Rhizospheric bacteria from the Atacama Desert hyper-arid core: cultured community dynamics and plant growth promotion.

The Atacama Desert is the oldest and driest desert on Earth, encompassing great temperature variations, high ultraviolet radiation, drought, and high salinity, making it ideal for studying the limits of life and resistance strategies. It is also known for harboring a great biodiversity of adapted life forms. While desertification is increasing as a result of climate change and human activities, it is necessary to optimize soil and water usage, where stress-resistant crops are possible solutions. As many studies have revealed the great impact of the rhizobiome on plant growth efficiency and resistance to abiotic stress, we set up to explore the rhizospheric soils of Suaeda foliosa and Distichlis spicata desert plants. By culturing these soils and using 16S rRNA amplicon sequencing, we address community taxonomy composition dynamics, stability through time, and the ability to promote lettuce plant growth. The rhizospheric soil communities were dominated by the families Pseudomonadaceae, Bacillaceae, and Planococcaceae for S. foliosa and Porphyromonadaceae and Haloferacaceae for D. spicata. Nonetheless, the cultures were completely dominated by the Enterobacteriaceae family (up to 98%). Effectively, lettuce plants supplemented with the cultures showed greater size and biomass accumulation. We identified 12 candidates that could be responsible for these outcomes, of which 5 (Enterococcus, Pseudomonas, Klebsiella, Paenisporosarcina, and Ammoniphilus) were part of the built co-occurrence network. We aim to contribute to the efforts to characterize the microbial communities as key for the plant's survival in extreme environments and as a possible source of consortia with plant growth promotion traits aimed at agricultural applications.IMPORTANCEThe current scenario of climate change and desertification represents a series of incoming challenges for all living organisms. As the human population grows rapidly, so does the rising demand for food and natural resources; thus, it is necessary to make agriculture more efficient by optimizing soil and water usage, thus ensuring future food supplies. Particularly, the Atacama Desert (northern Chile) is considered the most arid place on Earth as a consequence of geological and climatic characteristics, such as the naturally low precipitation patterns and high temperatures, which makes it an ideal place to carry out research that seeks to aid agriculture in future conditions that are predicted to resemble these scenarios. Our main interest lies in utilizing microorganism consortia from plants thriving under extreme conditions, aiming to promote plant growth, improve crops, and render "unsuitable" soils farmable.

Insights into Regulation of C2 and C4 Photosynthesis in Amaranthaceae/Chenopodiaceae Using RNA-Seq.

Amaranthaceae (incl. Chenopodiaceae) shows an immense diversity of C4 syndromes. More than 15 independent origins of C4 photosynthesis, and the largest number of C4 species in eudicots signify the importance of this angiosperm lineage in C4 evolution. Here, we conduct RNA-Seq followed by comparative transcriptome analysis of three species from Camphorosmeae representing related clades with different photosynthetic types: Threlkeldia diffusa (C3), Sedobassia sedoides (C2), and Bassia prostrata (C4). Results show that B. prostrata belongs to the NADP-ME type and core genes encoding for C4 cycle are significantly upregulated when compared with Sed. sedoides and T. diffusa. Sedobassia sedoides and B. prostrata share a number of upregulated C4-related genes; however, two C4 transporters (DIT and TPT) are found significantly upregulated only in Sed. sedoides. Combined analysis of transcription factors (TFs) of the closely related lineages (Camphorosmeae and Salsoleae) revealed that no C3-specific TFs are higher in C2 species compared with C4 species; instead, the C2 species show their own set of upregulated TFs. Taken together, our study indicates that the hypothesis of the C2 photosynthesis as a proxy towards C4 photosynthesis is questionable in Sed. sedoides and more in favour of an independent evolutionary stable state.

The toxicity of selenium and mercury in Suaeda salsa after 7-days exposure.

