Low Salinity Treatments Research Articles

Effects of the harmful algal bloom toxin, okadaic acid, on the mechanoreceptors of larval anchoveta (Engraulis ringens) under varying environmental conditions

The effect of the combination of marine toxins produced by algal blooms, in conjunction with varying environmental characteristics on organisms in the water column, is a poorly explored research field. Pelagic fish species of commercial importance, such as anchoveta (Engraulis ringens) in central Chile, may be exposed to these combined factors in a climate change scenario. This is observed from documented changes in the length of the upwelling season, frequency of upwelling events, and the increased frequency of atmospheric rivers affecting the southern spawning zone of this species. This study evaluated the integrity of hair cells in neuromasts, mechanosensory organs present in fish larvae, under exposure to different combinations of the algal bloom-produced okadaic acid OA (1 ng mL−1), and two temperature (12 and 14°C), and salinity treatments (historically more frequent: 34 PSU- 12°C; expected: 32 PSU - 14°C). Viable hair cells were counted in newly hatched larvae from the Biobío region, central Chile. Results showed a significant decrease in the average number of viable hair cells per neuromast (from 6.1 ± 1.6 to 4.0 ± 1.2) under lower salinity treatments (32 PSU) compared to normal conditions. Additionally, a seasonal trend was observed with fewer viable cells (from 7.4 ± 1.2 to 4.4 ± 1.1) as the fish species’ reproductive period progressed. The combined effect of OA exposure and modifications with the environmental factors also resulted in a significant decrease of up to 70% in the number of viable hair cells in larvae exposed to OA and high temperatures, indicating damage influenced by the toxin along with a synergistic and/or additive role of temperature. These findings reveal how the lipophilic toxin okadaic acid, produced by harmful algal blooms, interacts with abiotic environmental factors affecting coastal ecologically and socio-economically important organisms. This emphasizes the need to consider multiple factors when studying the effects of marine toxins.

Effect of low-salinity seawater transient on antioxidant capacity, muscle quality and intestinal microorganism of crucian carp (Carassius auratus gibelio)

Freshwater fish are frequently disliked by consumers due to their fishy odor and loose texture. Therefore, salinity treatment before market release is crucial for improving the muscle quality of freshwater fish. In this study, Carassius auratus gibelio was temporarily reared in low-salinity seawater (6 ppt) for 15 days, and changes of antioxidant levels, muscle texture, and intestinal microbial were determined. After temporary rearing in seawater, the hardness, gumminess, and chewiness of the muscle texture improved, and the relative contents of fishy and fatty odors decreased. This indicated that low-salinity treatment can enhance muscle quality and flavor while reducing fishy odor. According to microbiome research, low-salinity saltwater temporarily reduced the relative abundance of some opportunistic pathogens, such as Vibrio (from 47.61% to 0.1%) and Shewanella (from 15.20% to 5.86%) in the intestinal tract of crucian carp, and increased the relative abundance of beneficial bacteria, such as Sphingomonas (from 2.52% to 28.38%). This study can provide a reference for using low-salinity seawater for temporary rearing to enhance the quality of fish prior to marketing.

Low salinity influences the dose-dependent transcriptomic responses of oysters to cadmium

Species in estuaries tend to undergo both cadmium (Cd) and low salinity stress. However, how low salinity affects the Cd toxicity has not been fully understood. Investigating the impacts of low salinity on the dose-response relationships between Cd and biological endpoints has potential to enhance our understanding of the combined effects of low salinity and Cd. In this work, changes in the transcriptomes of Pacific oysters were analyzed following exposure to Cd (5, 20, 80 μg/L Cd2+) under normal (31.4 psu) and low (15.7 psu) salinity conditions, and then the dose-response relationship between Cd and transcriptome was characterized in a high-throughput manner. The benchmark dose (BMD) of gene expression, as a point of departure (POD), was also calculated based on the fitted dose-response model. We found that low salinity treatment significantly influenced the dose-response relationships between Cd and transcripts in oysters indicated by altered dose-response curves. In details, a total of 219 DEGs were commonly fitted to best models under both normal and low salinity conditions. Nearly three quarters of dose-response curves varied with salinity condition. Some monotonic dose-response curves in normal salinity condition even were replaced by nonmonotonic curves in low salinity condition. Low salinity treatment decreased the PODs of differentially expressed genes induced by Cd, suggesting that gene differential expression was more prone to being triggered by Cd in low salinity condition. The changed sensitivity to Cd in low salinity condition should be taken into consideration when using oyster as an indicator to assess the ecological risk of Cd pollution in estuaries.

