Salinity Stress Treatments Research Articles

Biochemical, physiological and phenological genetic analysis in common bean (Phaseolus vulgaris L.) under salt stress

Salinity is one of the most important abiotic stresses affecting agricultural productivity. The present study investigated combining abilities, heterosis and heritability estimates of common bean under salinity conditions for biochemical, physiological and phenological traits using a half-diallel cross. The salinity stress treatments were applied during all the vegetative cycle. Genetic analysis revealed highly significant genotypic variations between the four parents and their six hybrids, indicating a genetic variability and possibility of genetic improvement using such genetic material of common bean for salinity tolerance. Both general (GCA) and specific (SCA) combining abilities were highly significant for all the studied traits under all conditions, revealing the important role of both additive and dominant gene effects in the inheritance of these traits. The ratio GCA/SCA indicated preponderance of the additive effects for all the studied characters. The parental genotypes Améliore Roza and Coco nain proved to be the best combiners for salinity tolerance; on the other hand the crosses namely Amina × Améliore Roza; MGT × Améliore Roza and Coco nain × Amina recorded significant heterosis percentage relative to mid-parent (MP) and better parent (BP) for almost all the traits, the same crosses recorded significantly positive SCA effects. Diallel analysis revealed high heritability in broad-sense for salinity tolerance, while moderate to high narrow-sense heritability suggests a large breeding population and possible selection for salt tolerance. The results of this study confirmed that salinity tolerance is expressed by a different set of genes that could be pyramided using different genotypes to enhance salinity tolerance.

Pearl millet stress-responsive NAC transcription factor PgNAC21 enhances salinity stress tolerance in Arabidopsis

Pearl millet (Pennisetum glaucum) is the sixth-leading cereal crop and a staple food crop. It is known for its high tolerance to abiotic stress and good nutrient profile. NAC (NAM, ATAF1/2 and CUC) transcription factors (TFs) play an important role in abiotic stress tolerance. In our study, the pearl millet stress-responsive NAC TF gene PgNAC21 was characterized. Gene expression analysis revealed that PgNAC21 expression is induced by salinity stress and abscisic acid (ABA) treatment. In silico promoter analysis showed the presence of ABA response elements (ABREs) and MYB TF binding sites. A yeast one-hybrid assay indicated that a putative MYB TF in pearl millet, PgMYB1, binds to the promoter of PgNAC21. A transactivation assay in yeast cells revealed that PgNAC21 functions as a transcription activator and that its activation domain is located in its C-terminus. Relative to control plants, Arabidopsis plants overexpressing PgNAC21 exhibited better seed germination, heavier fresh weight and greater root length under salinity stress. Overexpression of PgNAC21 in Arabidopsis plants also enhanced the expression of stress-responsive genes such as GSTF6 (GLUTATHIONE S-TRANSFERASE 6), COR47 (COLD-REGULATED 47) and RD20 (RESPONSIVE TO DEHYDRATION 20). Our data demonstrate that PgNAC21 functions as a stress-responsive NAC TF and can be utilized in transgenic approaches for developing salinity stress tolerance in crop plants.

Increased salt and drought tolerance by D-pinitol production in transgenic Arabidopsis thaliana

D-ononitol epimerase (OEP) catalyzes the conversion of D-ononitol to D-pinitol, which is the last step in the biosynthetic pathway, where myo-inositol is converted to pinitol in higher plants. In this study, OEP cDNA was isolated from Glycine max (GmOEP) and was functionally characterized, which confirmed that GmOEP expression was induced by high salinity and drought stress treatments. To understand the biological function of GmOEP, transgenic Arabidopsis plants overexpressing this protein were constructed. The transgenic Arabidopsis plants displayed enhanced tolerance to high salinity and drought stress treatments.

