Annual Halophyte Research Articles

Cakile maritima: A Halophyte Model to Study Salt Tolerance Mechanisms and Potential Useful Crop for Sustainable Saline Agriculture in the Context of Climate Change.

Salinity is an increasing problem for agriculture. Most plant species tolerate low or, at best, moderate soil salinities. However, a small (<1%) proportion of species, termed halophytes, can survive and complete their life cycle in natural habitats with salinities equivalent to 200 mM NaCl or more. Cakile maritima is a succulent annual halophyte belonging to the Brassicaceae family; it is dispersed worldwide and mainly grows in foreshores. Cakile maritima growth is optimal under slight (i.e., 100 mM NaCl) saline conditions, measured by biomass and seed production. Higher salt concentrations, up to 500 mM NaCl, significantly impact its growth but do not compromise its survival. Cakile maritima alleviates sodium toxicity through different strategies, including anatomical and morphological adaptations, ion transport regulation, biosynthesis of osmolytes, and activation of antioxidative mechanisms. The species is potentially useful as a cash crop for the so-called biosaline agriculture due to its production of secondary metabolites of medical and nutritional interest and the high oil accumulation in its seeds. In this review, we highlight the relevance of this species as a model for studying the basic mechanisms of salt tolerance and for sustainable biosaline agriculture in the context of soil salination and climate change.

Specificity of Heavy Metal Accumulation in Two Annual Halophytes (Amaranthaceae) with Different Mechanisms of Salt Accumulation under Natural Conditions

Specificity of Heavy Metal Accumulation in Two Annual Halophytes (Amaranthaceae) with Different Mechanisms of Salt Accumulation under Natural Conditions

Soil salinity regulates spatial-temporal heterogeneity of seed germination and seedbank persistence of an annual diaspore-trimorphic halophyte in northern China

Background and aimsSeed heteromorphism is a plant strategy that an individual plant produces two or more distinct types of diaspores, which have diverse morphology, dispersal ability, ecological functions and different effects on plant life history traits. The aim of this study was to test the effects of seasonal soil salinity and burial depth on the dynamics of dormancy/germination and persistence/depletion of buried trimorphic diaspores of a desert annual halophyte Atriplex centralasiatica.MethodsWe investigated the effects of salinity and seasonal fluctuations of temperature on germination, recovery of germination and mortality of types A, B, C diaspores of A. centralasiatica in the laboratory and buried diaspores in situ at four soil salinities and three depths. Diaspores were collected monthly from the seedbank from December 2016 to November 2018, and the number of viable diaspores remaining (not depleted) and their germinability were determined.ResultsNon-dormant type A diaspores were depleted in the low salinity “window” in the first year. Dormant diaspore types B and C germinated to high percentages at 0.3 and 0.1 mol L-1 soil salinity, respectively. High salinity and shallow burial delayed depletion of diaspore types B and C. High salinity delayed depletion time of the three diaspore types and delayed dormancy release of types B and C diaspores from autumn to spring. Soil salinity modified the response of diaspores in the seedbank by delaying seed dormancy release in autum and winter and by providing a low-salt concentration window for germination of non-dormant diaspores in spring and early summer.ConclusionsBuried trimorphic diaspores of annual desert halophyte A. centralasiatica exhibited diverse dormancy/germination behavior in respond to seasonal soil salinity fluctuation. Prolonging persistence of the seedbank and delaying depletion of diaspores under salt stress in situ primarily is due to inhibition of dormancy-break. The differences in dormancy/germination and seed persistence in the soil seedbank may be a bet-hadging strategy adapted to stressful temporal and spatial heterogeneity, and allows A. centralasiatica to persist in the unpredictable cold desert enevironment.

Continuous planting of euhalophyte Suaeda salsa enhances microbial diversity and multifunctionality of saline soil.