Mercury is one of the major pollutants in the ocean, selenium causes toxicity beyond a certain limit, but there are few comparative toxic studies between them in halophytes. The study was to investigate the toxic effects of selenium (Se4+) and mercury (Hg2+) in halophyte Suaeda salsa at the level of genes, proteins and metabolites after exposure for 7 days. By integrating the results of proteomics and metabolomics, the pathway changed under different treatments were revealed. In Se4+-treated group, the changed 3 proteins and 10 metabolites participated in the process of substance metabolism (amino acid, pyrimidine), citrate cycle, pentose phosphate pathway, photosynthesis, energy, and protein biosynthesis. In Hg2+-treated group, the changed 10 proteins and 10 metabolites were related to photosynthesis, glycolysis, substance metabolism (cysteine and methionine, amino acid, pyrimidine), ATP synthesis and binding, tolerance, sugar-phosphatase activity, and citrate cycle. In Se4++ Hg2+-treated group, the changed 5 proteins an 12 metabolites involved in stress defence, iron ion binding, mitochondrial respiratory chain, structural constituent of ribosome, citrate cycle, and amino acid metabolism. Furthermore, the separate and combined selenium and mercury both inhibited growth of S. salsa, enhanced activity of antioxidant enzymes (superoxide dismutase, peroxidase and catalase), and disturbed osmotic regulation through the genes of choline monoxygenase and betaine aldehyde dehydrogenase. Our experiments also showed selenium could induce synergistic effects in S. salsa. In all, we successfully characterized the effects of selenium and mercury in plant which was helpful to evaluate the toxicity and interaction of marine pollutants.

Effect of irrigation salinity and ecotype on the growth, physiological indicators and seed yield and quality of Salicornia europaea.

The euhalophyte species Salicornia europaea is cultivated for oilseed and as a fodder crop in various parts of the world. In saline coastal environments it possesses great potential for the subsistence of the most disadvantaged farmers. We investigated the effect of salinity levels in irrigation water on the germination capacity, shoot biomass and seed productivity as well as diverse quality traits (nitrogen content in shoots and seeds and fatty acids, in seeds) and physiological traits (stable carbon and nitrogen isotopes and ion content) of two accessions collected in the United Arab Emirates (UAE). The three salinity levels tested were irrigation with fresh water (0.3 dS m-1), brackish water (25 dS m-1) and sea water (40 dS m-1). In addition, a hypersaline condition (80 dS m-1) was also tested for germination. The best germination rates were achieved with seeds exposed to fresh and brackish water, while imbibition with sea water decreased germination by half and hypersaline water inhibited it almost totally. However, the best irrigation regime in terms of biomass and seed yield involved brackish water. Moreover, rising salinity in the irrigation increased the stable isotope composition of carbon (δ13C) and nitrogen (δ15N), together with the Na+ and K+ of shoots and seeds, and the lipid levels of seeds, while the total nitrogen content and the profile of major fatty acids of seeds did not change. Differences between the two ecotypes existed for growth and seed yield with the best ecotype exhibiting lower δ13C and higher K+ in both shoots and seeds, lower Na+ and higher δ15N in shoots, and lower N in seeds, together with differences in major fatty acids. Physiological mechanisms behind the response to irrigation salinity and the ecotypic differences are discussed in terms of photosynthetic carbon and nitrogen metabolism.

A comparative metabolomics analysis of the halophyte Suaeda salsa and Salicornia europaea.

Suaeda salsa and Salicornia europaea are both annual herbaceous species belonging to the Chenopodiaceae family, and often grow together through our observations in the Yellow River Delta Nature Reserve, and could be used as raw material to produce food and beverages in food industry due to its high nutritional value. In this study, we adopted widely targeted metabolomics to identify 822 and 694 metabolites in the leaves of S. salsa and S. europaea, respectively, to provide a basic data for the future development and utilization of these two species. We found that these two plants were rich in metabolic components with high medical value, such as flavonoids, alkaloids and coumarins. The high contents of branched chain amino acid in these two species may be an important factor for their adaptation to saline-alkali environments. In addition, the contents of glucosamine (FC = 7.70), maltose (FC = 9.34) and D-(+)-sucrose (FC = 7.19) increased significantly, and the contents of D-(+)-glucose, 2-propenyl (sinigrin) and fructose 1-phosphate were significantly increased in the leaves of S. salsa compared to S. europaea, indicating that some certain compounds in different plants have different sensitivity to salt stress. Our work provides new perspectives about important second metabolism pathways in salt tolerance between these two plants, which could be helpful for studying the tolerance mechanisms of wetland plants.