Morpho-anatomy and physiology of red galangal (Alpinia purpurata) and white galangal (Alpinia galanga) under some salinity stress levels

Setiawati T, Susilawati A, Mutaqin AZ, Nurzaman M, Annisa, Partasasmita R, Karyono. 2018. Morpho-anatomy and physiology of red galangal (Alpinia purpurata) and white galangal (Alpinia galanga) under some salinity stress levels. Biodiversitas 19: 809-815. Soil salinity is one of the most urgent issues in agriculture as it can reduce plant growth and productivity. Efforts on development of galangal plant on saline soils are still encountering some obstacles such as lack of information on the galangal types that are tolerant to saline condition. The purpose of this study was to determine morpho-anatomical and physiological responses of red galangal (Alpinia purpurata (Vieill.) K. Schum.) and white galangal (Alpinia galanga (L.) Willd.) to salinity stress treatments. This research used a Randomized Block Design (RBD) assigned in a factorial treatment design of two factors, i.e., (i) species of galangal consisting of two levels i.e., red galangal and white galangal, (ii) NaCl concentration consisting of five levels, i.e., 0‰, 3‰, 6‰, 9‰ and 12‰. Each treatment was three replicates. Observation was done on the growth parameters when the plants showed wilting symptoms. The observed data were subjected to Analysis of Variance (ANOVA), followed by a post hoc Duncan Multiple Range Test (DMRT) at α 5% when the treatment effect was significant. The results showed that salinity stress treatment significantly reduced the plant height increase, leaf area, dry weight, stomata density, chlorophyll content and increased thickness of root epidermis, and proline content in both species of galangal. Red galangal was more tolerant than white galangal.

Initial Growth and Gas Exchanges of Plants of Colored Cotton Submitted to Saline Stress

The objective of the research was to evaluate the effects of saline stress on the initial growth and physiological parameters of three varieties of cotton plants, being two cultivars of colored fiber (BRS Topazio and BRS Verde) and one of white fiber (BRS 286). The experiment was conducted under greenhouse conditions. After chemical depletion with sulfuric acid, five seeds were seeded in polyethylene pots of 20 kg, leaving only one plant per pot after thinning. The experimental design was completely randomized, with a factorial scheme of 3 × 5, with five replications, totaling 75 plots, being three cotton varieties and five saline stress treatments—1.1; 3.1; 5.1; 7.1; 9.1 dS m−1. The evaluations occurred at 15 and 30 days after the beginning of the treatments (DAT) for growth variables (plant height, stem diameter, number of leaves and leaf area) and gas exchange (stomatal conductance, net photosynthesis rate and transpiration. The variety that was most resistant to the salt stress levels studied was BRS 286, followed by BRS Topazio and BRS Verde.

Salinity reduces 2,4-D efficacy in Echinochloa crusgalli by affecting redox balance, nutrient acquisition, and hormonal regulation.

Distinct salinity levels have been reported to enhance plants tolerance to different types of stresses. The aim of this research is to assess the interaction of saline stress and the use of 2,4-D as a means of controlling the growth of Echinochloa crusgalli. The resultant effect of such interaction is vital for a sustainable approach of weed management and food production. The results showed that 2,4-D alone treatment reduces the chlorophyll contents, photosynthetic capacity, enhanced MDA, electrolyte leakage, and ROS production (H2O2, O2·-) and inhibited the activities of ROS scavenging enzymes. Further analysis of the ultrastructure of chloroplasts indicated that 2,4-D induced severe damage to the ultrastructure of chloroplasts and thylakoids. Severe saline stress (8dSm-1) followed by mild saline stress treatments (4dSm-1) also reduced the E. crusgalli growth, but had the least impact as compared to the 2,4-D alone treatment. Surprisingly, under combined treatments (salinity + 2,4-D), the phytotoxic effect of 2,4-D was reduced on saline-stressed E. crusgalli plants, especially under mild saline + 2,4-D treatment. This stimulated growth of E. crusgalli is related to the higher activities of enzymatic and non-enzymatic antioxidants and dynamic regulation of IAA, ABA under mild saline + 2,4-D treatment. This shows that 2,4-D efficacy was affected by salinity in a stress intensity-dependent manner, which may result in the need for greater herbicide application rates, additional application times, or more weed control operations required for controlling salt-affected weed.

