Salinity Exposure Research Articles

Effects of salinity stress on antioxidant status and inflammatory responses in females of a "Near Threatened" economically important fish species Notopterus chitala: a mechanistic approach.

In the present study, acute stress responses of adult female Notopterus chitala were scrutinized by antioxidant status and inflammation reaction in the gill and liver at five different salinity exposures (0, 3, 6, 9, 12 ppt). Oxidative defense was assessed by determining superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase, and glutathione reductase activities, while malondialdehyde (MDA), glutathione, and xanthine oxidase levels were determined as indicators of oxidative load. Pro-inflammatory cytokines (IL-1β, IL-6, IL-10, and TNFα) and caspase 1 levels were also analyzed. Expression levels of transcription factors (NRF2 and NF-κB) and molecular chaperons (HSF, HSP70, and HSP90) were estimated to evaluate their relative contribution to overcome salinity stress. MDA showed a significant (P < 0.05) increase (gill, + 25.35-90.14%; liver, + 23.88-80.59%) with salinity; SOD (+ 13.72-45.09%) and CAT (+ 12.73-33.96%) exhibited a sharp increase until 9 ppt, followed by a decrease at the highest salinity (12 ppt) (gill, - 3.92%; liver, - 2.18%). Levels of cytokines were observed to increase (+ 52.8-127.42%) in a parallel pattern with increased salinity. HSP70 and HSP90 expressions were higher in gill tissues than those in liver tissues. NRF2 played pivotal role in reducing salinity-induced oxidative load in both the liver and gills. Serum cortisol and carbonic anhydrase were measured and noted to be significantly (P < 0.05) upregulated in salinity stressed groups. Gill Na+-K+-ATPase activity decreased significantly (P < 0.05) in fish exposed to 6, 9, and 12 ppt compared to control. Present study suggests that a hyperosmotic environment induces acute oxidative stress and inflammation, which in turn causes cellular death and impairs tissue functions in freshwater fish species such as Notopterus chitala.

Transcriptome analysis reveals fluid shear stress (FSS) and atherosclerosis pathway as a candidate molecular mechanism of short-term low salinity stress tolerance in abalone

BackgroundTranscriptome sequencing is an effective tool to reveal the essential genes and pathways underlying countless biotic and abiotic stress adaptation mechanisms. Although severely challenged by diverse environmental conditions, the Pacific abalone Haliotis discus hannai remains a high-value aquaculture mollusk and a Chinese predominantly cultured abalone species. Salinity is one of such environmental factors whose fluctuation could significantly affect the abalone’s cellular and molecular immune responses and result in high mortality and reduced growth rate during prolonged exposure. Meanwhile, hybrids have shown superiority in tolerating diverse environmental stresses over their purebred counterparts and have gained admiration in the Chinese abalone aquaculture industry.The objective of this study was to investigate the molecular and cellular mechanisms of low salinity adaptation in abalone. Therefore, this study used transcriptome analysis of the gill tissues and flow cytometric analysis of hemolymph of H. discus hannai (DD) and interspecific hybrid H. discus hannai ♀ x H. fulgens ♂ (DF) during low salinity exposure. Also, the survival and growth rate of the species under various salinities were assessed.ResultsThe transcriptome data revealed that the differentially expressed genes (DEGs) were significantly enriched on the fluid shear stress and atherosclerosis (FSS) pathway. Meanwhile, the expression profiles of some essential genes involved in this pathway suggest that abalone significantly up-regulated calmodulin-4 (CaM-4) and heat-shock protein90 (HSP90), and significantly down-regulated tumor necrosis factor (TNF), bone morphogenetic protein-4 (BMP-4), and nuclear factor kappa B (NF-kB).Also, the hybrid DF showed significantly higher and sustained expression of CaM and HSP90, significantly higher phagocytosis, significantly lower hemocyte mortality, and significantly higher survival at low salinity, suggesting a more active molecular and hemocyte-mediated immune response and a more efficient capacity to tolerate low salinity than DD.ConclusionsOur study argues that the abalone CaM gene might be necessary to maintain ion equilibrium while HSP90 can offset the adverse changes caused by low salinity, thereby preventing damage to gill epithelial cells (ECs).The data reveal a potential molecular mechanism by which abalone responds to low salinity and confirms that hybridization could be a method for breeding more stress-resilient aquatic species.