Tides affect plant connectivity in coastal wetlands on a small-patch scale.

Coastal wetlands are ecologically and economically important; however, they are currently faced with fragmentation and loss. Plants are a fundamental element of wetlands and previous researches have focused on wetland plant connectivity; however, these researches have been conducted at the landscape but not species level. Here, given that tidal flats are important areas in coastal wetlands, we investigated the connectivity characteristics of typical plant species and environmental factors in different wetland regions influenced by various tidal conditions to reveal vegetation connectivity and its relationship with environmental factors on a small-patch scale. We found that tides negatively affect plant connectivity because both the Tamarix chinensis and Suaeda salsa have the highest connectivity on river banks, which are not influenced by tides. Of two tidal regions, different tides conditions have different influence on two plant species. T. chinensis had higher connectivity in the supratidal zone, whereas S. salsa had higher connectivity in the intertidal zone. Besides, the soil water content and soil salinity were significantly different in the three regions, but the soil total nitrogen and phosphorous were not. Soil water content and soil salinity were two factors that significantly affected plant connectivity. Specifically, soil water content positively affected the connectivity of T. chinensis and S. salsa, whereas soil salinity negatively affected the connectivity of T. chinensis. Taken together, these results indicate that tidal conditions affect plant connectivity on a small-patch scale. River banks and supratidal zone are beneficial for the recovery and growth of T. chinensis, intertidal zone and river banks are more conducive to the recovery and growth of S. salsa. Based on the above research, this study provides insights that could be applied to vegetation restoration in coastal wetlands.

Image and fractal analysis as a tool for evaluating salinity growth response between two Salicornia europaea populations.

BACKGROUND: This study describes a promising method for understanding how halophytes adapt to extreme saline conditions and to identify populations with greater resistance. Image and colour analyses have the ability to obtain many image parameters and to discriminate between different aspects in plants, which makes them a suitable tool in combination with genetic analysis to study the plants salt tolerance. To the best of our knowledge, there are no publications about the monitoring of halophytic plants by non-destructive methods for identifying the differences between plants that belong to different maternal salinity environments. The aim is to evaluate the ability of image analysis as a non-destructive method and principal component analysis (PCA) to identify the multiple responses of two S. europaea populations, and to determine which population is most affected by different salinity treatments as a preliminary model of selection. RESULTS: Image analysis was beneficial for detecting the phenotypic variability of two S. europaea populations by morphometric and colour parameters, fractal dimension (FD), projected area (A), shoot height (H), number of branches (B), shoot diameter (S) and colour change (ΔE). S was found to strongly positively correlate with both proline content and ΔE, and negatively with chlorophyll content. These results suggest that proline and ΔE are strongly linked to plant succulence, while chlorophyll decreases with increased succulence. The negative correlation between FD and hydrogen peroxide (HP) suggests that when the plant is under salt stress, HP content increases in plants causing a reduction in plant complexity and foliage growth. The PCA results indicate that the greater the stress, the more marked the differences. At 400 mM a shorter distance between the factorial scores was observed. Genetic variability analysis provided evidence of the differences between these populations. CONCLUSIONS: Our non-destructive method is beneficial for evaluating the halophyte development under salt stress. FD, S and ΔE were relevant indicators of plant architecture. PCA provided evidence that anthropogenic saline plants were more tolerant to saline stress. Furthermore, random amplified polymorphic DNA analysis provided a quick method for determining genetic variation patterns between the two populations and provided evidence of genetic differences between them.

Salinity relief aniline induced oxidative stress in Suaeda salsa: Activities of antioxidative enzyme and EPR measurements.

Wastewater from printing and dyeing processes often contains aniline and high salinity, which are hazardous to aquatic species. Glycophytic plants cannot survive under high-salinity conditions, whereas halophytes grow well in such an environment. In this study, we investigated the influence of NaCl on the antioxidant level in Suaeda salsa affected by aniline stress. The seedlings showed various growth toxicity effects under different concentrations of aniline. The results showed that the effect of the aniline was more severe for the root growth compared to that for the shoot growth. Aniline exposure significantly increased the total free radicals and ·OH radicals in the plants. Suaeda salsa exposure to aniline caused oxidative stress by altering the superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activity, which resulted in the overproduction of H2O2 and the inducement of lipid peroxidation. Analysis revealed that the malondialdehyde (MDA) content was enhanced after aniline exposure and that the chlorophyll content was significantly decreased. The results showed that aniline induced the production of free radicals and reactive oxygen species (ROS), and changed the antioxidant defense system. This ultimately resulted in oxidative damage in S. salsa; however, it was found that moderate salinity could mitigate the effects. In conclusion, salinity may alleviate the growth inhibition caused by aniline by regulating the antioxidant capacity of S. salsa.