Genome-wide identification, classification and expression analysis of NAC family of genes in sorghum [Sorghum bicolor (L.) Moench

NAC transcription factors are involved in many biological processes via regulation of downstream target gene expression and play essential roles in regulation of plant growth and improving plant tolerance to abiotic stress. NAC transcription factors have been studied in various species, but little information is available regarding these factors in sorghum. Genome-wide investigation of potentially abiotic stress related sorghum NAC-type genes was performed. A total of 145 non-redundant NAC genes (SbNAC1 –SbNAC145) were identified in the sorghum genome. These genes were distributed unevenly across the 10 chromosomes, and were divided into 16 groups based on sequence similarity. Gene structure analysis indicated that most SbNAC genes contained three exons and two introns, and had ten putative conserved motifs. Phylogenetic analysis indicated that the SbNAC genes with similar motif distributions were clustered into the same branch. Seven SbNAC genes, which were grouped into the stress-related subgroup, were isolated and have been confirmed to have transcriptional activity in yeast. SbNAC genes showed differential expression patterns over time in response to dehydration, salinity, cold, and phytohormone abscisic acid stress treatments, thus suggesting essential roles in plant responses to abiotic stress. In the germination stage, SbNAC56 overexpression transgenic lines exhibited significantly enhanced hypersensitivities to ABA, NaCl and d-Mannitol. This may infer that SbNAC56 may play essential roles in plants response to abiotic stresses in ABA dependent signaling pathway. Here, we present a comprehensive overview of the SbNAC genes and provide a foundation for future functional research regarding their biological roles in sorghum stress tolerance, even in the regulation of plant growth.

Effects of Salinity Stress at Different Growth Stages on Tomato Growth, Yield, and Water-Use Efficiency

ABSTRACTThis study investigated the effects of salinity stress at different growth stages on the growth, yield, fruit quality, and water-use efficiency (WUE) of tomato (Solanum lycopersicum) plants cultivated under soilless conditions. Six different growth stages were exposed to the same salinity stress treatments using a completely randomized design, with three pots (six plants) per treatment. It was found that short-term (<21 days) salinity stress during any of the growth stages did not affect tomato growth or WUE, and during the vegetative stage did not affect yield. Salinity stress during the flowering and fruiting stages caused a reduction in tomato yield, which was due to a reduction in the number of fruit produced rather than the fruit size. However, salt exposure at the fruiting stage also improved fruit quality. The effect of salinity stress on the yield and fruit quality of the frontal and later truss depended on the developmental stage of the truss at the time when the stress occurred.

RNA-seq analysis reveals the role of a small GTP-binding protein, Rab7, in regulating clathrin-mediated endocytosis and salinity-stress resistance in peanut

Small GTP-binding proteins, Rab7, are known to be responsive to abiotic stresses in plants, but the molecular mechanism is poorly understood. To investigate how AhRab7 increases resistance to salinity stress in peanut, this study compared a transgenic genotype (S5) that overexpressed the AhRab7 gene and that had high salinity resistance with a non-transgenic genotype (S7) that had low salinity resistance. Digital gene expression (DGE) sequencing was performed with leaves of S5 and S7 before and after salinity-stress treatment. In total, 2697 differentially expressed genes (DEGs) were identified between S5 and S7, and KEGG enrichment analyses showed that the DEGs are involved pathways including endocytosis, lysosome, hormone signaling, phosphatidylinositol signaling, calcium, and others. Among them, 164 were differentially regulated after salinity-stress treatment. Of 164 DEGs, 110 were responsive to salinity stress in S5 and/or S7. The 110 DEGs included genes that encode the following kinds of transcription factors and proteins known to be involved in resistance to salinity stress: WRKY, NAC, MYM-type zinc finger, late embryogenesis abundant proteins, lipid transfer protein, 1-cys peroxiredoxin, aquaporin, oleosin, and others. AhRab7 gene might mediate signaling pathways including phosphatidylinositol, calcium, abscisic acid, etc., and then regulate the expression of transcription factors and downstream genes for ROS scavenging in peanut. The results of this study will be useful for further investigations of the mechanism underlying the role of the AhRab7 gene in resistance to salinity stress in peanut.