Local Populations of Eastern Oyster from Louisiana Differ inLow‐SalinityTolerance

AbstractEastern oystersCrassostrea virginicasupport a critical commercial industry and provide many ecosystem services to coastal estuaries yet are currently threatened by changing estuarine conditions. A changing climate and the effects of river and coastal management are altering freshwater inflows into productive oyster areas, causing more frequent and extreme salinity exposure. Although eastern oysters are tolerant to a wide range of salinity means and variations, more frequent and extreme exposure to low salinity (&lt;5‰) impacts oyster populations and aquaculture operations. This study assessed four Louisiana eastern oyster stocks to explore population‐specific responses to low‐salinity exposure. Hatchery‐produced progeny (10–25 mm) were deployed in baskets kept off‐bottom on longline systems in a low‐salinity (mean ± 1 standard error of the mean daily salinity = 8.7 ± 0.2‰; range = 1.2–19.0‰) and a moderate‐salinity (16.8 ± 0.3‰; 4.8–30.0‰) environment for 1 year, beginning in December 2019, with growth and mortality determined monthly. Significant differences in cumulative mortality between stocks at the end of the study were found at the low‐salinity site, with the greatest increase in cumulative mortality occurring mid‐July to mid‐August. Mortality differences between stocks suggest that some eastern oyster populations (i.e., stocks) may be better suited to low salinity or low‐salinity events than others. This difference may be attributed to similarity between site of origin and grow‐out site conditions and/or to greater salinity variability and therefore higher phenotypic plasticity in some eastern oyster populations compared with others. The identification of oyster stocks able to survive under extreme low‐salinity conditions may facilitate the development of “low‐salinity‐tolerant” broodstock to support aquaculture in areas experiencing and predicted to experience low‐salinity events.

Tolerance Level of Domesticated Asian Red-Tail Catfish Hemibagrus Nemurus to Salinity, Acidity, and Temperature Variability

The Asian redtail catfish Hemibagrus nemurus is Indonesian native fish proposed for catfish culture diversification project. Prior to be commercialized and widely distributed, it is imperative to evaluate environmental tolerances of the catfish for successful breeding programs and its aquaculture development program. This research was carried out to evaluate the optimum tolerance range and physiological responses of domesticated H. nemurus exposed to different salinity, acidity, and temperature. Fish used in this experiment were the second generation of H. nemurus produced at the Research Institute for Freshwater Aquaculture and Fisheries Extension (RIFAFE), Bogor, West Java, Indonesia. A total of 12 fish for each treatment were exposed to different salinity (0 ppt (control), 5 ppt, 10 ppt, 12.5 ppt, 15 ppt and 17.5 ppt), pH (4, 5, 7 (control), 9 and 10), and temperatures (15℃, 20℃, 25℃, 28.5℃ (control), 32.5℃, 35℃, and 40℃) for 12 days observation until fish reached their Loss of Equilibrium (LOE). Cortisol, hemoglobin, and glucose were investigated to study the stress response happened. This research reveals that the domesticated Asian redtail catfish are able to be acclimated to slightly brackish-water environment (≤10 ppt), have more resilience in acidic than alkaline water (pH 5.0 to 7.35), and can adjust in wide range of temperatures (25℃ to 32.5℃). In salinity exposure, significant physiological effects existed between controls and treatments (P&lt;0.05) except glucose. For pH, cortisol was the best indicator to see the effect of exposure (P&lt;0.05). The last for temperature exposure, the only cortisol was enabled to be used as the indicator of stress response. From the study, it found that cortisol level analysis was the best indicator to detect stress responses of the catfish that would be important to mitigate unpredictable environmental events and early warnings in the changes of environmental quality in culture system. We would recommend that the domesticated H. nemurus can be developed for the new catfish aquaculture candidate as it met a requirement to tolerance evaluation on different water quality levels which its responses was commonly similar compared to other existing aquaculture species.

Chronic Road Salt Exposure Across Life Stages and The Interactive Effects of Warming and Salinity in a Semiaquatic Insect.