Halophyte-based remediation emerges as a novel strategy for ameliorating saline soils, offering a sustainable alternative to conventional leaching methods. While bioremediation is recognized for its ability to energize soil fertility and structure, the complex interplays among plant traits, soil functions, and soil microbial diversity remain greatly unknown. Here, we conducted a 5-year field experiment involving the continuous cultivation of the annual halophyte Suaeda salsa in saline soils to explore soil microbial diversity and their relationships with plant traits and soil functions. Our findings demonstrate that a decline in soil salinity corresponded with increases in the biomass and seed yield of S. salsa, which sustained a consistent seed oil content of approximately 22% across various salinity levels. Significantly, prolonged cultivation of halophytes substantially augmented soil microbial diversity, particularly from the third year of cultivation. Moreover, we identified positive associations between soil multifunctionality, seed yield, and taxonomic richness within a pivotal microbial network module. Soils enriched with taxa from this module showed enhanced multifunctionality and greater seed yields, correlating with the presence of functional genes implicated in nitrogen fixation and nitrification. Genomic analysis suggests that these taxa have elevated gene copy numbers of crucial functional genes related to nutrient cycling. Overall, our study emphasizes that the continuous cultivation of S. salsa enhances soil microbial diversity and recovers soil multifunctionality, expanding the understanding of plant-soil-microbe feedback in bioremediation.IMPORTANCEThe restoration of saline soils utilizing euhalophytes offers a viable alternative to conventional irrigation techniques for salt abatement and soil quality enhancement. The ongoing cultivation of the annual Suaeda salsa and its associated plant traits, soil microbial diversity, and functionalities are, however, largely underexplored. Our investigation sheds light on these dynamics, revealing that cultivation of S. salsa sustains robust plant productivity while fostering soil microbial diversity and multifunctionality. Notably, the links between enhanced soil multifunctionality, increased seed yield, and network-dependent taxa were found, emphasizing the importance of key microbial taxa linked with functional genes vital to nitrogen fixation and nitrification. These findings introduce a novel understanding of the role of soil microbes in bioremediation and advance our knowledge of the ecological processes that are vital for the rehabilitation of saline environments.

Macronutrients and their ratios in different plant species growing in solonchaks of Western Transbaikalia

The macroelement composition and ratios of macroelements in dominant and co-dominant plants growing on lakeside solonchaks of Western Transbaikalia: from salt-sandy strips on dried shoals with pioneer groupings, side slopes to plains with cheieves, irises and leymus communities were studied for the first time. General regularities characterizing their macroelement composition were established for annual halophytes of salt-sand strips of the Beloe Lake shoreline. It has been revealed that pioneer perennials are formed on the mortmass of annuals. Mortmass of different duration of formation was characterized by high silicic content and concentrations of S, Fe, and Mg with a minimal amount of K, and the K : Na ratio was 0.03–0.04. Biological productivity of lakeside saltmarsh communities was determined to be normal and elevated, 1490–3080 g dry mass/m2/year. Species differed significantly in the macroelement composition depending on the conditions of growing in the coastal zone of brackish lakes. Common for the chemical composition of plants was a relatively high content of nitrogen and ash. It was found that by the total concentration of K, Ca, Mg, Na, Si in the dry matter, annuals of the Chenopodiaceae family dominated due to the high amount of sodium. In spite of non-compliance with the norms of the ratios of most macronutrients in the dry matter of plants, especially by K : (Ca + Mg) and K : Na, all species are used as fodder in different periods of the year.

Nutrients and phytochemical density in Mesembryanthemum crystallinum L. cultivated in growing media supplemented with dosages of nitrogen fertilizer

Mesembryanthemum crystallinum L. is an annual halophyte that originated from southern Africa. However, little has been reported about factors that modulate the quantity of secondary metabolites in the plant. In this study, the twin effect of different nitrogen concentrations (0.36, 0.6, 0.8 g/L) and growing media (LECA clay, peat, vermiculite and silica sand) on plant growth, chlorophyll contents, minerals, proximate and antioxidant metabolites in hydroponically cultivated M. crystallinum was investigated. This is important to determine the dosage of N fertilizer that will optimize the bio-productivity and biosynthesis of secondary metabolites and antioxidants in M. crystallinum grown in a hydroponic system. The untreated plant (0 g/L N) was taken as the control. At the end of the experiment, optimum yields in leaf number (9.2), fresh weight (50.40 g), Ca, N, and Protein (34.04 %) were recorded in M. crystallinum grown with peat enhanced with different dosages of N-fertilizer. Likewise, chlorophyll level, dry weight, ABTS/TEAC, FRAP, ADF and NDF contents were optimized in LECA clay treated with N-fertilizer. Silica sand with 0.36 g/L dosage of nitrogen fertilizer optimized P, Mn and Zn levels, so also the moisture (9.83 % at 0.8 g/L N), fat (2.38 %, 0 g/L N) and carbohydrates (44.98 and 44.95 %). The highest ash content, Mg and Fe were recorded in the untreated vermiculite as well as polyphenols and K, at 0.6 g/L; Cu and root length (14.60 cm), at 0.8 g/L. In conclusion, different dosages of nitrogen fertilizer and growing media could enhance the growth potential, chlorophyll, phytochemicals, and nutritional properties of M. crystallinum.