Analyses of abiotic stress and brassinosteroid-related some genes in barley roots grown under salinity stress and HBR treatments: Expression profiles and phylogeny

We aimed to investigate abiotic stress (WAK, HvPIP1.1, HvPIP1.2, HvPIP1.3, HvPIP1.5, CYCD3, DREB2) and brassinosteroid-related gene (DWARF4) expressions in barley (Hordeum vulgare L. cv. “Hilal”) roots grown under different salt (150 and 250 mM), HBR (0.5 and 1 μM), and salt + HBR applications during 48 and 72 h at dark with their controls. Phylogenetic trees were also constructed to observe relationships among genes found in other plants. The expression of HvPIP1.2 and WAK reduced after salt treatment while HvPIP1.3, DREB2 and DWARF4 expressions increased. HvPIP1.1, HvPIP1.2, HvPIP1.3, HvPIP1.5 and DWARF4 expressions were upregulated under only HBR applications. Salt + HBR treatments increased HvPIP1.1, DREB2 and DWARF4 but decreased HvPIP1.2. Phylogenetic analyses indicated that Oryza sativa L. shared similar sequences with HvPIP1.5. CYCD3 could diverge relatively earlier from cyclin genes during evolution as it segregates in a distinct clade. Sorghum bicolor showed sequence homology with DREB2. Oryza australiensis L. and DWARF4 were found in the same clade. To our knowledge, this is the first detailed report related to salt stress and HBR applications in terms of the expression of different genes in barley, providing a valuable information for molecular breeding improvement of stress-related traits.

Digital expression analysis of the genes associated with salinity resistance after overexpression of a stress-responsive small GTP-binding RabG protein in peanut.

The Rab protein family is the largest family of the small GTP-binding proteins. Among them, the RabG genes are known to be responsive to abiotic stresses, but the molecular mechanisms of the stress responses mediated by RabG genes in plants is poorly understood. To investigate the molecular mechanism of AhRabG gene in peanut, transgenic plants overexpressing the AhRabG gene (S6) with relatively higher salinity resistance than the non-transgenic plants (S7) were obtained. Digital gene expression (DGE) sequencing was performed with the leaves of S6 and S7 plants before and after salinity-stress treatment. The AhRabG gene in peanut was found to be involved in a few pathways such as "photosynthesis", "oxidative phosphorylation", "AMPK signaling pathway", "plant hormone signal transduction", etc. A total of 298 differentially expressed genes (DEGs) were found to be upregulated or downregulated at five sampling time points based on the comparison between S6 and S7 plants. Among them, 132 DEGs were responsive to salinity stress in S6 and/or S7 after salinity-stress treatment. These 132 DEGs included genes encoding various transcription factors and proteins involved in resistance to salinity stress such as MYB, AP2, RING-H2 zinc finger proteins, late embryogenesis abundant (LEA) proteins, dehydration-responsive protein RD22, peroxidases, CBL-interacting protein kinases, calcium-binding proteins, and others. The information from this study will be useful for further studies on elucidating the mechanism of salinity resistance conferred by RabG genein peanut.

Cloning and characterization of a serine/threonine protein phosphatase2A-encoding gene IbPP2A1 from Ipomoea batatas (L.) Lam.