The salinization of freshwater habitats from winter road salt application is a growing concern. Understanding how taxa exposed to road salt run-off respond to this salinity exposure across life history transitions will be important for predicting the impacts of increasing salinity. We show that Leucorrhinia intacta Hagen, 1861 (Odonata: Libellulidae) dragonflies are robust to environmentally relevant levels of salt pollution across intrinsically stressful life history transitions (hatching, growth, and metamorphosis). Additionally, we observed no carry-over effects into adult dragonfly morphology. However, in a multiple-stressor setting, we see negative interactive effects of warming and salinity on activity, and we found that chronically warmed dragonfly larvae consumed fewer mosquitoes. Despite showing relatively high tolerance to salinity individually, we expect that decreased dragonfly performance in multiple-stressor environments could limit dragonflies' contribution to ecosystem services such as mosquito pest control in urban freshwater environments.

Developmental responses and survival of Anopheles stephensi larval stages at different salinity levels.

Anopheles stephensi is a newly invaded vector in Sri Lanka. It has been identified in coastal areas in the northern and eastern parts of the country and evidences the ability to breed in brackish water environments. Laboratory investigations were conducted with batches of 100 first and third instar larvae exposed to a salinity gradient (0-40ppt). Survival rates at 1h, 24h and until pupation were recorded for first and third instar larvae at different salinity levels. The experiment was repeated four times for both instars. Data were analysed using the general linear model and probit analysis. Significant variations in adult emergence were observed from both larval stages at different salinity levels (p<0.05). The highest pupation rates were observed at 2.5ppt salinity. The survival rate of first instar larvae after 24h of salinity exposure was >80% up to 12.5ppt, while 100% mortality was observed for from the ≥25ppt level of salinity. More than 90% of the third instar larvae pupated from salinity levels <15ppt. The lowest survival rate was reported as 15.8±2.47% at 25ppt. This indicates a high potential of increasing density of A. stephensi in coastal ecosystems in lagoons and other saline water bodies. Hence it is high time to redesign vector control interventions for vector breeding in coastal ecosystems.

Interactive effects of salinity and light on the growth and survivorship of mangrove Heritiera littoralis seedlings

ABSTRACT Salinity and light are two important environmental factors that interactively influence mangrove performance. Heritiera littoralis, a mangrove associate widely distributed in East Africa and southeast Asia, has been threatened by habitat loss throughout its range. Understanding the growth response of H. littoralis to salinity and light gradients is essential for its conservation, especially in the context of sea level increases. Here we investigated the interactive effects of salinity and light on the growth and survivorship of H. littoralis seedlings by conducting a greenhouse experiment with two-phase light × salinity treatments. The results showed that salinity and shading exerted negative effects on H. littoralis survivorship and growth in terms of seedling height increases, leaf number increases and total biomass. H. littoralis displayed higher sensitivity to salinity than to light, and the response to light depends on the salinity level. Furthermore, salinity exerted prolonged effects on the H. littoralis response to subsequent light and salinity conditions. Relative to seedlings with no previous salinity exposure, the seedlings with salinity exposure were less responsive to increases in subsequent light availability and allocated more biomass to below vs. aboveground parts, resulting in lower biomass. Together, these results indicate that H. littoralis growth is strongly influenced by salinity. To improve H. littoralis conservation, salinity effects interacting with light should be considered when restoring disturbed habitats for H. littoralis.

Quercus suber Roots Activate Antioxidant and Membrane Protective Processes in Response to High Salinity.