Fast screening method to identify salinity tolerant strains of foliose Ulva species. Low salinity leads to increased organic matter of the biomass

Sea lettuce (Ulva) is recognised for its potential in food, pharmaceutical, nutraceutical, biorefinery and bioremediation industries and is increasingly being cultivated. The requirements of those industries vary widely in terms of biomass composition. Ulva biomass composition and growth is known to be directly influenced by environmental factors, e.g., temperature, light, salinity, nutrient availability as well as by genetic factors and likely by microbiome composition. In order to select for the highest yielding strains in a given environment, we tested the suitability of common-garden experiments, i.e., the co-cultivation of different strains grown under shared conditions. Fifteen strains from six different foliose Ulva species were grown together under two different salinities, 35 ppt and 15 ppt. After 32 days, only U. australis strains remained at both salinities. If selection at low salinity was mostly based on survival, the selection process at seawater salinity was driven by competition, largely based on growth performance. Growth rates after a month were very similar at both salinities, suggesting the U. australis strains cope equally well in either condition. However, the composition of the biomass produced in both environments varied, with the content of all organic compounds being higher at low salinity, and the ash content being reduced in average by 66%. To summarize, this study provides an established bulk-selection protocol for efficiently screening large numbers of locally-sourced strains and highlights the potential of low salinity treatments for increased organic matter content, particularly in carbohydrates.

Artemia biomass: A functional live maturation feed for Indian white shrimp, Penaeus indicus broodstock, and its culture prospective under diverse management regime

Artemia biomass production in a controlled biosecure system can be popularised in inland or coastal areas where accessibility to saltpan is limited. Against this background, four sets of experiments were executed to optimize different management regimes in Artemia biomass production, and to explore its role as a maturation diet for Indian white shrimp, Penaeus indicus. In experiment, I, Artemia biomass production was carried out in autotrophic (microalgae, TA), heterotrophic (TH), and mixotrophic (TMX) rearing systems for 18 days. Experiment II was conducted to evaluate Artemia biomass production under diverse salinity regimes (10, 15, 20, 30, 40, and 50 ppt), and in experiment III, the effect of varying stocking densities of Artemia (300, 600, 1200, and 1800 nos L−1) in production was attempted. In experiment IV, the role of adult Artemia (live, frozen, and hormone-enriched) as a maturation diet for P. indicus (36.40 ± 0.3 g) was explored, and the sex steroid profile of adult Artemia was compared with other fresh maturation feeds (polychaete, clam, and squid). At the end of Exp 1, significantly higher (P < 0.05) yields were recorded in mixotrophic (1.30 ± 0.95 kg m−3) and heterotrophic groups, (1.22 ± 0.15 kg m−3) compared with autotrophic units (0.36 ± 0.47 kg m−3). However, omega 3 fatty acids (13.92 ± 0.73%) were highest in the autotrophic system compared to TMX (11.97 ± 0.84%) and TH (8.71 ± 0.31%). In Exp II, the highest (p < 0.05) production (1.52 ± 0.13 kg m−3) was recorded at 50 ppt followed by 40 ppt (1.29 ± 0.08 kg m−3) and the lowest at 10 ppt (0.54 ± 0.01 kg m−3). The highest egg-bearing population (%) was recorded at 40 ppt (30.47 ± 3.09%) followed by 30 ppt (12.63 ± 0.82%) and 50 ppt (9.29 ± 0.80%) while none of the Artemia got matured at lower salinity treatments. The stocking density-dependent inverse relation (p < 0.01) in survival (17–67%) was registered among the treatments in Exp III with no variation (p < 0.05) in total productivity (1.26 to 1.10 kg m−3). At the end of Exp IV, 100 ± 0, 87.5 ± 7.2, and 46.6 ± 3.3% of the broodstock fed with enriched, live, and frozen Artemia had matured ovaries, respectively. A comparative analysis of sex steroids in Artemia and other fresh broodstock feeds revealed the highest (p < 0.01) 17-β-estradiol level in polychaete (998 ± 33 pg 100 mg) followed by Artemia (519 ± 28 pg 100 mg−1), clam (195 ± 29 pg 100 mg −1) and squid (61 ± 10.69 pg 100 mg−1). The study indicated mixotrophic system with 300 no L−1 density at 40 ppt can yield the optimal highest production with a better nutritional profile and higher matured population. This strongly suggests the flexibility of mixotrophic-based culture units compared with a single food source system. The presence of sex steroids in adult Artemia provides its scope as a quality fresh maturation diet and can open new vistas for its wide acceptability as SPF live maturation diet for commercial shrimp hatcheries.

