and carotenoids), and post-harvest attributes of globular roots (color, anthocyanins, vitamin C, phenolic compounds, and soluble solids) were determined. Salt stress decreased gas exchanges and increased electrolyte leakage, which resulted in stunted radish growth, and increased the contents of antioxidants, such as anthocyanins, soluble solids, and vitamin C, improving globular root quality. Conversely, H2O2 did not mitigate salt stress effects on radish growth, photosynthetic capacity, and oxidative damages. Although H2O2 increased vitamin C under non-stressed condition, it was decreased under salt stress. Thus, we conclude that H2O2 did not mitigate salt stress on radish growth and quality.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01476-z.

Biochar and saline soil: mitigation strategy by incapacitating the ecological threats to agricultural land

Soil salinity caused a widespread detrimental issue that hinders productivity in agriculture and ecological sustainability, while waste-derived soil amendments like biochar have drawn attention for their capacity to act as a mitigating agent, by enhancing the physical and chemical features of soil, and contributing to the recovery of agricultural waste resources. However, the information concerning biochar and salinity which affect the physicochemical characteristics of soils, crop physiology, and growth is limited. To investigate whether biochar mitigates the salinity stress on wheat crop seedlings, we grow them with salinity stress (120 mM), and biochar (20 tons ha-1), and its interactive effects. The soil properties of soil organic carbon (SOC), soil organic matter (SOM), dissolved organic carbon (DOC), and soil available phosphorus (SAP) decreased in the saline soil by 36.71%, 46.97%, 26.31%, and 15.00%, while biochar treatment increased SOC, DOC, and SAP contents by 7.42%, 31.57%, and 15.00%, respectively. On the other hand, dissolved organic nitrogen (DON) contents decreased in all the treatments compared to the control. The root growth traits, SPAD values, leaf nitrogen, photosynthetic parameters, antioxidant enzymes, and reactive oxygen species decreased in the saline treatment while increasing in the biochar and interactive treatment. Thus, these activities resulted in higher leaves and root biomass in the biochar treatment alone and interactive treatment of salinity and biochar. According to principal component analysis, redundancy analysis, and the mantel test, using biochar in conjunction with salinity treatment was found to be more effective than salinity treatment alone. The results of this study suggest that biochar can be used as a sustainable agricultural technique and a means of mitigation agent by lowering soil salinity while increasing the biomass of crops.

Silicon: A valuable soil element for improving plant growth and CO2 sequestration

BACKGROUND

Silicon (Si), the second most abundant and quasi-essential soil element, is locked as a recalcitrant silicate mineral in the Earth's crust. The physical abundance of silicates can play an essential role in increasing plant productivity. Plants store Si as biogenic silica (phytoliths), which is mobilized through a chemical weathering process in the soil.

AIM OF REVIEW

Although Si is a critical element for plant growth, there is still a considerable need to understand its dissolution, uptake, and translocation in agroecosystems. Here, we show recent progress in understanding the interactome of Si, CO2, the microbiome, and soil chemistry, which can sustainably govern silicate dissolution and cycling in agriculture.

KEY SCIENTIFIC CONCEPTS OF THIS REVIEW

Si cycling is directly related to carbon cycling, and the resulting climate stability can be enhanced by negative feedback between atmospheric CO2 and the silicate uptake process. Improved Si mobilization in the rhizosphere by the presence of reactive elements (for example, Ca, Na, Al, Zn, and Fe) and Si uptake through genetic transporters in plants are crucial to achieving the dual objectives of (i) enhancing crop productivity and (ii) abiotic stress tolerance. Furthermore, the microbiome is a symbiotic partner of plants. Bacterial and fungal microbiomes can solubilize silicate minerals through intriguingly complex bioweathering mechanisms by producing beneficial metabolites and enzymes. However, the interaction of Si with CO2 and the microbiome's function in mobilization have been understudied. This review shows that enhancing our understanding of Si, CO2, the microbiome, and soil chemistry can help in sustainable crop production during climatic stress events.

Carrabiitol®, a Novel Oligosaccharide Polyol Composition, Mitigates the Impact of Flooding, Drought, Salinity, and High Temperature in Tomato

Abiotic stress results in various physiological and biochemical changes in plants. Osmolytes play a pivotal role in improving the tolerance to abiotic stress in plants. This study evaluated the effectiveness of a commercial formulation, Carrabiitol®, an oligosaccharide polyol composition, in alleviating adverse impacts of abiotic stress in tomato (Solanum lycopersicum L. var. Arka Rakshak) plants. Plants were raised from seed and treated with 1 mL/L, 2 mL/L, and 3 mL/L of Carrabiitol®. The foliage of developing plants was treated at the 2-3 leaf stage (T2, T3, and T4) and at pre-flowering stage (T5, T6, and T7). Growth conditions were compared with those of plants developed from untreated seed (T1). Developing tomato plants were then exposed to flooding, salinity (50 mM NaCl), high temperature (41.1 °C), or drought at the flowering stage. Plants were evaluated for their dry weight, leaf water potential, stomatal conductance, transpiration rate, antioxidant potential, chlorophyll, carotenoid, glucose, sucrose, malondialdehyde, and proline contents. Pre-treated seed, which received a booster treatment at the 2-3 leaf stage (T4 = seed treatment and booster at the 2-3 leaf stage with 3 mL/L Carrabiitol®) and pre-flowering stages (T5, T6, and T7 = seed treatment and booster doses at the pre-flowering stage with 1, 2, and 3 mL/L Carrabiitol®, respectively), was effective in mitigating negative impacts on various growth parameters of stressed tomato plants (p < 0.05). Carrabiitol® may be an effective, sustainable, and bio-rational organic osmolyte formulation for reducing the effects of abiotic stress on plant growth and productivity.