Sweet potato is one of the most important food crops with strong environmental adaptability. Protein phosphatase 2A (PP2A) is a major intracellular protein phosphatase that plays crucial roles in hormone signal transduction and abiotic stress response. Characterization of PP2A can elucidate the mechanisms of stress resistance in this crop. In this study, a total of 15 PP2A transcripts, including nine regulatory subunit-encoding sequences and six catalytic subunit-encoding sequences, were identified from sweet potato and found to be expressed at varying levels. Only one contained a complete open reading frame and encoded a B regulatory subunit (termed IbPP2A1). Ten polymorphic sites were distributed in the coding region of this gene, but most did not result in amino acid change. RNA sequencing-based digital gene expression profiling showed that this PP2A gene was primarily expressed in fibrous roots and developing tuberous roots under natural conditions. After drought, salinity, and alkaline stress treatment, the expression of IbPP2A1 was obviously upregulated in stems and tuberous roots at 2 days, whereas the expression of IbPP2A1 in leaves was only upregulated by drought stress at 2 days. However, heterogeneous expression of IbPP2A1 did not enhance abiotic stress tolerance in recombinant Saccharomyces cerevisiae. The results described here indicate that IbPP2A1 is an abiotic stress-responsive gene, but it could not work alone in vitro. This study provides a preliminary but global insight into PP2A proteins in sweet potato for further investigations on improving stress tolerance in this crop.

Photoprotective and antioxidative mechanisms against oxidative damage in Fargesia rufa subjected to drought and salinity.

Drought and salinity are the two most common and frequently co-occurring abiotic stresses limiting plant productivity worldwide, yet it remains unclear whether bamboo species possess effective mechanisms to protect against oxidative damage caused by drought and salinity, either alone or in combination. In this study, we utilised Fargesia rufa Yi, a species important to forest carbon sequestration and endangered giant pandas, to evaluate physiological, biochemical and ultrastructural responses to drought, salinity and their combination. Under drought alone, F. rufa exhibited reduced water loss from leaves, photochemistry inhibition, pigment degradation, reactive oxygen species accumulation, lipid peroxidation, and damage to organelles compared with salinity and combined stress treatments. The superior performance under drought alone was attributed to greater thermal dissipation and the water-water cycle capacities, increased SOD/AsA-GSH cycle enzymes activities, and a favourable redox balance of antioxidants. Therefore, relative to salinity alone and drought+salinity, F. rufa plants under drought exhibit highly efficient mechanisms to protect against oxidative damage, which most likely allow accelerated recovery of photosynthetic plasticity once the stress is removed.

Non-destructive Phenotyping of Lettuce Plants in Early Stages of Development with Optical Sensors.

Rapid development of plants is important for the production of ‘baby-leaf’ lettuce that is harvested when plants reach the four- to eight-leaf stage of growth. However, environmental factors, such as high or low temperature, or elevated concentrations of salt, inhibit lettuce growth. Therefore, non-destructive evaluations of plants can provide valuable information to breeders and growers. The objective of the present study was to test the feasibility of using non-destructive phenotyping with optical sensors for the evaluations of lettuce plants in early stages of development. We performed the series of experiments to determine if hyperspectral imaging and chlorophyll fluorescence imaging can determine phenotypic changes manifested on lettuce plants subjected to the extreme temperature and salinity stress treatments. Our results indicate that top view optical sensors alone can accurately determine plant size to approximately 7 g fresh weight. Hyperspectral imaging analysis was able to detect changes in the total chlorophyll (RCC) and anthocyanin (RAC) content, while chlorophyll fluorescence imaging revealed photoinhibition and reduction of plant growth caused by the extreme growing temperatures (3 and 39°C) and salinity (100 mM NaCl). Though no significant correlation was found between Fv/Fm and decrease in plant growth due to stress when comparisons were made across multiple accessions, our results indicate that lettuce plants have a high adaptability to both low (3°C) and high (39°C) temperatures, with no permanent damage to photosynthetic apparatus and fast recovery of plants after moving them to the optimal (21°C) temperature. We have also detected a strong relationship between visual rating of the green- and red-leaf color intensity and RCC and RAC, respectively. Differences in RAC among accessions suggest that the selection for intense red color may be easier to perform at somewhat lower than the optimal temperature. This study serves as a proof of concept that optical sensors can be successfully used as tools for breeders when evaluating young lettuce plants. Moreover, we were able to identify the locus for light green leaf color (qLG4), and position this locus on the molecular linkage map of lettuce, which shows that these techniques have sufficient resolution to be used in a genetic context in lettuce.

Overexpression of AmRosea1 Gene Confers Drought and Salt Tolerance in Rice.