Mechanisms for improving the quality of crucian carp (Carassius auratus) by short-term low-salinity treatment revealed by UPLC-MS and GC–MS

Mechanisms for improving the quality of crucian carp (Carassius auratus) by short-term low-salinity treatment revealed by UPLC-MS and GC–MS

Short term decreases in salinity, combined with the right choice of species, can allow for a more nutritious sea lettuce lipid profile

The sea lettuce Ulva spp is becoming an increasingly important macroalgae for aquaculture. Sea lettuce can be grown on- and off-shore, displays high growth rates, and its biomass possesses attractive nutritional benefits. Among those are their fatty acids (FA) and lipid profiles, rich in omega 3 Polyunsaturated Fatty Acids (PUFAs) as well as bioactive lipids. In order to tailor those properties for food applications, we explored the use of a short-term (seven days) low salinity treatment to modulate the lipid profile of two species of Ulva. We found large quantitative differences between species, and while a low-salinity treatment negatively affected growth, Ulva australis’ lipid profile was positively impacted. Total FA particularly ɷ-3 PUFAs, increased three-fold, as well as most polar lipid species including known bioactive compounds. This study highlights profound differences between species and describes a simple method to increase the nutritional properties of Ulva biomass for food applications.

Salinity and cultivar effects on alfalfa forage yield and nutritive value in a Mediterranean climate

AbstractBackgroundSoil and water salinity are increasing problems worldwide, causing significantly reduced crop yields. Alfalfa (Medicago sativa L.) is often listed as salt‐sensitive, but field testing of improved cultivars is limited. Forage systems and improved high‐quality alfalfa varieties are needed to enable crop production under high salinity (HS) conditions.MethodsThe objective of this study was to measure the yield and quality response of alfalfa to high saline conditions in the field and to document the relative saline tolerance of its varieties. HS irrigation water (electrical conductivity of water, or ECw 8.0–11.0 dS m−1) was applied to 33 nondormant alfalfa cultivars and were compared with low salinity (LS) treatments (ECw 0.5–1.2 dS m−1) over 4 years in a Mediterranean environment on a clay loam soil utilizing a split‐plot design. Crops were harvested seven to eight times per year, and the forage quality was measured on selected harvests utilizing near‐infrared spectroscopy.ResultsThe average yield loss due to HS treatment was 23.9% compared with LS treatment, but yields averaged 23.4 Mg ha−1 under HS over the 3 full years of production. This level of production is considered to be economically viable in this region. Differences in salinity tolerance between lines were identified in the field; individual cultivars lost 5%–35% of their LS yield when grown under HS conditions. Forage quality was significantly improved under HS versus LS conditions, but improvements were negatively correlated with biomass yield (R2 &gt; 0.81), similar to responses observed in drought‐stressed alfalfa.ConclusionsThese yield results confirm greenhouse studies, indicating that alfalfa is highly salt tolerant once established in the field, with potential for further improvement with tolerant cultivars. Salinity tolerance should be chosen based on total biomass yield as well as on the salinity tolerance index (HS yield relative to LS yield). Agronomic practices to mitigate salinity and sodicity are critical, along with improved cultivars.