Saline-alkali land reclamation boosts topsoil carbon storage by preferentially accumulating plant-derived carbon

Saline-alkali land is an important cultivated land reserve resource for tackling global climate change and ensuring food security, partly because it can store large amounts of carbon (C). However, it is unclear how saline-alkali land reclamation (converting saline-alkali land into cultivated land) affects soil C storage. We collected 189 adjacent pairs of salt-affected and cultivated soil samples (0-30 cm deep) from the Songnen Plain, eastern coastal area, Hetao Plain, and northwestern arid area in China. Various soil properties, the soil inorganic C (SIC), organic C (SOC), particulate organic C (POC), and mineral-associated organic C (MAOC) densities, and plant- and microbial-derived C accumulation were determined. Saline-alkali land reclamation inconsistently affected the SIC density but significantly (P < 0.001) increased the SOC density. The SOC, POC, and MAOC densities were predicted well by the integrative soil amelioration index. Saline-alkali land reclamation significantly increased plant-derived C accumulation and the plant-derived C to microbial-derived C ratios in all saline-alkali areas, and less microbial transformation of plant-derived C (i.e., less lignin degradation or oxidation) occurred in cultivated soils than salt-affected soils. The results indicated that saline-alkali land reclamation leads to plant-derived C becoming the dominant contributor of SOC storage. POC storage and MAOC storage were strongly linked to plant- and microbial-derived C accumulation, respectively, caused by saline-alkali land reclamation. Our findings suggest that saline-alkali land reclamation increases C storage in topsoil by preferentially promoting plant-derived C accumulation.

Metabolomics analysis reveals enhanced salt tolerance in maize through exogenous Valine-Threonine-Isoleucine-Aspartic acid application

Salt stress is a well-known abiotic constraint that hampers crop productivity, affecting more than 424 million hectares of topsoil worldwide. Applying plant growth regulators externally has proven effective in enhancing crop resilience to salt stress. Previous metabolomics studies revealed an accumulation of Valine-Threonine-Isoleucine-Aspartic acid (VTID) in salt-stressed maize seedlings, suggesting its potential to assist maize adaptation to salt stress. To explore the effectiveness of VTID in enhancing salt tolerance in maize, 10 nM VTID was applied to salt-stressed maize seedlings. The results showed a remarkable 152.29% increase in plant height and a 122.40% increase in fresh weight compared to salt-stressed seedlings. Moreover, the addition of VTID enhanced the activity of antioxidant enzymes, specifically superoxide dismutase (SOD) and catalase (CAT), while reducing the level of malondialdehyde (MDA), a marker of oxidative stress. Additionally, VTID supplementation resulted in a significant increase in osmoregulatory substances such as proline. Metabolomic analysis revealed substantial changes in the metabolite profile of maize seedlings when treated with VTID during salt stress. Differential metabolites (DMs) analysis revealed that the identified DMs primarily belonged to lipids and lipid-like molecules. The receiver operating characteristic curve and linear regression analysis determined a correlation between isodolichantoside and the height of maize seedlings under salt-stress conditions. In conclusion, these findings validate that VTID effectively regulates tolerance in maize seedlings and offers valuable insights into the potential of short peptides for mitigating salt stress.

Wood Distillate Promotes the Tolerance of Lettuce in Extreme Salt Stress Conditions

Soil salinization is an adverse phenomenon in agriculture that severely affects crop growth and yield. The use of natural products, such as wood distillate (WD, derived from the pyrolysis of woody biomass), could be a sustainable approach to enhance the tolerance of plants cultivated in the saline soils. Hence, this study aimed to evaluate the potential of WD, a foliar sprayed at 0.2% (v/v), in lettuce plants subjected to grow under both moderate and high soil sodium chloride (NaCl) concentrations (ranging from 0 to 300 mM). The changes in the physiological and biochemical responses of these plants to the varying salt stress conditions allowed the identification of a maximum tolerance threshold (100 mM NaCl), specific to lettuce. Beyond this threshold, levels related to plant defense antioxidant power (antiradical activity) were lowered, while those indicative of oxidative stress (malondialdehyde content and electrolyte leakage) were raised, causing significant losses in leaf fresh biomass. On the other hand, WD significantly improved plant growth, enabling plants to survive high salt conditions >200 mM NaCl. Collectively, these observations highlight that treatments with WD could be of paramount importance in coping with current environmental challenges to have better yields under soil conditions of high salt concentrations.

Integrated multi-omic approach reveals the effect of a Graminaceae-derived biostimulant and its lighter fraction on salt-stressed lettuce plants

Plant biostimulants are widely applied in agriculture for their ability to improve plant fitness. In the present work, the impact of Graminaceae-derived protein hydrolysate (P) and its lighter molecular fraction F3 (< 1 kDa) on lettuce plants, subjected to either no salt or high salt conditions, was investigated through the combination of metabolomics and transcriptomics. The results showed that both treatments significantly modulated the transcriptome and metabolome of plants under salinity stress, highlighting an induction of the hormonal response. Nevertheless, P and F3 also displayed several peculiarities. F3 specifically modulated the response to ethylene and MAPK signaling pathway, whereas P treatment induced a down-accumulation of secondary metabolites, albeit genes controlling the biosynthesis of osmoprotectants and antioxidants were up-regulated. Moreover, according with the auxin response modulation, P promoted cell wall biogenesis and plasticity in salt-stressed plants. Notably, our data also outlined an epigenetic control of gene expression induced by P treatment. Contrarily, experimental data are just partially in agreement when not stressed plants, treated with P or F3, were considered. Indeed, the reduced accumulation of secondary metabolites and the analyses of hormone pathways modulation would suggest a preferential allocation of resources towards growth, that is not coherent with the down-regulation of the photosynthetic machinery, the CO2 assimilation rate and leaves biomass. In conclusion, our data demonstrate that, although they might activate different mechanisms, both the P and F3 can result in similar benefits, as far as the accumulation of protective osmolytes and the enhanced tolerance to oxidative stress are concerned. Notably, the F3 fraction exhibits slightly greater growth promotion effects under high salt conditions. Most importantly, this research further corroborates that biostimulants' mode of action is dependent on plants' physiological status and their composition, underscoring the importance of investigating the bioactivity of the different molecular components to design tailored applications for the agricultural practice.