Genome-Wide Development of Polymorphic Microsatellite Markers and Genetic Diversity Analysis for the Halophyte Suaeda aralocaspica (Amaranthaceae).

Suaeda aralocaspica, which is an annual halophyte, grows in saline deserts in Central Asia with potential use in saline soil reclamation and salt tolerance breeding. Studying its genetic diversity is critical for effective conservation and breeding programs. In this study, we aimed to develop a set of polymorphic microsatellite markers to analyze the genetic diversity of S. aralocaspica. We identified 177,805 SSRs from the S. aralocaspica genome, with an average length of 19.49 bp, which were present at a density of 393.37 SSR/Mb. Trinucleotide repeats dominated (75.74%) different types of motifs, and the main motif was CAA/TTG (44.25%). We successfully developed 38 SSR markers that exhibited substantial polymorphism, displaying an average of 6.18 alleles with accompanying average polymorphism information content (PIC) value of 0.516. The markers were used to evaluate the genetic diversity of 52 individuals collected from three populations of S. aralocaspica in Xinjiang, China. The results showed that the genetic diversity was moderate to high, with a mean expected heterozygosity (He) of 0.614, a mean Shannon's information index (I) of 1.23, and a mean genetic differentiation index (Fst) of 0.263. The SSR markers developed in this study provide a valuable resource for future genetic studies and breeding programs of S. aralocaspica, and even other species in Suaeda.

Characterization of leaf trichomes and their influence on surface wettability of Salsola ferganica, an annual halophyte in the desert.

Many organisms use functional surfaces to collect water from the atmosphere. Salsola ferganica Drob. is one of the most abundant plants in desert regions and thrives in extreme environments with multiple but limited water resources, including dew and fog; however, its mechanisms of water harvesting remain unclear. We investigated trichome structural characteristics and their influence on the surface wettability of S. ferganica leaves using a variety of approaches (scanning electron microscopy, optical microscopy, immunolabelling staining, x-ray diffractometry, and infrared spectroscopy). Microstructural observations revealed that the trichomes of S. ferganica presented a curved upper part, the 'spindle node'-like structure in the middle, and the micro-grooves structure in between; such unique structures may aid in capturing moisture from the air. The physicochemical characteristics of the trichome surface, including hydrophobic functional groups, hydrophilic pectins, and low crystallinity, may enhance the adhesion of water drops to trichomes. Furthermore, we discovered that the piliferous S. ferganica leaves were more effective in retaining water than the glabrous S. aralocaspica leaves, and the dense trichome layer exhibited a significantly unwettable surface (high contact angle with droplets), whereas the individual trichomes retained water effectively (more so under drought conditions). The combination of these two properties is consistent with the 'rose petal effect', which describes rough surfaces that are hydrophobic but exhibit high adhesion with water. These factors suggest that the evolutionary optimisation of water acquisition by coupling relevant microstructures with the physicochemical properties of trichomes enables S. ferganica to survive harsh conditions in the seedling stage.

CgMYB1, an R2R3-MYB transcription factor, can alleviate abiotic stress in an annual halophyte Chenopodium glaucum

MYB transcription factors (TFs) are important regulators of the stress response in plants. In the present study, we characterized the CgMYB1 gene in Chenopodium glaucum, a member of the R2R3-MYB TF family. CgMYB1 was located in the nucleus with an activating domain at the C terminus. The CgMYB1 gene could be induced by salt and cold stress in C. glaucum. Overexpressing CgMYB1 in Arabidopsis significantly enhanced salt and cold tolerance, probably by improving physiological performance and stress-related gene expression. Further analysis suggests that the positive response of CgMYB1 to abiotic stress may partially be attributed to the interaction between CgMYB1 and the CgbHLH001 promoter followed by activation of downstream stress-responsive genes, which mediates stress tolerance. Our findings should contribute to further understanding of the function of R2R3 MYB TF in response to abiotic stress.