Function of Soybean miR159 Family Members in Plant Responses to Low Phosphorus, High Salinity, and Abscisic Acid Treatment

MicroRNAs (miRNAs) regulate plant growth and development and plant responses to biotic and abiotic stresses. Although extensive studies show that miR159 family members regulate leaf and flower development in Arabidopsis thaliana, the roles of miRNAs in soybean (Glycine max) are poorly understood. Here, we identified six MIR159 genes in soybean, MIR159a–MIR159f, and investigate their expression patterns in plants under low-phosphorus (low-P), NaCl, or abscisic acid (ABA) treatments. In soybean leaves, MIR159e and MIR159f expression was induced by low-P treatment, while in roots, MIR159b, MIR159c, MIR159e, and MIR159f expression was upregulated. In flowers, low-P led to upregulation of MIR159a, MIR159b, MIR159c, and MIR159f but downregulation of MIR159d and MIR159e. In soybean nodules, MIR159b was upregulated but MIR159a, MIR159c, and MIR159d was downregulated under P deficiency. NaCl treatment induced MIR159a, MIR159b, MIR159c, and MIR159e expression in leaves and MIR159a–MIR159f expression in roots. ABA treatment upregulated MIR159a, MIR159b, and MIR159c but downregulated MIR159d, MIR159e, and MIR159f in leaves. These results suggest that miR159 family members function in plant abiotic stress responses. Moreover, total P content in leaves was significantly lower in plants overexpressing MIR159e than in the wild type, suggesting that miR159e may regulate P absorption and transport in soybean plants.

Physiological-dependent alterations on transcriptomic and proteomic patterns of the single and combined temperature and salinity-exposed hybrid grouper, Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂

Global warming and the changes in environmental conditions such as temperature and salinity may affect the health of marine species. However, the underlying mechanisms remain poorly characterized. The objectives of the present study were to examine the liver transcriptome and proteome of the marine species, hybrid grouper (E. fuscoguttatus ♀ × E. lanceolatus ♂), to assess which physiological pathways are modulated by exposure to climate change-related stressors, how the responses vary with exposure duration, and whether they represent adaptive or maladaptive changes. To answer these questions, the hybrid grouper was subjected to single stressors (elevated temperatures, reduced salinity) or stressor combinations for 3 or 14 days. As endpoints, we examined changes in body and organ growth, liver histopathology, lipid accumulation, and alterations of the liver transcriptome and proteome. The results demonstrated that the elevated temperature resulted in reduced body weight and a reduced liver-somatic index after a 14-day exposure. The spleen-somatic index was significantly decreased compared to controls after 3-day treatment. At the transcriptomic level, the pathways with the greatest numbers of differentially expressed genes at day 3 of exposure were immune-related in all treatment groups. After 14 days of exposure, the transcriptomic and proteomic analyses showed that metabolic and protective processes became activated. The increased lipid droplet accumulation in the hepatocytes is corroborated by the transcriptomic/proteomic findings which show alterations in the pathways of lipid metabolism and fatty acid oxidation. While these changes may represent adaptive responses, the increase of hepatic lipid accumulation despite an overall loss of liver and body weight may represent a maladaptive process. Overall, the physiological responses of the hybrid grouper showed a clear time dependency, and they were partly stressor-specific, with the low salinity treatment separating from the treatments with elevated temperature. When both stressors were combined, the temperature effect dominated the salinity effect.

Moderate Salinity Stress Increases the Seedling Biomass in Oilseed Rape (Brassica napus L.).

Oilseed rape (Brassica napus L.), an important oil crop of the world, suffers various abiotic stresses including salinity stress during the growth stage. While most of the previous studies paid attention to the adverse effects of high salinity stress on plant growth and development, as well as their underlying physiological and molecular mechanisms, less attention was paid to the effects of moderate or low salinity stress. In this study, we first tested the effects of different concentrations of NaCl solution on the seedling growth performance of two oilseed rape varieties (CH336, a semi-winter type, and Bruttor, a spring type) in pot cultures. We found that moderate salt concentrations (25 and 50 mmol L-1 NaCl) can stimulate seedling growth by a significant increase (10~20%, compared to controls) in both above- and underground biomasses, as estimated at the early flowering stage. We then performed RNA-seq analyses of shoot apical meristems (SAMs) from six-leaf-aged seedlings under control (CK), low (LS, 25 mmol L-1), and high (HS, 180 mmol L-1) salinity treatments in the two varieties. The GO and KEGG enrichment analyses of differentially expressed genes (DEGs) demonstrated that such a stimulating effect on seedling growth by low salinity stress may be caused by a more efficient capacity for photosynthesis as compensation, accompanied by a reduced energy loss for the biosynthesis of secondary metabolites and redirecting of energy to biomass formation. Our study provides a new perspective on the cultivation of oilseed rape in saline regions and new insights into the molecular mechanisms of salt tolerance in Brassica crops. The candidate genes identified in this study can serve as targets for molecular breeding selection and genetic engineering toward enhancing salt tolerance in B. napus.