The role of Rab GTPase in Plant development and stress

Small GTPase is a type of crucial regulator in eukaryotes. It acts as a molecular switch by binding with GTP and GDP in cytoplasm, affecting various cellular processes. Small GTPase were divided into five subfamilies based on sequence, structure and function: Ras, Rho, Rab, Arf/Sar and Ran, with Rab being the largest subfamily. Members of the Rab subfamily play an important role in regulating complex vesicle transport and microtubule system activity. Plant cells are composed of various membrane-bound organelles, and vesicle trafficking is fundamental to the existence of plants. At present, the function of some Rab members, such as RabA1a, RabD2b/c and RabF2, has been well characterized in plants. This review summarizes the role of Rab GTPase in regulating plant tip growth, morphogenesis, fruit ripening and stress response, and briefly describes the regulatory mechanisms involved. It provides a reference for further alleviating environmental stress, improving plant resistance and even improving fruit quality.

Salinity causes differences in stratigraphic methane sources and sinks

Methane metabolism, driven by methanogenic and methanotrophic microorganisms, plays a pivotal role in the carbon cycle. As seawater intrusion and soil salinization rise due to global environmental shifts, understanding how salinity affects methane emissions, especially in deep strata, becomes imperative. Yet, insights into stratigraphic methane release under varying salinity conditions remain sparse. Here we investigate the effects of salinity on methane metabolism across terrestrial and coastal strata (15-40 m depth) through in situ and microcosm simulation studies. Coastal strata, exhibiting a salinity level five times greater than terrestrial strata, manifested a 12.05% decrease in total methane production, but a staggering 687.34% surge in methane oxidation, culminating in 146.31% diminished methane emissions. Salinity emerged as a significant factor shaping the methane-metabolizing microbial community's dynamics, impacting the methanogenic archaeal, methanotrophic archaeal, and methanotrophic bacterial communities by 16.53%, 27.25%, and 22.94%, respectively. Furthermore, microbial interactions influenced strata system methane metabolism. Metabolic pathway analyses suggested Atribacteria JS1's potential role in organic matter decomposition, facilitating methane production via Methanofastidiosales. This study thus offers a comprehensive lens to comprehend stratigraphic methane emission dynamics and the overarching factors modulating them.

Microbial diversity and functions in saline soils: A review from a biogeochemical perspective

BACKGROUND

Soil salinization threatens food security and ecosystem health, and is one of the important drivers to the degradation of many ecosystems around the world. Soil microorganisms have extremely high diversity and participate in a variety of key ecological processes. They are important guarantees for soil health and sustainable ecosystem development. However, our understanding of the diversity and function of soil microorganisms under the change of increased soil salinization is fragmented.

AIM OF REVIEW

Here, we summarize the changes in soil microbial diversity and function under the influence of soil salinization in diverse natural ecosystems. We particularly focus on the diversity of soil bacteria and fungi under salt stress and the changes in their emerging functions (such as their mediated biogeochemical processes). This study also discusses how to use the soil microbiome in saline soils to deal with soil salinization for supporting sustainable ecosystems, and puts forward the knowledge gaps and the research directions that need to be strengthened in the future.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Due to the rapid development of molecular-based biotechnology (especially high-throughput sequencing technology), the diversity and community composition and functional genes of soil microorganisms have been extensively characterized in different habitats. Clarifying the responding pattern of microbial-mediated nutrient cycling under salt stress and developing and utilizing microorganisms to weaken the adverse effects of salt stress on plants and soil, which are of guiding significance for agricultural production and ecosystem management in saline lands.

Ecophysiological responses of Phragmites australis populations to a tidal flat gradient in the Yangtze River Estuary, China

Phragmites australis is a prevalent species in the Chongming Dongtan wetland and is capable of thriving in various tidal flat environments, including high salinity habitats. P. australis population displays inconsistent ecological performances, highlighting the need to uncover their survival strategies and mechanisms in tidal flats with diverse soil salinities. Upon comparing functional traits of P. australis at multiple tidal flats (low, middle, and high) and their responses to soil physicochemical properties, this study aimed to clarify the salt-tolerant strategy of P. australis and the corresponding mechanisms. These results showed that leaf characteristics, such as specific leaf area and leaf dry matter content, demonstrated more robust stability to soil salinity than shoot height and dry weight. Furthermore, as salt stress intensified, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxisome (POD) in P. australis leaves at low tidal flat exhibited an increased upward trend compared to those at other tidal flats. The molecular mechanism of salt tolerance in Phragmites australis across various habitats was investigated using transcriptome sequencing. Weighted correlation network analysis (WGCNA) combined with differentially expressed genes (DEGs) screened out 3 modules closely related to high salt tolerance and identified 105 core genes crucial for high salt tolerance. Further research was carried out on the few degraded populations at low tidal flat, and 25 core genes were identified by combining WGCNA and DEGs. A decrease in the activity of ferroptosis marker gonyautoxin-4 and an increase in the content of Fe3+ in the degenerated group were observed, indicating that ferroptosis might participate in degradation. Furthermore, correlation analysis indicated a possible regulatory network between salt tolerance and ferroptosis. In short, this study provided new insights into the salt tolerance mechanism of P. australis population along tidal flats.

Effects of Fishery Utilization on the Physicochemical Index and Microbial Community Composition in Saline-Alkaline Water

Fishery utilization of idle saline-alkaline water resources offers various benefits including reducing surrounding soil salinity, improving the ecological environment, increasing arable land area, and providing economic advantages to the fishery industry. However, for decades, the characteristics and regulatory mechanisms of microbial communities that affect fishery utilization have not been clear, which restricts their application. In this study, high-throughput 16S rRNA amplicon sequencing was employed to analyze the bacterial community in these water resources. The sequencing yielded high-quality sequences (2,765,063), resulting in the identification of 18,761 bacterial operational taxonomic units (OTUs). Analysis revealed that the type of saline-alkaline water had a more significant influence on the bacterial community compared to seasonal variations within the aquaculture period. The Chao index for saline-alkaline ponds (ASW) was significantly lower (P < 0.05) than for still saline-alkaline water (SSW) and flowing saline-alkaline water (FSW), while the Shannon index for ASW was also significantly lower (P < 0.05) compared to FSW. When comparing ASW to nonaquaculture saline-alkaline water, a decrease in Proteobacteria to 26.87% was noted, particularly α-proteobacteria and γ-proteobacteria, accompanied by a rapid increase in Actinobacteria and Cyanobacteria to 28.60%. Networkx analysis further revealed that ASW significantly increased competition and amensalism from secondary saline-alkaline water microorganisms, resulting in a more solitary bacterial community composition as an adaptive strategy to cope with intense environmental pressures. Key bacterial species such as Pseudomonas, Hydrogenophaga, and Flavobacterium were found to be involved in hydrogen-cycling, nitrogen-cycling, and carbon-cycling, respectively, with all three exhibiting high abundance in FSW. Consequently, FSW demonstrates significant advantages in biogeochemical cycling, pollutant degradation, and the utilization of indigenous probiotic bacteria. Although the surface of abandoned secondary saline-alkaline land was covered with white salt particles, the fishery utilization of saline-alkaline water with low salinity levels (4.0-5.5), and the presence of nitrate and phosphate were identified as primary determinants of bacterial community composition. Nevertheless, a comparison of coastal high-salinity ponds indicated that salinity still selectively affects bacterial communities to some extent. Overall, our study provides valuable insights into the microbial regulation of nitrite during saline-alkaline water aquaculture, thereby aiding in the efficient utilization of secondary saline-alkaline water resources for fisheries.