Wild vs cultivated halophytes: Nutritional and functional differences.

Some halophyte plants are currently used in gourmet cuisine due to their unique organoleptic properties. Moreover, they exhibit excellent nutritional and functional properties, being rich in polyphenolics and vitamins. These compounds are associated to strong antioxidant activity and enhanced health benefits. This work compared the nutritional properties and antioxidant potential of three species (Mesembryanthemum nodiflorum, Suaeda maritima and Sarcocornia fruticosa) collected in saltmarshes from Portugal and Spain with those of cultivated plants. The latter were generally more succulent and had higher contents of minerals than plants obtained from the wild and contained less fibre. All species assayed are a good source of proteins, fibres and minerals. Additionally, they are good sources of carotenoids and vitamins A, C and B6 and showed good antioxidant potential particularly S. maritima. Chromatographic analysis of the phenolic profile revealed that ferulic and caffeic acids as the most relevant phenolic compounds detected in the halophytes tested.

Influence of cultivation salinity in the nutritional composition, antioxidant capacity and microbial quality of Salicornia ramosissima commercially produced in soilless systems.

The consumption of halophytes as healthy gourmet food has increased considerably in the past few years. However, knowledge on the nutritional profile of domesticated halophytes is scarce and little is known on which cultivation conditions can produce plants with the best nutritional and functional properties. In this context, Salicornia ramosissima J. Woods was cultivated in six different salt concentrations, ranging from 35 to 465 mM of NaCl. Both the nutritional profile, the antioxidant capacity, and microbial quality of the produced plants were evaluated including minerals and vitamins. Salt has a marked effect on growth, which decreases for salinities higher than 110 mM. Nonetheless, plants cultivated with intermediate levels of salinity (110 and 200 mM) revealed better antioxidant status with higher amounts of phenolic compounds. Overall, results from this paper indicated that soilless culture systems using low-intermediate salinities produces S. ramosissima plants fit for commercialization and human consumption.

Phenotypic plasticity in diaspore production of a amphi-basicarpic cold desert annual that produces polymorphic diaspores.

Phenotypic plasticity has been studied in diaspore-dimorphic species, but no such study has been done on a diaspore-polymorphic species. Our aim was to determine the effects of abiotic and biotic factors on phenotypic plasticity of the diaspore-polymorphic cold desert annual Ceratocarpus arenarius. Plants produced from dispersal units near the soil surface (a, basicarps) and at the middle (c) and upper (f) parts of the plant canopy were subjected to different levels of soil moisture, nutrient supply and intramorph and intermorph densities. Different levels of these biotic and abiotic factors resulted in significant variation in total plant mass, diaspore mass, mass allocation to stem and reproductive organs and total number and proportion of morphs a, c and f on an individual. The effect of stress on number and mass of a dispersal unit morph varied by treatment, with dispersal unit f having the highest CV and dispersal unit a the lowest. The success of this diaspore polymorphic species in its rainfall-unpredictable environment likely is enhanced by plasticity in production of the different types of diaspores.

Aquaponics using a fish farm effluent shifts bacterial communities profile in halophytes rhizosphere and endosphere.