Cork oak (Quercus suber) is a species native to Mediterranean areas and its adaptation to the increasingly prevalent abiotic stresses, such as soil salinization, remain unknown. In sequence with recent studies on salt stress response in the leaf, it is fundamental to uncover the plasticity of roots directly exposed to high salinity to better understand how Q. suber copes with salt stress. In the present study we aimed to unveil the antioxidants and key-genes involved in the stress-responses (early vs. later responses) of Q. suber roots exposed to high salinity. Two-month-old Q. suber plants were watered with 300 mM NaCl solution and enzymatic and non-enzymatic antioxidants, lipid peroxidation and the relative expression of genes related to stress response were analysed 8 h and 6 days after salt treatment. After an 8 h of exposure, roots activated the expression of QsLTI30 and QsFAD7 genes involved in stress membrane protection, and QsRAV1 and QsCZF1 genes involved in tolerance and adaptation. As a result of the continued salinity stress (6 days), lipid peroxidation increased, which was associated with an upregulation of QsLTI30 gene. Moreover, other protective mechanisms were activated, such as the upregulation of genes related to antioxidant status, QsCSD1 and QsAPX2, and the increase of the antioxidant enzyme activities of superoxide dismutase, catalase, and ascorbate peroxidase, concomitantly with total antioxidant activity and phenols. These data suggest a response dependent on the time of salinity exposure, leading Q. suber roots to adopt protective complementary strategies to deal with salt stress.

Behavioral and histo-pathological indices of striped catfish (Pangasionodon hypophthalmus) exposed to different salinities

Salinity intrusion due to climate changes in the coastal area is substantially jeopardized for sustainable aquaculture. This study was focused on behavioral and histo-pathological changes (gills, liver and kidney) of striped catfish (Pangasionodon hypopththalmas) exposed to four salinities (0, 4, 8 and 12 ppt), each with three replications for 56 days. Both behavioral and histological analyses were carried out for durations of 7, 14, 28 and 56 days of exposure. Mild to moderate behavioral abnormalities such as rate of swimming, food intake, gill motion and convulsions were observed in 8 ppt, but pronounced alterations were detected at higher salinity (12 ppt), increasing with longer exposures. Similarly, mild to moderate histological anomalies in gills (hypertrophy of the chloride cell, telangiectasia at the tips of secondary lamellae, epithelial necrosis, fusion of some secondary lamellae and lifting of the lamellar epithelium), liver (vacuolation, blood congestion, melanomacrophage centers, patchy degeneration, necrosis and hypertrophy nucleus) and kidney (degeneration of renal tubule, enlarged Bowman's capsule, increased space in between glomerulus center, melanomacrophage centers, vacuolation and necrotic cell in the hematopoetic tissue) were detected in 8 ppt but pronounced alterations were detected at higher salinity (12 ppt) with increasing the days of exposure. This preliminary study revealed more profound responses to higher salinity exposure in the striped catfish, and this species could serve as a model bio-indicator in costal aquaculture.

Macroalgal substitution effect in diet on growth, body composition, and stress resistance of juvenile sea cucumber (Apostichopus japonicus) subjected to air and low salinity exposures

Macroalgal substitution effect in diet on growth, body composition, and stress resistance of juvenile sea cucumber (Apostichopus japonicus) subjected to air and low salinity exposures

Prolonged low salinity tolerance in Halodule wrightii Asch

The seagrass Halodule wrightii (shoal grass) is found throughout the Caribbean and Gulf of Mexico where it can be an important or dominant component of the flora. It is generally more tolerant to disturbance than other seagrass species, including tolerance to reduced salinity. This study investigated the low salinity tolerance of a population of H. wrightii that has a long history of exposure to river flooding located at Cat Island, Mississippi (MS). Plants were collected after record prolonged flooding of the Mississippi River in 2019 and subsequent reduced salinities at Cat Island, MS, then allowed to recover at a salinity of 25 before being subject to three low salinity exposures of 5, 10, and 15. Plants were still alive after more than 12 months even at the lowest salinity of 5. Morphological and biomass metrics were recorded at the end of this prolonged low-salinity exposure. Plants exhibited low biomass and shoot density. This population of H. wrightii was able to survive very low salinities for longer than previously reported. Other seagrass populations with enhanced tolerance to abiotic stressors may become important for survival as climate change alters coastal habitat conditions.

Chloride accumulation in aboveground biomass of three macrophytes (Phragmites australis, Juncus maritimus, and Typha latifolia) depending on their growth stages and salinity exposure: application for Cl- removal and phytodesalinization.