Physiological and life history responses in a mayfly (Callibaetis floridanus) inhabiting ponds with saltwater intrusion

Freshwater salinity varies in natural systems and plays a role in species distribution. Anthropogenic alterations to freshwater salinity regimes include sea level rise and subsequent intrusion of saline waters to inland habitats. While mayflies are generalized to be sensitive to increasing salinity, we still know remarkably little about the physiological processes (and their plasticity) that determine the performance of species in a changing world. Here, we explored life-history outcomes and physiological plasticity in a population of Callibaetis floridanus (Ephemeroptera: Baetidae) from a coastal pond that routinely experiences saltwater intrusion. We reared naiads from egg hatch to adulthood across a gradient of increasing salinities (113, 5,020, 9,921 μS/cm). Radiotracer flux studies (22Na, 35SO4, and 45Ca) were conducted in naiads reared at each salinity, revealing a positive association between ionic concentration and uptake rates. However, the influence of rearing history on ionic influx rates was apparent when naiads were transferred from their respective rearing water to the other experimental conditions. For example, we observed that naiads reared in the low salinity treatment (113 μS/cm) had 10.8-fold higher Na uptake rates than naiads reared at 9,921 μS/cm and transferred to 113 μS/cm. Additionally, naiads acclimated to the higher salinity water exhibited reduced uptake in ion-rich water relative to those reared in more dilute conditions (e.g., in 9,921 μS/cm water, 113 and 5,020 μS/cm acclimated naiads had 1.5- and 1.1-fold higher Na uptake rates than 9,921 μS/cm acclimated naiads, respectively). We found no significant changes in survival (80 ± 4.4%, mean ± s.e.m.) or naiad development time (24 ± 0.3 days, mean ± s.e.m.) across these treatments but did observe a 27% decrease in subimago female body weight in the most dilute condition. This reduction in female weight was associated with higher oxygen consumption rates in naiads relative to the other rearing conditions. Collectively, these data suggests that saline adapted C. floridanus may be more energetically challenged in dilute conditions, which differs from previous observations in other mayfly species.

Genome-wide methylome and transcriptome dynamics provide insights into epigenetic regulation of kidney functioning of large yellow croaker (Larimichthys crocea) during low-salinity adaption

Owing to extreme precipitation and surface runoff, low-salinity stress has become a severe environmental concern restricting inshore cultivation of large yellow croaker (Larimichthys crocea). Thus, illuminating adaptive mechanisms and cultivating new varieties with higher adaptability is essential for ensuring future cultivation success. DNA methylation can affect adaptability by regulating gene expression; however, little is known about the regulation mechanism of DNA methylation in marine fish facing low-salinity stress. Thus, we systematically explored the methylation landscape in the kidney and the potential regulation mechanism under low-salinity stress. Compared to the controls (25‰ salinity), expression of renal DNA transmethylase genes (dnmt1, dnmt3bb) and demethylase genes (tet1, tet2 and tet3) was notably up-regulated, and the global genome DNA methylation level in kidney was increased in the low-salinity treatment (5‰ salinity). Transcriptome analysis identified 316 differentially expressed genes, and 3827 differentially methylated promoters were identified through whole genome bisulfite sequencing. Integrative analyses produced 41 differentially methylated genes (DMGs), the expression of which was negatively correlated with promoter methylation. These DMGs were significantly enriched with respect to ion exchange, energy metabolism, cytoskeleton system, signal transduction, and other biological processes. The present study provides new insights for understanding renal epigenetic regulation mechanism and the selection of potential DNA methylation markers correlated with low-salinity adaption, which is crucial for future selection of new varieties of large yellow croaker with better low-salinity adaptability.