Ectopic expression of the MYB transcription factor of AmROSEA1 from Antirrhinum majus has been reported to change anthocyanin and other metabolites in several species. In this study, we found that overexpression of AmRosea1 significantly improved the tolerance of transgenic rice to drought and salinity stresses. Transcriptome analysis revealed that a considerable number of stress-related genes were affected by exogenous AmRosea1 during both drought and salinity stress treatments. These affected genes are involved in stress signal transduction, the hormone signal pathway, ion homeostasis and the enzymes that remove peroxides. This work suggests that the AmRosea1 gene is a potential candidate for genetic engineering of crops.

Comparative performance of spectral and thermographic properties of plants and physiological traits for phenotyping salinity tolerance of wheat cultivars under simulated field conditions.

Successful plant breeding in saline environments requires high-throughput phenotyping techniques to differentiate genotypes for salinity tolerance. This study employed advanced, non-destructive sensing technologies to identify traits contributing to salinity tolerance in wheat (Triticum aestivum L.). Plants were grown in large containers to simulate field conditions for control, salinity stress alone, and combined salinity and drought stress treatments. The comparative performance of spectral reflectance sensing, thermography, digital imaging, and the assessment of physiological traits of two wheat cultivars were tested at booting, anthesis and grain filling. Variation in grain yield between the two cultivars was significant for all treatments (controls, P<0.01; others, P<0.001), whereas there were no significant differences in straw DW regardless of treatment. Among the spectral and thermographic assessments, spectral indices were sufficiently sensitive to detect genotypic differences in salinity tolerance among the wheat cultivars after anthesis for the salinity alone and combined treatments. In contrast, physiological traits such as leaf water status and photosynthetic properties demonstrated no differences between the wheat cultivars for either the salinity alone or the combined treatments. These results suggest that spectral sensing has the potential for high-throughput screening of phenotypic traits associated with salinity tolerance of wheat cultivars.

Recovery from hybrid breakdown in a marine invertebrate is faster, stronger and more repeatable under environmental stress

Understanding how environmental stress alters the consequences of hybridization is important, because the rate of hybridization and the likelihood of hybrid speciation both appear elevated in harsh, disturbed or marginal habitats. We assessed fitness, morphometrics and molecular genetic composition over 14 generations of hybridization between two highly divergent populations of the marine copepod Tigriopus californicus. Replicated, experimental hybrid populations in both control and high-salinity conditions showed a decline in fitness, followed by a recovery. Recovery was faster in the salinity stress treatment, returning to parental levels up to two generations earlier than in the control. This recovery was stable in the high-salinity treatment, whereas in the control treatment, fitness dropped back below parental levels at the final time point. Recovery in the high-salinity treatment was also stronger in terms of competitive fitness and heat-shock tolerance. Finally, consequences of hybridization were more repeatable under salinity stress, where among-replicate variance for survivorship and molecular genetic composition was lower than in the control treatment. In a system with low effective population sizes (estimates ranged from 17 to 63), where genetic drift might be expected to be the predominate force, strong selection under harsh environmental conditions apparently promoted faster, stronger and more repeatable recovery from depressed hybrid fitness.

Cloning and characterization of the pepper CaPAO gene for defense responses to salt-induced leaf senescence.