Morphogenesis and cell wall composition of trichomes and their function in response to salt in halophyte Salsola ferganica

BackgroundTo survive harsh environmental conditions, desert plants show various adaptions, such as the evolution of trichomes, which are protective epidermal protrusions. Currently, the morphogenesis and function of trichomes in desert plants are not well understood. Salsola ferganica is an annual halophyte distributed in cold deserts; at the seedling stage, its rod-shaped true leaves are covered with long and thick trichomes and are affected by habitat conditions. Therefore, we evaluated the trichomes on morphogenesis and cell wall composition of S. ferganica compared to Arabidopsis thaliana and cotton, related gene expression, and preliminary function in salt accumulation of the leaves.ResultsThe trichomes of S. ferganica were initiated from the epidermal primordium, followed by two to three rounds of cell division to form a multicellular trichome, while some genes associated with them were positively involved. Cell wall composition analysis showed that different polysaccharides including heavily methyl-esterified and fully de-esterified pectins (before maturation, probably in the primary wall), xyloglucans (in the mid-early and middle stages, probably in the secondary wall), and extensin (during the whole developmental period) were detected, which were different from those found in trichomes of Arabidopsis and cotton. Moreover, trichome development was affected by abiotic stress, and might accumulate salt from the mesophyll cells and secrete outside.ConclusionsS. ferganica has multicellular, non-branched trichomes that undergo two to three rounds of cell division and are affected by abiotic stress. They have a unique cell wall composition which is different from that of Arabidopsis and cotton. Furthermore, several genes positively or negatively regulate trichome development. Our findings should contribute to our further understanding of the biogenesis and adaptation of plant accessory structures in desert plant species.

Population Dynamic of the Annual Halophyte Salicornia ramosissima in Salt Pans: Towards a Sustainable Exploitation of Its Wild Populations.

Halophyte species growing under stressful conditions, such as the annual species of the Salicornia genus, have been recognized as a source of metabolites of pharmacological and nutraceutical interest. Therefore, planning the extraction of individual plants from wild populations in a sustainable way is especially important in the case of annual species. We studied the environmental matrix and population dynamic of four Salicornia ramosissima populations growing at two elevations in salt pans under a Mediterranean climate. In elevated areas, S. ramosissima populations presented maximum plant densities of between 628–6288 plants m−2 that remained almost constant until fruiting. In contrast, populations in depressed zones presented five-times greater soil-seed-bank densities and maximum plant densities than populations in elevated zones. In this context, populations in depressed zones lost c. 60% of their maximum plant densities from the end of spring and through summer. In whatever way the environmental matrix seemed to control the population dynamic of S. ramosissima in depressed zones, the effects of a stressful environment would interact with plant densities. In this sense, we recorded the density-dependent mortality for the densest population (max. 51,558 plants m−2). Our results are useful for planning a sustainable harvesting of natural populations of S. ramosissima.

Growth and salt accumulation capacity of the common ice plant in the tsunami-affected soil

ABSTRACT Halophytes are salt-tolerant plant that grows naturally in saline areas where almost all conventional crops die due to NaCl toxicity. The common ice plant, Mesembryanthemum crystallinum L., an annual halophyte native to South Africa, tolerates high salinity levels and accumulates NaCl in a shoot at a high level. To check the availability of the ice plant for desalinization of soils, we cultured the ice plant in soils collected from 16 sites located along coastal regions in the prefectures of Miyagi and Iwate, where were attacked by the tsunami disaster in the wake of the 2011 earthquake off the Pacific coast of Tohoku on 11 March 2011. In the soils obtained from some tsunami affected areas, the growth was better than that in the non-contaminated soil. The factors associated with growth inhibition were suggested to be water ratio (an index of water content) and soil water permeability. The ice plant’s estimated biological yield ranged from 0.33 to 14.6 kg m−2, equivalent to 2.3 to 101.7 t ha−1. The sum of Na+ and Cl− was about 9.5 g in the shoot (31.8% on a dry weight basis), and the estimated total amount of these ions removed from salinized soil was 2.38 t ha−1. These results indicated that the common ice plant could be used as a crop under salinity and a tool for ameliorating NaCl from salinized soils.