The intensification of marine aquaculture raises multiple sustainability issues, namely the handling of nutrient-rich effluents that can adversely impact ecosystems. As integrated multi-trophic aquaculture (IMTA) gains momentum, the use of halophyte plants to phytoremediate aquaculture effluents has received growing attention, particularly in aquaponics. It is, therefore, important to obtain a more in-depth knowledge of the microbial communities present in the root systems of these plants, both in their natural environment (sediment) and in aquaponics, in order to understand their nutrient removal potential. The present study used denaturing gradient gel electrophoresis (DGGE) and barcoded pyrosequencing to assess the bacterial community present in the endosphere and rhizosphere of three halophyte plants: Halimione portulacoides, Salicornia ramosissima and Sarcocornia perennis. Species-specific effects were recorded in the profile and diversity of the bacterial communities present in halophyte roots, with significant differences also recorded for the same halophyte species grown in contrasting environments (sediment vs. aquaponics). In aquaponics the most abundant groups belonged to the orders Rhodocyclales, Campylobacterales, Rhodobacterales and Desulfobacterales, while in the natural environment (sediment) the most abundant groups belonged to the orders Rhizobiales, Sphingomonadales and Alteromonadales. An overall enrichment in bacterial taxa involved in nutrient cycling was recorded in the roots of halophytes grown in aquaponics (such as Denitromonas, Mesorhizobium, Colwellia, Dokdonella and Arcobacter), thereby highlighting their potential to reduce the nutrient loads from aquaculture effluents.

Transcriptome Profiling of Haloxylon persicum (Bunge ex Boiss and Buhse) an Endangered Plant Species under PEG-Induced Drought Stress.

Haloxylon persicum is an endangered western Asiatic desert plant species, which survives under extreme environmental conditions. In this study, we focused on transcriptome analysis of H. persicum to understand the molecular mechanisms associated with drought tolerance. Two different periods of polyethylene glycol (PEG)-induced drought stress (48 h and 72 h) were imposed on H. persicum under in vitro conditions, which resulted in 18 million reads, subsequently assembled by de novo method with more than 8000 transcripts in each treatment. The N50 values were 1437, 1467, and 1524 for the control sample, 48 h samples, and 72 h samples, respectively. The gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis resulted in enrichment of mitogen-activated protein kinase (MAPK) and plant hormone signal transduction pathways under PEG-induced drought conditions. The differential gene expression analysis (DGEs) revealed significant changes in the expression pattern between the control and the treated samples. The KEGG analysis resulted in mapping transcripts with 138 different pathways reported in plants. The differential expression of drought-responsive transcription factors depicts the possible signaling cascades involved in drought tolerance. The present study provides greater insight into the fundamental transcriptome reprogramming of desert plants under drought.

Different effects of NaCl and Na2SO4 on soil net nitrogen mineralization in coastal wetlands.

NaCl and Na2SO4 are the foremost salt compositions in coastal wetlands, while their effects on soil net nitrogen mineralization still remain unclear. Aimed at investigating the two salt compositions on soil net nitrogen mineralization, a 30-day laboratory incubation experiment was respectively conducted by adding 5‰ NaCl and Na2SO4 to incubated coastal wetland soils under aerobic conditions. Our results showed that Na2SO4 addition increased the rates of mineralization (Rmin) by an average of 33.03% and nitrification (Rnit) by 23.84% during the incubation (p < 0.05). In contrast, NaCl addition significantly reduced Rmin by 71% and Rnit by 44% at day 7 (p < 0.05). The activities of fluorescein diacetate, arylamidase and urease in Na2SO4 addition treatments were higher than those in NaCl addition treatment. These results demonstrated the ion-specific effects of salt type on nitrogen mineralization rates and enzyme activities.

Total and Methylmercury of Suaeda heteroptera Wetland Soil Response to a Salinity Gradient Under Wetting and Drying Conditions.

Mercury (Hg) methylation could occur in freshwater ecosystems with low or high salinity. However, few studies are available about the effects of salinity change on mercury(Hg) release and methylation. In-situ experiments using Suaeda heteroptera wetland soil column from the Liaohe estuary were performed to decipher how total mercury (THg) and methylmercury (MeHg) contents change under fluctuant salinity and wet and dry soil conditions. Salinity gradients were set to 0.50% (S1), 1.00% (S2), 1.50% (S3) and 1.80% (S4), and pure deionized water was used as a blank control (CK). Wet and dry soil conditions were set to full inundation condition (WD1) and naturally dried treatment (WD2). Results indicated that the highest THg and MeHg contents were found in surface and bottom soil when water salinity treatment was CK under WD1. THg and MeHg decreased with salinity under WD1. THg contents in overlying water varied from 0.854 to 1.243 µg L-1 under WD1 treatments and increased with salinity change. When under WD2 treatment, THg contents in both soil layers gradually decreased with rising salinity. Meanwhile, MeHg contents in both soil layers reached the lowest level at CK (1.666 µg kg-1and 2.520 µg kg-1) and increased gradually with the rising salinity. By comparison, THg content of the soil was much lower in WD1 than that in WD2. Under the WD1 condition, the MeHg contents and %MeHg decreased with rising salinity and showed significantly different in different salinity treatment, however, its showed an opposite trend with rising salinity under the WD2 condition.