BackgroundPheophorbide a oxygenase (PAO) is an important enzyme in the chlorophyll catabolism pathway and is involved in leaf senescence. It opens the porphyrin macrocycle of pheophorbide a and finally forms the primary fluorescent chlorophyll catabolite. Previous studies have demonstrated the function of PAO during cell death. However, the characterizaton of PAO during leaf senescence induced by environmental factors is not well understood.MethodsHomology-based cloning and RACE techniques were used to obtain the full-length cDNA of the CaPAO gene. CaPAO expression was determined by quantitative real-time PCR. Function of CaPAO gene were studied using virus-induced gene silencing and transgenic techniques with tobacco plants (Nicotiana tabacum).ResultsA novel PAO gene CaPAO was isolated from pepper (Capsicum annuum L.). The full-length CaPAO cDNA is comprised of 1838 bp, containing an open reading frame of 1614 bp, and encodes a 537 amino acid protein. This deduced protein belongs to the Rieske-type iron-sulfur superfamily, containing a conserved Rieske cluster. CaPAO expression, as determined by quantitative real-time PCR, was higher in leaves than roots, stems and flowers. It was upregulated by abscisic acid, methyl jasmonate and salicylic acid. Moreover, CaPAO was significantly induced by high salinity and osmotic stress treatments and also was regulated by Phytophthora capsici. The virus-induced gene silencing technique was used to silence the CaPAO gene in pepper plants. After 3 days of high salt treatment, the chlorophyll breakdown of CaPAO-silenced pepper plants was retarded. RD29A promoter-inducible expression vector was constructed and transferred into tobacco plant. After 7 days of salt treatment, the leaves of transgenic plants were severely turned into yellow, the lower leaves showed necrotic symptom and chlorophyll content was significantly lower than that in the control plants.ConclusionsThe expression of CaPAO gene was induced in natural senescence and various stresses. The CaPAO gene may be related to defense responses to various stresses and play an important role in salt-induced leaf senescence.

Effect of Salinity Stress and Surfactant Treatment on Physiological Traits and Nutrient Absorption of Fenugreek Plant

Salinity is considered as a major abiotic stress affecting crop production in arid and semi-arid regions in the world. Surfactants can improve water-use efficiency in saline soils and improve crop yield. This study was conducted to evaluate the effect of salinity stress and surfactant treatments on photosynthetic pigments and nutrition elements of fenugreek in the Crop and Soil Science greenhouse at the Pennsylvania State University (University Park, PA, USA) in 2013. The experiment was conducted using a 5 × 3 factorial randomized complete block design with three replications. Factor A consisted of five salinity levels [0, 4, 6, 8, and 10 ds m–1 sodium chloride (NaCl)] while factor B consisted of three nonionic surfactant levels (0, 1, and 3 ppm). The results indicated a stepwise reduction in photosynthetic pigments of fenugreek as salt stress increased, however, Peroxidase and polyphenol oxidase activity increased in fenugreek leaves as salinity stress increased. Levels of surfactant application had different effects on nutrient uptake. Some nutrient elements such as sodium, phosphorus, copper, manganese, and zinc content increased while others decreased at high salinity conditions. Surfactant application rate of 3 ppm at moderate and high salinity levels and 1 ppm at lower salinity levels had a good performance in enhancing the total photosynthetic and carotenoid activities in fenugreek.

Nutrient addition amplifies salinity-dependent differences in competitive ability of invasive and native vines

Invasive plants may have greater competitive ability than native species and greater invasion success in fertile habitats. However, they may not have high tolerance of abiotic stress and enriched resources may not increase invasion success in stressful habitats such as coastal areas with high soil salinity. We conducted a greenhouse experiment using the invasive vine Ipomoea cairica, which is expanding into coastal areas in South China, and the widespread native vine Merremia hederacea. Pots received two invasive vines, two native vines, or one of each. They were assigned nutrient (water vs. Hoagland’s solution) and salinity stress (water vs. 4 g L−1 NaCl) treatments in a factorial design. Salinity decreased plant biomass and nutrient increased plant biomass, especially without salinity. Ipomoea cairica were larger or similar to natives in monoculture. Without salinity, M. hederacea was larger than I. cairica in mixed culture, especially with nutrients. In saline conditions, I. cairica had greater competitive ability, which was increased by nutrient. Ipomoea cairica had higher root:shoot and nitrogen concentration in non-saline conditions, while M. hederacea had higher root: shoot and SLA in saline conditions. Our results indicate that competitive abilities of the two species depend on salinity and that nutrient addition only magnified the differences between them. This suggests that nutrient addition may increase invasion success but only in habitats where conditions were already suitable for invasion. The mismatch between the competition results in monoculture and mixed culture suggests caution in inferring the effects of environmental factors on competition based on measures of individual performance.