Negative correlation between soil salinity and soil organic carbon variability

Soil organic carbon (SOC) is vital for terrestrial ecosystems, affecting biogeochemical processes, and soil health. It is known that soil salinity impacts SOC content, yet the specific direction and magnitude of SOC variability in relation to soil salinity remain poorly understood. Analyzing 43,459 mineral soil samples (SOC < 150 g kg-1) collected across different land covers since 1992, we approximate a soil salinity increase from 1 to 5 dS m-1 in croplands would be associated with a decline in mineral soils SOC from 0.14 g kg-1 above the mean predicted SOC ([Formula: see text] = 18.47 g kg-1) to 0.46 g kg-1 below [Formula: see text] (~-430%), while for noncroplands, such decline is sharper, from 0.96 above [Formula: see text] = 35.96 g kg-1 to 4.99 below [Formula: see text] (~-620%). Although salinity's significance in explaining SOC variability is minor (<6%), we estimate a one SD increase in salinity of topsoil samples (0 to 7 cm) correlates with respective [Formula: see text] declines of ~4.4% and ~9.26%, relative to [Formula: see text] and [Formula: see text]. The [Formula: see text] decline in croplands is greatest in vegetation/cropland mosaics while lands covered with evergreen needle-leaved trees are estimated with the highest [Formula: see text] decline in noncroplands. We identify soil nitrogen, land cover, and precipitation Seasonality Index as the most significant parameters in explaining the SOC's variability. The findings provide insights into SOC dynamics under increased soil salinity, improving understanding of SOC stock responses to land degradation and climate warming.

Creating Climate-Resilient Crops by Increasing Drought, Heat, and Salt Tolerance

Over the years, the changes in the agriculture industry have been inevitable, considering the need to feed the growing population. As the world population continues to grow, food security has become challenged. Resources such as arable land and freshwater have become scarce due to quick urbanization in developing countries and anthropologic activities; expanding agricultural production areas is not an option. Environmental and climatic factors such as drought, heat, and salt stresses pose serious threats to food production worldwide. Therefore, the need to utilize the remaining arable land and water effectively and efficiently and to maximize the yield to support the increasing food demand has become crucial. It is essential to develop climate-resilient crops that will outperform traditional crops under any abiotic stress conditions such as heat, drought, and salt, as well as these stresses in any combinations. This review provides a glimpse of how plant breeding in agriculture has evolved to overcome the harsh environmental conditions and what the future would be like.

Inroads into saline-alkaline stress response in plants: unravelling morphological, physiological, biochemical, and molecular mechanisms

MAIN CONCLUSION

This article discusses the complex network of ion transporters, genes, microRNAs, and transcription factors that regulate crop tolerance to saline-alkaline stress. The framework aids scientists produce stress-tolerant crops for smart agriculture. Salinity and alkalinity are frequently coexisting abiotic limitations that have emerged as archetypal mediators of low yield in many semi-arid and arid regions throughout the world. Saline-alkaline stress, which occurs in an environment with high concentrations of salts and a high pH, negatively impacts plant metabolism to a greater extent than either stress alone. Of late, saline stress has been the focus of the majority of investigations, and saline-alkaline mixed studies are largely lacking. Therefore, a thorough understanding and integration of how plants and crops rewire metabolic pathways to repair damage caused by saline-alkaline stress is of particular interest. This review discusses the multitude of resistance mechanisms that plants develop to cope with saline-alkaline stress, including morphological and physiological adaptations as well as molecular regulation. We examine the role of various ion transporters, transcription factors (TFs), differentially expressed genes (DEGs), microRNAs (miRNAs), or quantitative trait loci (QTLs) activated under saline-alkaline stress in achieving opportunistic modes of growth, development, and survival. The review provides a background for understanding the transport of micronutrients, specifically iron (Fe), in conditions of iron deficiency produced by high pH. Additionally, it discusses the role of calcium in enhancing stress tolerance. The review highlights that to encourage biomolecular architects to reconsider molecular responses as auxiliary for developing tolerant crops and raising crop production, it is essential to (a) close the major gaps in our understanding of saline-alkaline resistance genes, (b) identify and take into account crop-specific responses, and (c) target stress-tolerant genes to specific crops.

Bowl effect of irreversible primary salinization driven by geology in Hetao irrigation area, China

Agricultural irrigation areas around the world employ similar planting methods, but there are notable disparities in salinization mechanism and management strategies. Many scholars have focused on human activities as the main cause of secondary soil salinization, while neglecting the underlying issue of primary soil salinization caused by geological factors. This study takes the Hetao irrigation area in China as a case study, delving into the geological forces responsible for primary salinization. Using historical survey data on geological structure, lake evolution, and sedimentation to analyze the stratigraphic distribution and groundwater storage characteristic. Additionally, using groundwater hydrochemistry data from historical literatures to analyze the concentration, distribution patterns, and source issues of salt ions. The research results show that a novel concept called the "bowl effect" can explain the unique cause of primary salinization in Hetao irrigation area. The bowl effect effectively transforms Hetao irrigation area into an enclosed space, which significantly limits the movement of groundwater and hinders the dilution of highly saline or alkaline water. The bowl effect has broad applicability and can serve as a useful framework for studying primary salinization challenges in agricultural irrigation areas worldwide. This research provides a scientifically reference for selecting salinization control methods, and will benefit local stakeholders, government agencies, and water resource managers.