Nutrient availability affects the polar lipidome of Halimione portulacoides leaves cultured in hydroponics.

Halophytes are increasingly regarded as suitable extractive species and co-products for coastal Integrated Multi-Trophic Aquaculture (IMTA) and studying their lipidome is a valid means towards their economic valorization. Halimione portulacoides (L.) Aellen edible leaves are rich in functional lipids with nutraceutical and pharmaceutical relevance and the present study aimed to investigate the extent to which its lipidome remains unchanged under a range of dissolved inorganic nitrogen (N) and phosphorus (P) concentrations typical of aquaculture effluents. Lipidomics analysis, done by hydrophilic interaction liquid chromatography coupled to high resolution mass spectrometry, identified 175 lipid species in the lipid extract of leaves: 140 phospholipids (PLs) and 35 glycolipids (GLs). Plants irrigated with a saline solution with 20-100 mg DIN-N L-1 and 3-15.5 mg DIP-P L-1 under a 1-week hydraulic retention time displayed a relatively stable lipidome. At lower concentrations (6 mg DIN-N L-1 and 0.8 mg DIP-P L-1), plants exhibited less PLs and GLs per unit of leaves dry weight and the GLs fraction of the lipidome changed significantly. This study reveals the importance of analyzing the lipidomic profile of halophytes under different nutritional regimens in order to establish nutrient-limitation thresholds and assure production conditions that deliver a final product with a consistent lipid profile.

Mining the roots of various species of the halophyte Suaeda for halotolerant nitrogen-fixing endophytic bacteria with the potential for promoting plant growth.

Saline area may tend to be a productive land; however, many of salt-affected soils have nitrogen limitation and depend on plant-associated diazotrophs as their source of 'new' nitrogen. Herein, a total of 316 salinity tolerant nitrogen-fixing endophytic bacteria were isolated from roots of the halophyte Suaeda sp. sampled from 22 different areas of Iran to prepare the collection of nitrogen-fixing bacterial endophytes and evaluate the plant growth-promoting effect of effective isolates on growth of the halophyte Suaeda maritima. All of the identified nitrogen-fixing endophytes were classified to Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes phylum while we did not detect common nitrogen-fixing endophyte of glycophytes like Azospirillum. The genera Pseudomonas and Microbacterium were both encountered in high abundance in all samples, indicating that they might play an advanced role in the micro-ecosystem of the halophyte Suaeda. In addition, the results also showed that not only soil salinity can affect halophyte endophytic composition but also other factors such as geographical location, plant species, and other soil properties may be involved. Interestingly, only Zhihengliuella halotolerans and Brachybacterium sp. belonging to Actinobacteria could grow in semi-solid N-free (NFb) medium supplemented with 6% NaCl and highly enhanced growth of S. maritima in vitro. Overall, this study offers useful new resources for nitrogen-fixing endophytic bacteria which may be utilized to improve approaches for providing bio-fertilizer useful in saline-based agriculture.

Aquaponic System with White Shrimp Litopenaeus vannamei Rearing and Production of the Plants Batis maritima, Sarcocornia neei and Sporobolus virginicus

Abstract Aquaponics is a system that integrates aquaculture with plant production in which two species are benefited, and there is water saving. In this study was carried out with an aquaponic system to verify the interaction between the growth of the halophytes Batis maritime, Sarcocornia neei, and Sporobolus virginicus associated with white shrimp Litopenaeus vannamei rearing. We also investigated if there were different responses of physicochemical variables of the water in the experimental shrimp culture ponds integrated into the growth of plants and control ponds, without plants, throughout a 56-day period. The treatment experiment and control presented a statistically significant difference in total dissolved solids, salinity, total suspended solids, ammonia, orthophosphate, and nitrite. In the experimental treatment, with the presence of plants and recirculating water, a reduction of total suspended solids, ammonia and orthophosphate was observed. The rate of shrimp production was not significantly different between treatments, and the performance was similar to that of other studies. The biomass gain of the halophyte B. maritima was 876.6 grams in 0.5 m² and of S. neei was 48.8 grams in 0.16 m². All plants of the species S. virginicus died during the experiment.