The Developmental Delay of Seedlings With Cotyledons Only Confers Stress Tolerance to Suaeda aralocaspica (Chenopodiaceae) by Unique Performance on Morphology, Physiology, and Gene Expression.

Cotyledons play an important role in seedling establishment, although they may just exist for a short time and become senescent upon the emergence of euphylla. So far, the detailed function of cotyledons has not been well understood. Suaeda aralocaspica is an annual halophyte distributed in cold deserts; its cotyledons could exist for a longer time, even last until maturity, and they must exert a unique function in seedling development. Therefore, in this study, we conducted a series of experiments to investigate the morphological and physiological performances of cotyledons under salt stress at different developmental stages. The results showed that the cotyledons kept growing slowly to maintain the normal physiological activities of seedlings by balancing phytohormone levels, accumulating osmoprotectants and antioxidants, and scavenging reactive oxygen species (ROS). Salt stress activated the expression of osmoprotectant-related genes and enhanced the accumulation of related primary metabolites. Furthermore, differentially expressed transcriptional profiles of the cotyledons were also analyzed by cDNA-AFLP to gain an understanding of cotyledons in response to development and salt stress, and the results revealed a progressive increase in the expression level of development-related genes, which accounted for a majority of the total tested TDFs. Meanwhile, key photosynthetic and important salt stress-related genes also actively responded. All these performances suggest that “big cotyledons” are experiencing a delayed but active developmental process, by which S. aralocaspica may survive the harsh condition of the seedling stage.

Optimum Sterilization Method for In Vitro Cultivation of Dimorphic Seeds of the Succulent Halophyte Suaeda aralocaspica

Suaeda aralocaspica is an annual halophyte in the Amaranthaceae in the saline deserts of central Asia. This plant has succulent leaves and grape-like fruits and is a potential horticultural plant. To obtain the efficient sterilization method and optimal culture conditions, two types of seeds produced from a single plant of S. aralocaspica were treated with 75% ethanol for different time durations first, and then sodium hypochlorite (NaClO) or mercury chloride (HgCl2), with five different timing treatments were used for second seed surface sterilization. Sterilized seeds were germinated on a Murashige and Skoog (MS) medium at different potential hydrogenation (pH) levels, to examine germination and seedling performance. The results showed that the highest germination percentage of brown seeds was 100% and that of black seeds was 17%. Thus, brown seeds were more suitable for further culture experiments than black seeds. For brown seeds, the sterilization effect of NaClO was better than that of HgCl2, based on the results of seed germination, contamination, and seedling survival. Rinsing with 75% ethanol for 60 s, sterilizing with NaClO for 8 min, and cultivating at pH 8.0 MS for 7 days was the best of all sterilization procedures and cultivation methods tested, which has been successfully applied to S. aralocaspica in vitro culture. The optimized protocol described here can be used as the reference for the Suaeda genus.

Sanguibacter suaedae sp. nov., isolated from the root of Suaeda aralocaspica in north-west PR China.

A bacterial strain, designated YZGR15T, was isolated from the root of an annual halophyte Suaeda aralocaspica, collected from the southern edge of the Gurbantunggut desert, north-west PR China. Cells of the isolate were Gram-stain-positive, facultatively anaerobic, irregular rods. Growth occurred at 4-42 °C (optimum, 30-37 °C), at pH 6.0-9.0 (optimum, pH 7.0-7.5) and in the presence of 0-9 % (w/v) NaCl (optimum, 2-5 %). Phylogenetic analysis using 16S rRNA gene sequences indicated that strain YZGR15T showed the highest sequence similarity to Sanguibacter keddieii (98.27 %), Sanguibacter antarcticus (98.20 %) and Sanguibacter inulinus (98.06 %). Results of genome analyses of strain YZGR15T indicated that the genome size was 3.16 Mb, with a genomic DNA G+C content of 71.9 mol%. Average nucleotide identity and digital DNA-DNA hybridization values between strain YZGR15Tand three type strains were in the range of 76.5-77.8 % and 20.0-22.2 %, respectively. Analysis of the cellular component of strain YZGR15T revealed that the primary fatty acids were anteiso-C15 : 0, C16 : 0, C14 : 0 and iso-C16 : 0 and the polar lipids included diphosphatidylglycerol, phosphatidylglycerol, three unidentified phospholipids and two unidentified glycolipids. The cell-wall characteristic amino acids were glutamic acid, alanine and an unknown amino acid. The whole-cell sugars for the strain were mannose, ribose, rhamnose, glucose and an unidentified sugar. The predominant respiratory quinone was MK-9(H4). Based on the results of genomic, phylogenetic, phenotypic and chemotaxonomic analyses, strain YZGR15T represents a novel species of the genus Sanguibacter, for which the name Sanguibacter suaedae sp. nov. is proposed. The type strain is YZGR15T (=CGMCC 1.18691T=KCTC 49659T).