Anthropogenic activities can be the source of saline solid wastes that need to be treated to reduce their salt load to meet the purposes of reuse, valorization or storage. In this context, chloride remediation can be achieved using high-salt accumulating plants. However, there is very limited information on the comparative potential of different species in the same environment, and only scarce data concerning their efficiency as a function of growth stage. In order to rationalize these selection criteria, three macrophytes i.e., common reed (Phragmites australis), sea rush (Juncus maritimus), and cattail (Typha latifolia), were cultivated at two growth stages (6-months old and 1-year old) for 65 days in Cl− spiked substrates (from 0 up to 24 ‰ NaCl). The plants’ survival and potential capacity for removal of Cl− from substrates and accumulation in shoots were investigated. For the three studied species, mature and juvenile plants display a high tolerance to salinity. However, mature specimens with higher shoot biomass and Cl− contents are capable of greater chloride removal than juvenile plants. The sole exception is P. australis which displays just the same phytoremediation potential for both mature and juvenile specimens. Moreover, P. australis has the lowest potential when compared with other species, being 1.5 and 3 times lower than for J. maritimus and T. latifolia. When considering the plant growth and the shoot biomass production, chloride removal rates from the substrate point that mature J. maritimus should preferentially be used to design an operational chloride remediation system. The results highlight the relevance of considering the growth stage of plants used for Cl− removal.Highlights1) Mature and juvenile specimens of J. maritimus, P. australis, and T. latifolia have high salinity tolerance in solid media spiked up to 24 ‰ NaCl.2) Mature plants have generally better Cl− removal and phytoremediation performances than juvenile specimens.3) J. maritimus is the most effective species for chloride phytoremediation with high survival and high Cl− sequestration in shoots.4) T. latifolia has high Cl− removal in shoots and good remediation capacities but also shows sign of stress.5) P. australis shows low Cl− sequestration and is a poor candidate for chloride remediation from substrate.Supplementary InformationThe online version contains supplementary material available at 10.1007/s11356-021-17591-3.

Can anammox process be adopted for treating wastewater with high salinity exposure risk?

Anammox was a promising technology for nitrogen removal, and has been applied for treating many kinds of nitrogenous wastewaters. Considering the risk in high salinity of the municipal sewage in coastal city, the feasibility of Anammox process for treating low ammonia wastewater (around 50 mg L−1) with increasing salinity was investigated in this study. The results showed that the salinity in low concentrations (1–5 g L−1) had slight impact on the nitrogen removal and activity of Anammox bacteria but significantly improved its growth. The moderate salinity (10–40 g L−1) decreased the specific Anammox activity (SAA) to 8.11 from the initial 13.15 mg N g−1 SS h−1, but increased the abundance to 52.3% from 30.1% (Candidatus Kuenenia). High salinity (50–60 g L−1) performed severe inhibition on activity and abundance both, with the SAA decreased to 0 and abundance to 11.9%. The self-recovery performance was unsatisfactory when salinity was unavailable. A quadratic curve between the SAA and salinity concentration was fitted, and the IC50 was calculated as 42.1 g L−1 (NaCl). Anammox process could be directly adopted for treating low ammonia sewage with low salinity, whereas activity enhancement or adaption improvement should be pre-presented for treating sewage with moderate or high salinity.

Systematic analysis of the aroma profiles produced by Zygosaccharomyces rouxii Y-8 in different environmental conditions and its contribution to doubanjiang (broad bean paste) fermentation with different salinity

This study aimed to provide a systematic analysis of the effect of environmental factors on the growth and volatile flavor compounds (VFCs) production ability of Zygosaccharomyces rouxii Y-8 and further elucidate its contribution to doubanjiang fermentation in different salinity. Lower salinity (0–9%), acidic pH (4.5–5.5), moderate temperature (25–35 °C) and air exposure favored the growth and VFCs accumulation of Z. rouxii Y-8, which also had higher concentrations of key jiang flavor contributing compounds benzene ethanol, 2-methoxy-phenol and pyrazines. Interestingly, samples with higher VFCs concentration were found to contain less kinds of VFCs. When inoculated into doubanjiang fermentation, Z. rouxii Y-8 showed critical roles on the formation of VFCs in doubanjiang. Among doubanjiang samples fermented in different salinity, doubanjiang with 9% salinity had the highest kinds of VFCs. Moreover, its flavor was more balanced and the jiang flavor was stronger. This indicated that the presence of adequate salinity was necessary for Z. rouxii Y-8 to produce critical VCFs responsible for doubanjiang flavor. The results would provide researchers and manufacturers with a deeper understanding of the characteristics of Z. rouxii Y-8 and rationales to utilize Z. rouxii Y-8 as starter to produce high quality BBFFs.