CO2 uptake and chlorophyll a fluorescence of Suaeda fruticosa grown under diurnal rhythm and after transfer to continuous dark.

Although only 2-4% of absorbed light is emitted as chlorophyll (Chl) a fluorescence, its measurement provides valuable information on photosynthesis of the plant, particularly of Photosystem II (PSII) and Photosystem I (PSI). In this paper, we have examined photosynthetic parameters of Suaeda fruticosa L. (family: Amaranthaceae), surviving under extreme xerohalophytic conditions, as influenced by diurnal rhythm or continuous dark condition. We report here CO2 gas exchange and the kinetics of Chl a fluorescence of S. fruticosa, made every 3 hours (hrs) for 3 days, using a portable infra-red gas analyzer and a Handy PEA fluorimeter. Our measurements on CO2 gas exchange show the maximum rate of photosynthesis to be at 08:00 hrs under diurnal condition and at 05:00 hrs under continuous dark. From the OJIP phase of Chl a fluorescence transient, we have inferred that the maximum quantum yield of PSII photochemistry must have increased during the night under diurnal rhythm, and between 11:00 and 17:00 hrs under constant dark. Overall, our study has revealed novel insights into how photosynthetic reactions are affected by the photoperiodic cycles in S. fruticosa under high salinity. This study has further revealed a unique strategy operating in this xero-halophyte where the repair mechanism for damaged PSII operates during the dark, which, we suggest, contributes to its ecological adaptation and ability to survive and reproduce under extreme saline, high light, and drought conditions. We expect these investigations to help in identifying key genes and pathways for raising crops for saline and dry areas.

Salinity-induced alterations in plant growth, antioxidant enzyme activities, and lead transportation and accumulation in Suaeda salsa: implications for phytoremediation.

Halophytes have been considered promising candidates for accumulating heavy metals from saline soils; however, little information has been given on plant physiological responses and heavy metal transportation and accumulation in halophytes that grow in heavy metal-polluted saline soils. This study hypothesized that salinity or heavy metals could induce alterations in plant growth, antioxidant enzyme activities and accumulation and transportation of heavy metals or sodium (Na) in Suaeda salsa. Pot experiments were conducted to test the above hypothesis. Lead (Pb) was selected as the representative heavy metal, and NaCl was added to simulate the Pb-polluted saline soil. The results showed that 0.5% NaCl addition alleviated the inhibition of plant growth under moderate Pb stress (35 and 100 mg kg-1 Pb levels), while the phytotoxicity on plants was magnified by 1.0% NaCl addition. NaCl weakened the oxidative stress in Pb-treated plants by increasing the activity levels of antioxidative enzymes (dismutase (SOD), peroxidase (POD) and catalase (CAT)). At all Pb levels, as the NaCl addition increased, significant increases were observed in the concentration of Na. The 100 mg kg-1 Pb induced a greater increase in Na concentrations than the 35 mg kg-1 Pb did, while the latter induced a greater increase than the 300 mg kg-1 Pb did. NaCl improved Pb translocation factor and its accumulation in Suaeda salsa under Pb stress, indicating that NaCl improves Pb uptake and translocation from roots to shoots and enhances the phytoextraction of Pb. Compared with the 0.1% NaCl treatment, the 0.5 and 1.0% NaCl treatments increased the concentrations of bioavailable Pb in the rhizosphere by 15.0-19.2 and 28.6-35.1%, respectively, indicating the contribution of salinity in producing more available Pb for plant uptake. Moderate salinity may be profitable for Pb transportation and accumulation in plants when there are positive effects on plant growth, antioxidant enzyme activities and Pb availability. These facts suggest that the halophyte Suaeda salsa may be exploited to remediate heavy metal-contaminated saline soils.