Mercury photoreduction and photooxidation kinetics in estuarine water: Effects of salinity and dissolved organic matter

Net photoreduction of divalent mercury (Hg(II)) and volatilization of photoreduction products (i.e., elemental mercury (Hg(0))/dissolved gaseous mercury (DGM)) is a mechanism by which mercury burdens in ecosystems are lessened. The effects of salinity on mercury photoreactions were investigated while controlling the concentration of DOM (>1 kDa) using natural surface water from the tidal Jijuktu'kwejk (Cornwallis River) and processed with a tangential ultrafiltration-dilution technique. Pseudo first-order rate constants in estuarine water salinity dilutions ranged between 0.22 h−1 and 0.73 h−1. The amount of mercury available for photoreduction (Hg(II)RED) ranged between 67.2 and 265.9 pg. Pseudo first-order rate constants decreased with increasing salinity treatments (0–13.5 g L−1), with minimal change in rate constants occurring in higher salinity treatments (e.g. 20.3 or 26.8 g L−1), while Hg(II)RED increased with salinity. In lower salinity treatments, DOM was more photoactive. Taken together, results suggest changes in the mercury photoreduction mechanism from DOM-bound electron transfer to photochemically produced secondary reduction products with increasing salinity. Experiments examining photooxidation showed decreases in Hg (0) with longer exposure time, suggesting transformation of Hg(II)RED into a non-reducible form. This research highlights the importance of salinity and DOM interactions in estuarine surface water and their effects on mercury photochemistry.

Water-Salt Thresholds of Cotton (Gossypium hirsutum L.) under Film Drip Irrigation in Arid Saline-Alkali Area

Crop models are valuable tools for exploring the responses of crops to changes in environmental factors, and have been widely used to analyze the response of crops to varying soil water content and salinity levels in extreme drought and high salinity conditions. To obtain suitable water-salt thresholds and the total irrigation amount for cotton in the arid oasis of southern Xinjiang, the AquaCrop model was calibrated and validated using measured data from 2020 and 2021 (total irrigation amount: 255–480 mm; initial soil salinity levels: 0.2–0.6%). With the same initial soil water content, when the initial soil salinity &lt; 7 dS/m, cotton yield did not significantly change under different levels of total irrigation amount, while when the initial soil salinity was 10 dS/m, there was a significant difference in cotton yield with a total irrigation amount &gt; 300 mm. The total irrigation amount of 375 mm is the threshold for cotton at the low-salinity treatment, while it increases to 450 mm at the high-salinity treatment. Based on cotton performance with the AquaCrop model, the threshold values of soil salinity were 7, 9.3, 8.2 and 9.3 dS/m (ECe) during the cotton stage of seedling, squaring, flower-boll and maturity, respectively. The total irrigation amount of 450 to 500 mm could achieve a win-win scenario for both cotton yield and water use efficiency under sandy loam soil. In summary, this study can serve as a reference for regulating water and salt in arid saline-alkali regions.

Intensity and duration of salinity required to form adaptive response in C4 halophyte Kochia prostrata (L.) Shrad.

Plant adaptation to salinity is a highly multifaceted process, harnessing various physiological mechanisms depending on the severity and duration of salt stress. This study focuses on the effects of 4- and 10-day treatments with low (100 mM NaCl) and moderate (200 mM NaCl) salinity on growth, CO2/H2O gas exchange, stomatal apparatus performance, the efficiency of photosystems I and II (PS I and II), content of key C4 photosynthesis enzymes, and the accumulation of Na+, K+, and proline in shoots of the widespread forage C4 halophyte Kochia prostrata. Our data show that 4 days of low salinity treatment resulted in a decrease in biomass, intensity of apparent photosynthesis, and cyclic electron transport around PS I. It was accompanied by an increase in transpiration and Rubisco and PEPC contents, while the Na+ and proline contents were low in K. prostrata shoots. By the 10th day of salinity, Na+ and proline have accumulated; PS I function has stabilized, while PS II efficiency has decreased due to the enhanced non-photochemical quenching of chlorophyll fluorescence (NPQ). Thus, under low salinity conditions, Na+ accumulated slowly and the imbalance between light and dark reactions of photosynthesis was observed. These processes might be induced by an early sodium signaling wave that affects cellular pH and ion homeostasis, ultimately disturbing photosynthetic electron transport. Another adaptive reaction more “typical” of salt-tolerant species was observed at 200 mM NaCl treatment. It proceeds in two stages. First, during the first 4 days, dry biomass and apparent photosynthesis decrease, whereas stomata sensitivity and dissipation energy during dark respiration increase. In parallel, an active Na+ accumulation and a decreased K+/Na+ ratio take place. Second, by the 10th day, a fully-fledged adaptive response was formed, when growth and apparent photosynthesis stabilized and stomata closed. Decreased dissipation energy, increased WUE, stabilization of Rubisco and PEPC contents, and decreased proline content testify to the completion of the adaptation and stabilization of the physiological state of plants. The obtained results allowed us to conclude that the formation of a full-fledged salt-tolerant response common for halophytes in K. prostrata occurs by the 10th day of moderate salinity.