Great granny still ruling from the grave: Phenotypical response of plant performance and seed functional traits to salt stress affects multiple generations of a halophyte

Abstract Environmental changes, for example, in rainfall and land use, lead to changes in the environment experienced by subsequent generations of plant species. Environmental conditions of maternal plants can influence the fitness and phenotypes of subsequent generations via non‐genetic mechanisms: transgenerational plasticity (TGP). However, relevant empirical evidence remains scarce and ambiguous. What are the adaptive consequences of TGP for plants in the face of environmental change? For how many generations does the TGP effect remain? We tried to answer these questions by measuring life‐history traits and reproductive characteristics of progeny plants of the diaspore‐heteromorphic annual halophyte Atriplex centralasiatica in a 3‐year TGP experiment covering F0, F1 and F2 and partly F3. Plants from diaspore types A (low dispersal and high germination ability) and C (high dispersal and low germination ability) were grown in favourable versus stressful salinities over three generations in a fully factorial design. Transgenerational plasticity of plants grown in favourable versus stressful salinities decreased from F2 → F1 → F0. Compared to the favourable condition, the stressful condition decreased the length of the vegetative period, increased the length of reproductive time, reproductive allocation and progeny diaspore size. Salinity tolerance and phenotypic plasticity were higher in plants from diaspore A than in those from diaspore C. In the stressful condition, plants produced less plant biomass, larger diaspores, a higher proportion of diaspore C, but lower proportion of diaspore A. Production of the proportion of diaspore C increased with increase in number of previous generations that experienced stress. The stress experience of the great‐great grandmother (F0) continued into the lower A:C ratio of the F3 diaspores. Synthesis. Our findings provide evidence for the ‘escape strategy’ of A. centralasiatica: TGP could spread the risk of environmental adversity by delaying seed germination temporally and broadening seed dispersal spatially, thus allowing plants to cope with environmental heterogeneity. Specifically, the trade‐off in reproductive allocation between diaspores A and C enables plants to develop divergent strategies. New research should reveal the extent to which wide‐ranging taxa can benefit from TGP and whether even (great)‐great grandmother might be the starting point of TGP.

Genome-Wide Identification and Analysis of the Phosphoenolpyruvate Carboxylase Gene Family in Suaeda aralocaspica, an Annual Halophyte With Single-Cellular C4 Anatomy

Phosphoenolpyruvate carboxylase (PEPC) plays pivotal roles in the carbon fixation of photosynthesis and a variety of metabolic and stress pathways. Suaeda aralocaspica belongs to a single-cellular C4 species and carries out a photosynthetic pathway in an unusually elongated chlorenchyma cell, which is expected to have PEPCs with different characteristics. To identify the different isoforms of PEPC genes in S. aralocaspica and comparatively analyze their expression and regulation patterns as well as the biochemical and enzymatic properties in this study, we characterized a bacterial-type PEPC (BTPC; SaPEPC-4) in addition to the two plant-type PEPCs (PTPCs; SaPEPC-1 and SaPEPC-2) using a genome-wide identification. SaPEPC-4 presented a lower expression level in all test combinations with an unknown function; two SaPTPCs showed distinct subcellular localizations and different spatiotemporal expression patterns but positively responded to abiotic stresses. Compared to SaPEPC-2, the expression of SaPEPC-1 specifically in chlorenchyma cell tissues was much more active with the progression of development and under various stresses, particularly sensitive to light, implying the involvement of SaPEPC-1 in a C4 photosynthetic pathway. In contrast, SaPEPC-2 was more like a non-photosynthetic PEPC. The expression trends of two SaPTPCs in response to light, development, and abiotic stresses were also matched with the changes in PEPC activity in vivo (native) or in vitro (recombinant), and the biochemical properties of the two recombinant SaPTPCs were similar in response to various effectors while the catalytic efficiency, substrate affinity, and enzyme activity of SaPEPC-2 were higher than that of SaPEPC-1 in vitro. All the different properties between these two SaPTPCs might be involved in transcriptional (e.g., specific cis-elements), posttranscriptional [e.g., 5′-untranslated region (5′-UTR) secondary structure], or translational (e.g., PEPC phosphorylation/dephosphorylation) regulatory events. The comparative studies on the different isoforms of the PEPC gene family in S. aralocaspica may help to decipher their exact role in C4 photosynthesis, plant growth/development, and stress resistance.