Microbacterium azadirachtae CNUC13 Enhances Salt Tolerance in Maize by Modulating Osmotic and Oxidative Stress

Soil salinization is one of the leading threats to global ecosystems, food security, and crop production. Plant growth-promoting rhizobacteria (PGPRs) are potential bioinoculants that offer an alternative eco-friendly agricultural approach to enhance crop productivity from salt-deteriorating lands. The current work presents bacterial strain CNUC13 from maize rhizosphere soil that exerted several PGPR traits and abiotic stress tolerance. The strain tolerated up to 1000 mM NaCl and 30% polyethylene glycol (PEG) 6000 and showed plant growth-promoting (PGP) traits, including the production of indole-3-acetic acid (IAA) and siderophore as well as phosphate solubilization. Phylogenetic analysis revealed that strain CNUC13 was Microbacterium azadirachtae. Maize plants exposed to high salinity exhibited osmotic and oxidative stresses, inhibition of seed germination, plant growth, and reduction in photosynthetic pigments. However, maize seedlings inoculated with strain CNUC13 resulted in significantly improved germination rates and seedling growth under the salt-stressed condition. Specifically, compared with the untreated control group, CNUC13-treated seedlings exhibited increased biomass, including fresh weight and root system proliferation. CNUC13 treatment also enhanced photosynthetic pigments (chlorophyll and carotenoids), reduced the accumulation of osmotic (proline) and oxidative (hydrogen peroxide and malondialdehyde) stress indicators, and positively influenced the activities of antioxidant enzymes (catalase, superoxide dismutase, and peroxidase). As a result, CNUC13 treatment alleviated oxidative stress and promoted salt tolerance in maize. Overall, this study demonstrates that M. azadirachtae CNUC13 significantly enhances the growth of salt-stressed maize seedlings by improving photosynthetic efficiency, osmotic regulators, oxidative stress resilience, and antioxidant enzyme activity. These findings emphasize the potential of utilizing M. azadirachtae CNUC13 as a bioinoculant to enhance salt stress tolerance in maize, providing an environmentally friendly approach to mitigate the negative effects of salinity and promote sustainable agriculture.

Enhancement of Nutrient Composition and Non-Volatile Flavor Substances in Muscle Tissue of Red Drum (Sciaenops ocellatus) Through Inland Low Salinity Saline-Alkaline Water Culture

The red drum (Sciaenops ocellatus), a globally significant marine aquaculture species, boasts formidable osmoregulatory capabilities and remarkable adaptability to low salinity, making it an ideal candidate for commercial cultivation in inland low salinity saline-alkaline waters. However, studies on the fundamental nutritional composition and flavor quality of S. ocellatus in these inland low salinity saline-alkaline waters remain unreported. This study delves into the impact of inland low salinity saline-alkaline environments on the basic nutritional components and nonvolatile flavor substances (including free amino acids and free nucleotides) in the muscle tissue of S. ocellatus. The findings reveal that redfish cultivated in these conditions exhibit a significant increase in the crude fat, ash, and protein content in their dorsal muscle tissue, coupled with a decrease in moisture content (p < 0.05), indicating an enhancement in the nutritional value of the dorsal muscle tissue. Furthermore, this cultivation environment significantly elevates the content of free amino acids in the muscle tissue (p < 0.05), particularly those contributing to umami and sweet tastes, while reducing the relative content of bitter amino acids. Although the total content of free nucleotides decreased, the equivalent umami concentration (EUC) in the muscle tissue markedly increased (p < 0.05) due to the synergistic effect of umami amino acids and flavor nucleotides, enhancing the umami taste characteristics. Therefore, inland low salinity saline-alkaline aquaculture not only elevates the nutritional value of S. ocellatus muscle tissue but also improves its umami flavor characteristics. This discovery opens new perspectives for further research into the impact of inland low salinity saline-alkaline environments on the flavor properties of marine animals.

Identification, Classification, and Transcriptional Analysis of Rab GTPase Genes from Tomato (Solanum lycopersicum) Reveals Salt Stress Response Genes

Salinity in plants generates an osmotic and ionic imbalance inside cells that compromises the viability of the plant. Rab GTPases, the largest family within the small GTPase superfamily, play pivotal roles as regulators of vesicular trafficking in plants, including the economically important and globally cultivated tomato (Solanum lycopersicum). Despite their significance, the specific involvement of these small GTPases in tomato vesicular trafficking and their role under saline stress remains poorly understood. In this work, we identified and classified 54 genes encoding Rab GTPases in cultivated tomato, elucidating their genomic distribution and structural characteristics. We conducted an analysis of duplication events within the S. lycopersicum genome, as well as an examination of gene structure and conserved motifs. In addition, we investigated the transcriptional profiles for these Rab GTPases in various tissues of cultivated and wild tomato species using microarray-based analysis. The results showed predominantly low expression in most of the genes in both leaves and vegetative meristem, contrasting with notably high expression levels observed in seedling roots. Also, a greater increase in gene expression in shoots from salt-tolerant wild tomato species was observed under normal conditions when comparing Solanum habrochaites, Solanum pennellii, and Solanum pimpinellifolium with S. lycopersicum. Furthermore, an expression analysis of Rab GTPases from Solanum chilense in leaves and roots under salt stress treatment were also carried out for their characterization. These findings revealed that specific Rab GTPases from the endocytic pathway and the trans-Golgi network (TGN) showed higher induction in plants exposed to saline stress conditions. Likewise, disparities in gene expression were observed both among members of the same Rab GTPase subfamily and between different subfamilies. Overall, this work emphasizes the high degree of conservation of Rab GTPases, their high functional diversification in higher plants, and the essential role in mediating salt stress tolerance and suggests their potential for further exploration of vesicular trafficking mechanisms in response to abiotic stress conditions.

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.