Effect of ionic adjustment frequency in low-salinity water on zootechnical performance, water quality and mineral composition of Litopenaeus vannamei in a synbiotic nursery system

Ions are important for shrimp metabolic processes and can affect their growth. However, little is known about the need to supplement the major ions to maintain an adequate Ca:Mg:K ratio for shrimp as well as how often these ratios should be adjusted during a culture cycle using low-salinity water so that shrimp growth is not affected. The aim of this study was to evaluate the effect of ionic adjustment frequencies in low-salinity water in a synbiotic nursery system and verify its effects on Litopenaeus vannamei growth, water quality, and mineral composition of microbial flocs and shrimp. The experiment was carried out for 40 days, with a density of 2000 post-larvae m−3. The following treatments were tested, in triplicate: SW (seawater - salinity 31 g L−1); SWD (seawater diluted to a salinity of 2.3 g L−1); 1IA (ionic adjustment to achieve Ca:Mg:K ratio of 1:3:1 only on day 1 - salinity 2.3 g L−1); 2IA (ionic adjustment to achieve Ca:Mg:K ratio of 1:3:1 on day 1 and day 20 - salinity 2.3 g L−1); and 3IA (ionic adjustment to achieve Ca:Mg:K ratio of 1:3:1 on day 1, day 10, and day 20 - salinity 2.3 g L−1). Shrimp were fed four times a day with a 45% protein diet. The synbiotic fertilization protocol used a powder blend of Bacillus subtilis, B. licheniformis, Pseudomonas sp., and instant dry biological yeast (Saccharomyces cerevisiae) every 3 days. Nitrogen compounds remained within the recommended levels (TAN = 0.66 mg L−1, NO2−-N = 0.52 mg L−1, NO3−-N = 1.91 mg L−1) for L. vannamei reared in low-salinity water. Mean weight (1.14 to 1.18 g), survival (88.61 to 94.44%) and yield (2.10 to 2.15 kg m−3) were not significantly different in low-salinity treatments but were higher than those found in SW treatment (mean weight = 1.02 g; survival = 84.72%; and yield = 1.73 kg m−3). Mineral concentration in microbial floc and shrimp biomass did not differ among the frequencies tested, only differing when compared to SW treatment. To evaluate the juvenile's resistance, an ammonia stress test was performed during 96 h, obtaining 100% survival for all treatments. According to the results, L. vannamei juveniles can be produced in diluted seawater (salinity 2.3 g L−1, Ca2+ = 38.0 mg L−1, Mg2+ = 96.0 mg L−1, K+ = 48.3 mg L−1, total alkalinity = 92.33 mg CaCO3 L−1, total hardness = 490.13 mg CaCO3 L−1, Ca:Mg:K ratio 1:2.5:1.3) without ionic adjustments and without water exchange for 40 days in the nursery phase using a synbiotic system without affecting production performance.

Responses of soil respiration to simulated groundwater table and salinity fluctuations in tidal freshwater, brackish and salt marshes