Seed bank dynamics of the annual halophyte Salicornia ramosissima: towards a sustainable exploitation of its wild populations

Halophytes are able to survive in the high salted areas of the world, and have been recognized as sources of bioactive metabolites. There is a need to design sustainable strategies for the use of wild populations of halophytic species in order to avoid irrational gathering. Seed banks are essential for resilience and regeneration in salty ecosystems. We sampled annual seed production, aerial and soil seed banks and seed dynamics for a year in four wild populations of the annual halophyte Salicornia ramosissima growing in saltpans, in order to develop sustainable management practices for the use of its populations. The seed production of S. ramosissima depended mainly on plant density rather than on the number of seeds produced by each individual plant. In three of the four study populations, most of the annual seed production was exported out of the saltpans (> 79%) and only between 14 and 20% was accumulated in the initial aerial and soil seed banks. These initial seed banks were highly depleted during the year until the next fruiting period, when they accumulated less than 1% of the annual seed production (from 19 to 15,302 seed m−2). Salicornia ramosissima established a persistent soil seed bank in two of the four locations. Annual seed production would be key for the preservation of those S. ramosissima populations that do not establish persistent soil seed banks. In view of our results, each population of S. ramosissima should be studied independently to design population-specific management plans.

Differential Accumulation of Metabolites in Suaeda Species Provides New Insights into Abiotic Stress Tolerance in C4-Halophytic Species in Elevated CO2 Conditions

Halophytic plants can adapt to grow and thrive in highly saline conditions. Suaeda species are annual halophytes with high salt tolerance and are most suitable in the restoration of salinized or contaminated saline land and as food, forage, medicine, and bioenergy. In this study, we comprehensively analyzed the different metabolic responses of Suaeda species under salt and drought stress at ambient and elevated CO2 conditions. Seedlings of Suaeda species were treated with 500 mM NaCl and 5% of polyethylene glycol under elevated CO2 stress conditions for 24 h. Then, widely untargeted metabolites were detected by gas chromatography–mass spectrometry. Different metabolites involved in amino acid metabolism, glycolysis, photorespiration, and tricarboxylic acid cycle were quantitatively determined after stress treatments. A total of 61 primary metabolites were annotated. Different treatments increased the contents of certain metabolites, such as amino acids, sugars, and organic acids, as well as some antioxidants, such as quininic acid, kaempferol, and melatonin. These substances may be correlated with osmotic tolerance, increased antioxidant activity, and medical and nutritional value in the species. This study suggests that various metabolites differentially accumulated in C4Suaeda species under varying stress conditions. Furthermore, this work provides new insights into the key secondary metabolite pathway involved in stress tolerance.

Reclamation of saline soil by planting annual euhalophyte Suaeda salsa with drip irrigation: A three-year field experiment in arid northwestern China

Soil salinization threatens agricultural sustainability, especially for arid and semiarid regions. Planting euhalophytes with drip irrigation is proposed to be a feasible solution for the reclamation of saline soils. Thus, by planting an annual halophyte Suaeda salsa with drip irrigation, we assessed the potential of S. salsa to accumulate high amount of salt from soil and change in soil salinity levels in a three-year field study in arid northwestern China. The aboveground parts of S. salsa contained >20% ash salt on a dry weight basis and Na+ and Cl− were the main components. For each year, salt extraction by the aboveground part of S. salsa was ranged from 3749 to 3911 kg ha−1. Soil salinity dramatically decreased year by year by the cultivation of S. salsa, especially in the topsoil layer (0–40 cm). Our study suggested that consecutive cultivation of S. salsa with drip-irrigation is an efficient method to reclaim saline soil in arid and semiarid regions.