Understanding Salinity-Driven Modulation of Microbial Interactions: Rhizosphere versus Edaphic Microbiome Dynamics

Soil salinization poses a global threat to terrestrial ecosystems. Soil microorganisms, crucial for maintaining ecosystem services, are sensitive to changes in soil structure and properties, particularly salinity. In this study, contrasting dynamics within the rhizosphere and bulk soil were focused on exploring the effects of heightened salinity on soil microbial communities, evaluating the influences shaping their composition in saline environments. This study observed a general decrease in bacterial alpha diversity with increasing salinity, along with shifts in community structure in terms of taxa relative abundance. The size and stability of bacterial co-occurrence networks declined under salt stress, indicating functional and resilience losses. An increased proportion of heterogeneous selection in bacterial community assembly suggested salinity's critical role in shaping bacterial communities. Stochasticity dominated fungal community assembly, suggesting their relatively lower sensitivity to soil salinity. However, bipartite network analysis revealed that fungi played a more significant role than bacteria in intensified microbial interactions in the rhizosphere under salinity stress compared to the bulk soil. Therefore, microbial cross-domain interactions might play a key role in bacterial resilience under salt stress in the rhizosphere.

The urgency of building soils for Middle Eastern and North African countries: Economic, environmental, and health solutions

Soil degradation is a short or long ongoing process that limits ecosystem services. Intensive land use, water scarcity, land disturbance, and global climate change have reduced the quality of soils worldwide. This degradation directly threatens most of the land in the Middle East and North Africa, while the remaining areas are at high risk of further desertification. Rehabilitation and control of these damaged environments are essential to avoid negative effects on human well-being (e.g., poverty, food insecurity, wars, etc.). Here we review constructed soils involving the use of waste materials as a solution to soil degradation and present approaches to address erosion, organic matter oxidation, water scarcity and salinization. Our analysis showed a high potential for using constructed soil as a complimentary reclamation solution in addition to traditional ones. Constructed soils could have the ability to overcome the limitations of existing solutions to tackle land degradation while contributing to the solution of waste management problems. These soils facilitate the provision of multiple ecosystem services and have the potential to address particularly challenging land degradation problems in semi and dry climates.

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.

Stress salinity in plants: New strategies to cope with in the foreseeable scenario

The excess of salts in soils causes stress in most plants, except for some halophytes that can tolerate higher levels of salinity. The excess of Na+ generates an ionic imbalance, reducing the K+ content and altering cellular metabolism, thus impacting in plant growth and development. Additionally, salinity in soil induces water stress due to osmotic effects and increments the production of reactive oxygen species (ROS) that affect the cellular structure, damaging membranes and proteins, and altering the electrochemical potential of H+, which directly affects nutrient absorption by membrane transporters. However, plants possess mechanisms to overcome the toxicity of the sodium ions, such as internalization into the vacuole or exclusion from the cell, synthesis of enzymes or protective compounds against ROS, and the synthesis of metabolites that help to regulate the osmotic potential of plants. Physiologic and molecular mechanisms of salinity tolerance in plants will be addressed in this review. Furthermore, a revision of strategies taken by researchers to confer salt stress tolerance on agriculturally important species are discussed. These strategies include conventional breeding and genetic engineering as transgenesis and genome editing by CRISPR/Cas9.

Calcium regulation of the Arabidopsis Na+/K+ transporter HKT1;1 improves seed germination under salt stress

Calcium is known to improve seed-germination rates under salt stress. We investigated the involvement of calcium ions (Ca2+) in regulating HIGH-AFFINITY K+ TRANSPORTER 1 (HKT1; 1), which encodes a Na+/K+ transporter, and its post-translational regulator TYPE 2C PROTEIN PHOSPHATASE 49 (PP2C49), in germinating Arabidopsis (Arabidopsis thaliana) seedlings. Germination rates of hkt1 mutant seeds under salt stress remained unchanged by CaCl2 treatment in wild-type Arabidopsis, whereas pp2c49 mutant seeds displayed improved salt-stress tolerance in the absence of CaCl2 supplementation. Analysis of HKT1;1 and PP2C49 promoter activity revealed that CaCl2 treatment results in radicle-focused expression of HKT1;1 and reduction of the native radicle-exclusive expression of PP2C49. Ion-content analysis indicated that CaCl2 treatment improves K+ retention in germinating wild-type seedlings under salt stress, but not in hkt1 seedlings. Transgenic seedlings designed to exclusively express HKT1;1 in the radicle during germination displayed higher germination rates under salt stress than the wild type in the absence of CaCl2 treatment. Transcriptome analysis of germinating seedlings treated with CaCl2, NaCl, or both revealed 118 upregulated and 94 downregulated genes as responsive to the combined treatment. Bioinformatics analysis of the upstream sequences of CaCl2-NaCl-treatment-responsive upregulated genes revealed the abscisic acid response element CACGTGTC, a potential CaM-binding transcription activator-binding motif, as most prominent. Our findings suggest a key role for Ca2+ in mediating salt-stress responses during germination by regulating genes that function to maintain Na+ and K+ homeostasis, which is vital for seed germination under salt stress.

Integration of Physiological, Transcriptomic, and Metabolomic Analyses Reveal Molecular Mechanisms of Salt Stress in Maclura tricuspidata

Salt stress is a universal abiotic stress that severely affects plant growth and development. Understanding the mechanisms of Maclura tricuspidate's adaptation to salt stress is crucial for developing salt-tolerant plant varieties. This article discusses the integration of physiology, transcriptome, and metabolome to investigate the mechanism of salt adaptation in M. tricuspidata under salt stress conditions. Overall, the antioxidant enzyme system (SOD and POD) of M. tricuspidata exhibited higher activities compared with the control, while the content of soluble sugar and concentrations of chlorophyll a and b were maintained during salt stress. KEGG analysis revealed that deferentially expressed genes were primarily involved in plant hormone signal transduction, phenylpropanoid and flavonoid biosynthesis, alkaloids, and MAPK signaling pathways. Differential metabolites were enriched in amino acid metabolism, the biosynthesis of plant hormones, butanoate, and 2-oxocarboxylic acid metabolism. Interestingly, glycine, serine, and threonine metabolism were found to be important both in the metabolome and transcriptome-metabolome correlation analyses, suggesting their essential role in enhancing the salt tolerance of M. tricuspidata. Collectively, our study not only revealed the molecular mechanism of salt tolerance in M. tricuspidata, but also provided a new perspective for future salt-tolerant breeding and improvement in salt land for this species.