Hydrological and salinity fluctuations in coastal wetlands induced by climatic change (e.g., drought) and anthropogenic activities can significantly affect the blue carbon sink via soil respiration (CO2 emissions). However, little information is available on the interactive effects of the groundwater table and salinity on soil respiration in coastal wetlands. Here, in situ soil columns were collected from tidal freshwater wetlands, brackish wetlands, and salt marshes to conduct a simulated assessment of the effects of fluctuations in the groundwater table (−30 cm, −20 cm and −10 cm) and salinity (0 ppt, 12ppt, and 26 ppt) on soil respiration in the field. The results showed that soil respiration in tidal freshwater wetlands (0.56–2.1 μmol/m2/s) and salt marshes (0.19–2.02 μmol/m2/s) was higher than that in brackish wetlands (0.17–0.9 μmol/m2/s) in all groundwater table and salinity treatments. The diurnal variation in soil respiration in the three simulated wetlands showed a unimodal curve, while the peak time was influenced by the groundwater table and salinity, with the maximum occurring at 11 a.m.-2 p.m. Soil respiration in tidal freshwater wetlands and brackish wetlands was significantly higher in the deep (−30 cm) and medium (−20 cm) groundwater table treatments than in the shallow (−10 cm) groundwater table treatment (p < 0.05) and significantly higher in the low (0 ppt) and medium (12ppt) salinity treatments than in the high (26 ppt) salinity treatment (p < 0.05). However, soil respiration in salt marshes decreased significantly as the groundwater table and salinity increased (p < 0.05). The groundwater table and salinity exhibited significant interactive effects on soil respiration in brackish wetlands (p < 0.05) and salt marshes (p < 0.01). Additionally, significantly negative correlations were observed between soil respiration and groundwater table and salinity in three wetlands (p < 0.05). Soil respiration in the three wetlands was significantly and positively correlated with microbial biomass carbon (p < 0.05) and significantly and positively correlated with soil organic carbon and total nitrogen (p < 0.01). The findings of this work can help reduce the uncertainty of model to accurately estimate carbon cycling of coastal wetlands at local, regional and global scales, and improve the blue carbon sink of coastal wetlands by regulating the groundwater table and salinity levels in wetland restoration projects.

Response of yield and quality of greenhouse tomatoes to water and salt stresses and biochar addition in Northwest China

Improving productivity of saline soils under drought condition is critical for sustainable agricultural development in arid areas. Whether biochar addition can interact with drought and salinity on fruit yield and quality remains unclear. A pot study was conducted to examine the effects of water, salinity and biochar addition on tomato yield and quality in a solar greenhouse of northwest China. There were twelve treatments combining two irrigation levels of high (W1) and low irrigation (W2 = 2/3 W1), three salinity levels with 0%, 0.3% and 0.6% of soil dry weight salts, referred to S0, S1, and S2, respectively, and two biochar addition levels with 0 (B0) and 1% (B1) of soil dry weight. Biochar, water, salinity, and the interaction between water and salinity were found significant affecting yield and irrigation water productivity (IWP). Biochar addition reduced yield and IWP, ranging from by 7% of W2S0 to 43% of W1S2. The difference in yield and IWP between W1 and W2 was greater for lower salinity treatments. The reduction percentage of W2, relative to W1, was 70%, 38%, and 29% for yield, 58%, 14%, and 0.9% for IWP under S0, S1, and S2, respectively. The effects of water, salinity and biochar treatments was found inconsistent for different quality parameters. Adding biochar had no significant effect on firmness, and slightly increased total soluble solids (TSS) and Vitamin C (VC) at both irrigation levels, while lower irrigation and higher salinity generally led to higher TSS and VC. The absolute slope value of the linear regression of yield and quality parameters with soil electrical conductivity was smaller under W2, relative to W1, indicating that the salinity effect was less pronounced when water stress was greater. The results are valuable in developing and evaluating remedy measures for improving saline soil productivity in arid areas.

Increasing salinity stress decreases the thermal tolerance of amphibian tadpoles in coastal areas of Taiwan

Global warming is the main cause for the rise of both global temperatures and sea-level, both major variables threatening biodiversity. Rising temperatures threaten to breach the thermal limits of organisms while rising sea-level threatens the osmotic balance of coastal animals through habitat salinization. However, variations in thermal tolerance under different salinity stresses have not yet been thoroughly studied. In this study, we assessed the critical thermal maxima (CTmax) of amphibian tadpoles in different salinity conditions. We collected tadpoles of Duttaphrynus melanostictus, Fejervarya limnocharis and Microhyla fissipes from coastal areas and housed them in freshwater, low, and high salinity treatments for 7 days of acclimation. The CTmax, survival rate, and development rate of tadpoles in high salinity treatments were significantly lower than that of the two other treatments. Our results indicate that physiological performances and heat tolerances of tadpoles are negatively affected by salinization. Maximum entropy models showed that CTmax and sea-level rise are predicted to negatively affect the distribution of the three focal species. The present results suggest that global warming can lead to negative dual-impacts on coastal animals because of reduced thermal tolerances at elevated salinity. The impacts of global warming on anurans in coastal areas and other habitats impacted by salinization may be more severe than predicted and it is likely to cause similar dual-impacts on other ectotherms.