A new high-resolution global topographic factor dataset calculated based on SRTM

Topography is an important factor affecting soil erosion and is measured as a combination of the slope length and slope steepness (LS-factor) in erosion models, like the Chinese Soil Loss Equation. However, global high-resolution LS-factor datasets have rarely been published. Challenges arise when attempting to extract the LS-factor on a global scale. Furthermore, existing LS-factor estimation methods necessitate projecting data from a spherical trapezoidal grid to a planar rectangle, resulting in grid size errors and high time complexity. Here, we present a global 1-arcsec resolution LS-factor dataset (DS-LS-GS1) with an improved method for estimating the LS-factor without projection conversion (LS-WPC), and we integrate it into a software tool (LS-TOOL). Validation of the Himmelblau-Orlandini mathematical surface shows that errors are less than 1%. We assess the LS-WPC method on 20 regions encompassing 5 landform types, and R2 of LS-factor are 0.82, 0.82, 0.83, 0.83, and 0.84. Moreover, the computational efficiency can be enhanced by up to 25.52%. DS-LS-GS1 can be used as high-quality input data for global soil erosion assessment.

RNA-Seq-Based WGCNA and Association Analysis Reveal the Key Regulatory Module and Genes Responding to Salt Stress in Wheat Roots

Soil salinization is the main abiotic stressor faced by crops. An improved understanding of the transcriptional response to salt stress in roots, the organ directly exposed to a high salinity environment, can inform breeding strategies to enhance tolerance and increase crop yield. Here, RNA-sequencing was performed on the roots of salt-tolerant wheat breeding line CH7034 at 0, 1, 6, 24, and 48 h after NaCl treatment. Based on transcriptome data, a weighted gene co-expression network analysis (WGCNA) was constructed, and five gene co-expression modules were obtained, of which the blue module was correlated with the time course of salt stress at 1 and 48 h. Two GO terms containing 249 differentially expressed genes (DEGs) related to osmotic stress response and salt-stress response were enriched in the blue module. These DEGs were subsequently used for association analysis with a set of wheat germplasm resources, and the results showed that four genes, namely a Walls Are Thin 1-related gene (TaWAT), an aquaporin gene (TaAQP), a glutathione S-transfer gene (TaGST), and a zinc finger gene (TaZFP), were associated with the root salt-tolerance phenotype. Using the four candidate genes as hub genes, a co-expression network was constructed with another 20 DEGs with edge weights greater than 0.6. The network showed that TaWAT and TaAQP were mainly co-expressed with fifteen interacting DEGs 1 h after salt treatment, while TaGST and TaZFP were mainly co-expressed with five interacting DEGs 48 h after salt treatment. This study provides key modules and candidate genes for understanding the salt-stress response mechanism in wheat roots.

Integrated web portal for non-destructive salt sensitivity detection of Camelina sativa seeds using fluorescent and visible light images coupled with machine learning algorithms

Climate change has created unprecedented stresses in the agricultural sector, driving the necessity of adapting agricultural practices and developing novel solutions to the food crisis. Camelina sativa (Camelina) is a recently emerging oilseed crop with high nutrient-density and economic potential. Camelina seeds are rich in essential fatty acids and contain potent antioxidants required to maintain a healthy diet. Camelina seeds are equally amenable to economic applications such as jet fuel, biodiesel and high-value industrial lubricants due to their favorable proportions of unsaturated fatty acids. High soil salinity is one of the major abiotic stresses threatening the yield and usability of such crops. A promising mitigation strategy is automated, non-destructive, image-based phenotyping to assess seed quality in the food manufacturing process. In this study, we evaluate the effectiveness of image-based phenotyping on fluorescent and visible light images to quantify and qualify Camelina seeds. We developed a user-friendly web portal called SeedML that can uncover key morpho-colorimetric features to accurately identify Camelina seeds coming from plants grown in high salt conditions using a phenomics platform equipped with fluorescent and visible light cameras. This portal may be used to enhance quality control, identify stress markers and observe yield trends relevant to the agricultural sector in a high throughput manner. Findings of this work may positively contribute to similar research in the context of the climate crisis, while supporting the implementation of new quality controls tools in the agri-food domain.

Synergistic effect of climate change and water management: Historical and future soil salinity in the Kur-Araz lowland, Azerbaijan

While soil salinization is a major threat to the food security and sustainability of humanity, information on salinization in developing countries is limited. In this study, Landsat data were used to predict the salinization process from 1986 to 2021 in the Kur-Araz lowland of Azerbaijan, and water movement and salinity transport models were developed to calculate the effects of climate change and water management. The model results showed that increases in rainfall and drainage have led to dramatic improvements in soil salinity and agricultural productivity and that these changes were caused by the synergistic effect of climate change and water management. The future predictions indicate that rainfall will decrease due to the decrease in evaporation in the neighboring Caspian Sea, leading to further re-salinization. Soil re-salinization would be a severe threat to the sustainability of the agricultural industry and food security of Azerbaijan and neighboring countries. More scientific attention and efforts should be devoted to developing countries in preparation for the impact of climate change.

Comparative Transcriptome Analysis Provides Insights into the Effect of Epicuticular Wax Accumulation on Salt Stress in Coconuts

The coconut is an important tropical economical crop and exhibits high tolerance to various types of salinity stress. However, little is known about the molecular mechanism underlying its salt tolerance. In this study, RNA-Seq was applied to examine the different genes expressed in four coconut varieties when exposed to a salt environment, resulting in the generation of data for 48 transcriptomes. Comparative transcriptome analysis showed that some genes involved in cutin and wax biosynthesis were significantly upregulated in salt treatment compared to the control, including CYP86A4, HTH, CER1, CER2, CER3, DCR, GPAT4, LTP3, LTP4, and LTP5. In particular, the expression of CER2 was induced more than sixfold, with an RPKM value of up to 205 ten days after salt treatment in Hainan Tall coconut, demonstrating superior capacity in salt tolerance compared to dwarf coconut varieties. However, for yellow dwarf and red dwarf coconut varieties, the expression level of the CER2 gene was low at four different time points after exposure to salt treatment, suggesting that this gene may contribute to the divergence in salt tolerance between tall and dwarf coconut varieties. Cytological evidence showed a higher abundance of cuticle accumulation in tall coconut and severe damage to cuticular wax in dwarf coconut.

Low apoplastic Na+ and intracellular ionic homeostasis confer salinity tolerance upon Ca2SiO4 chemigation in Zea mays L. under salt stress

Salinity is known to have a greater impact on shoot growth than root growth. Na+ buildup in plant tissue under salt stress has been proposed as one of the main issues that causes growth inhibition in crops via ionic imbalances, osmotic stress and pH disturbances. However, the evidence for apoplastic Na+ buildup and the role of silicon in Na+ accumulation at the subcellular level is still enigmatic. The current study focuses on the accumulation of Na+ in the apoplast and symplast of younger and older leaves of two maize varieties (Iqbal as salt-tolerant and Jalal as salt-sensitive) using hydroponic culture along with silicon supplementation under short-term salinity stress. Subcellular ion analysis indicated that silicon nutrition decreased Na+ concentration in both apoplastic washing fluid and symplastic fluid of maize under salt stress. The addition of silicon under NaCl treatment resulted in considerable improvement in fresh biomass, relative water content, chlorophyll content, and concentration of important subcellular ions (i.e., Ca2+, Mg2+, and K+). Knowledge of subcellular ion analysis is essential for solving the mechanisms underlying vital cellular functions e.g. in the current study, the soluble Na+ concentration in the apoplast of older leaves was found to be significantly greater (36.1 mM) in the salt-sensitive variety under NaCl treatment, which was 42.4% higher when compared to the Na+ concentration in the salt-tolerant variety under the same treatment which can influence permeability of cell membrane, signal transduction pathways and provides insights into how ion compartmentalization can contributes to salt tolerance. Calcium silicate enrichment can contribute to increased growth and improved ionic homeostasis by minimizing leaf electrolyte leakage, improving mechanical functions of cell wall and reducing water loss, and improved photosynthetic function. In current investigation, increased water content and intracellular ionic homeostasis along with reduced concentration of Na+ in the maize leaf apoplast suggest that calcium silicate can be used to ameliorate the adverse effects of salt stress and obtain yield using marginal saline lands.

Enhancing salinity tolerance in cucumber through Selenium biofortification and grafting

BACKGROUND

Salinity stress is a major limiting factor for plant growth, particularly in arid and semi-arid environments. To mitigate the detrimental effects of salinity stress on vegetable production, selenium (Se) biofortification and grafting onto tolerant rootstocks have emerged as effective and sustainable cultivation practices. This study aimed to investigate the combined effects of Se biofortification and grafting onto tolerant rootstock on the yield of cucumber grown under salinity stress greenhouse conditions. The experiment followed a completely randomized factorial design with three factors: salinity level (0, 50, and 100 mM of NaCl), foliar Se application (0, 5, and 10 mg L-1 of sodium selenate) and grafting (grafted and non-grafted plants) using pumpkin (Cucurbita maxima) as the rootstock. Each treatment was triplicated.

RESULTS

The results of this study showed that Se biofortification and grafting significantly enhanced salinity tolerance in grafted cucumbers, leading to increased yield and growth. Moreover, under salinity stress conditions, Se-Biofortified plants exhibited increased leaf relative water content (RWC), proline, total soluble sugars, protein, phenol, flavonoids, and antioxidant enzymes. These findings indicate that Se contributes to the stabilization of cucumber cell membrane and the reduction of ion leakage by promoting the synthesis of protective compounds and enhancing antioxidant enzyme activity. Moreover, grafting onto pumpkin resulted in increased salinity tolerance of cucumber through reduced Na uptake and translocation to the scion.

CONCLUSION

In conclusion, the results highlight the effectiveness of Se biofortification and grafting onto pumpkin in improving cucumber salinity tolerance. A sodium selenate concentration of 10 mg L-1 is suggested to enhance the salinity tolerance of grafted cucumbers. These findings provide valuable insights for the development of sustainable cultivation practices to mitigate the adverse impact of salinity stress on cucumber production in challenging environments.

Survival strategies of Bacillus spp. in saline soils: Key factors to promote plant growth and health

Soil salinity is one of the most important abiotic factors that affects agricultural production worldwide. Because of saline stress, plants face physiological changes that have negative impacts on the various stages of their development, so the employment of plant growth-promoting bacteria (PGPB) is one effective means to reduce such toxic effects. Bacteria of the Bacillus genus are excellent PGPB and have been extensively studied, but what traits makes them so extraordinary to adapt and survive under harsh situations? In this work we review the Bacillus' innate abilities to survive in saline stressful soils, such as the production osmoprotectant compounds, antioxidant enzymes, exopolysaccharides, and the modification of their membrane lipids. Other survival abilities are also discussed, such as sporulation or a reduced growth state under the scope of a functional interaction in the rhizosphere. Thus, the most recent evidence shows that these saline adaptive activities are important in plant-associated bacteria to potentially protect, direct and indirect plant growth-stimulating activities. Additionally, recent advances on the mechanisms used by Bacillus spp. to improve the growth of plants under saline stress are addressed, including genomic and transcriptomic explorations. Finally, characterization and selection of Bacillus strains with efficient survival strategies are key factors in ameliorating saline problems in agricultural production.

Salt Tolerance in Soybeans: Focus on Screening Methods and Genetics

Salinity greatly affects the production of soybeans in arid and semi-arid lands around the world. The responses of soybeans to salt stress at germination, emergence, and other seedling stages have been evaluated in multitudes of studies over the past decades. Considerable salt-tolerant accessions have been identified. The association between salt tolerance responses during early and later growth stages may not be as significant as expected. Genetic analysis has confirmed that salt tolerance is distinctly tied to specific soybean developmental stages. Our understanding of salt tolerance mechanisms in soybeans is increasing due to the identification of key salt tolerance genes. In this review, we focus on the methods of soybean salt tolerance screening, progress in forward genetics, potential mechanisms involved in salt tolerance, and the importance of translating laboratory findings into field experiments via marker-assisted pyramiding or genetic engineering approaches, and ultimately developing salt-tolerant soybean varieties that produce high and stable yields. Progress has been made in the past decades, and new technologies will help mine novel salt tolerance genes and translate the mechanism of salt tolerance into new varieties via effective routes.