Synergistic effects of salinity and temperature on the eastern oyster Crassostrea virginica throughout the lifespan

The eastern oyster Crassostrea virginica has a wide salinity tolerance, but all life stages are vulnerable to environmental extremes, and elevated temperatures can truncate the expected salinity tolerance. The rising water temperatures and more intense and variable storm events predicted to accompany global climate change therefore raise concerns for habitat suitability for ecologically important species such as the eastern oyster. To better understand environmental limitations, oysters of all life stages were exposed to a range of salinities (0-40) and temperatures (25 and 30°C) to test physiological tolerance to the combined effects of osmotic and thermal stresses. Elevated temperatures (30°C) amplified negative effects during exposure to salinity extremes at all life stages; however, tolerance to extremes increased with developmental stage (gametes &lt; embryos &lt; larvae &lt; spat &lt; adult). Gradual changes allow for a wider tolerance in juvenile oysters (spat) compared to acute changes, and short-term reprieves during low salinity exposure improved survival rates for adults. Overall, the present study found a threshold salinity of 15 for polyhaline oyster populations and highlights the importance of both rate of change and temperature as critical components of salinity tolerance. Additionally, salinities &lt;10 during the summer months could result in negative population effects, especially if extreme low salinity occurs during peak reproduction when pelagic gametes, embryos, and larvae are most vulnerable to environmental stresses. This work will benefit population models and inform resource management decisions regarding the timing of controlled freshwater releases.

Studi Morfometri dan Meristik Kantong Semar (Nepenthes spp.) yang Terpapar atau Tidak Terpapar Air Laut

Nepenthes or pitcher plant is one of the most exotic plants in the world. There are 82 species of Nepenthes in the world, and very few studies concerning salinity stress have been carried out. We have found one species of pitcher plant that was exposed to seawater, namely Nepenthes gracilis Korth. Sixty-eight individuals were exposed to seawater and the rest were not. Observing and measuring morphological characters and anatomical characters have been done to these two sample groups in order to reveal the adaptation expression to the salinity stress. Statistical analysis has also been carried out between both groups. Two samples showed that they have significant differences in the size of pitcher and leaf. The ones which were exposed to seawater had smaller pitchers and leaves than others. The exposed seawater pitcher plant also has thicker leaves and palisade than others. Additionally, salinity exposure tended to decrease the stomatal density. The possible reason for this pattern was discussed in this study.

Short-term behavioral responses and tolerance limits of red seabream Pagrus major fingerlings following sudden low salinity exposure

Short-term behavioral responses and tolerance limits of red seabream <i>Pagrus major</i> fingerlings following sudden low salinity exposure

MusaATAF2 like protein, a stress-related transcription factor, induces leaf senescence by regulating chlorophyll catabolism and H2 O2 accumulation.

NAC transcription factors are known for their diverse role in plants. In this study, we have demonstrated the role of MusaATAF2, a banana NAC transcription factor, in leaf senescence. Its expression gets strongly up-regulated during the early stress responses of drought and high salinity exposure and down-regulated under ABA application, which suggests MusaATAF2 is a stress-related NAC transcription factor. To study the role of MusaATAF2 in banana, we have transformed the banana embryogenic cells with MusaATAF2 coding region and generated transgenic banana plants. Overexpression of MusaATAF2 in banana plants caused yellow leaf phenotype under control condition, suggesting its role as a senescence-associated transcription factor. Transgenic banana leaves exhibited low chlorophyll content and high H2 O2 accumulation. Hormone analysis of the leaves demonstrated a higher accumulation of ABA in the transgenic plants than the controls. Transgenic plants overexpressing MusaATAF2 have a higher transcript abundance of two chlorophyll catabolic pathway genes (PAO and HCAR) and lower transcript abundance of ROS scavenging enzymes (TDP, THIO, CAT, APX, and PRXDN) than control. Together, all these analyses indicate that MusaATAF2 induces senescence by inducing chlorophyll degradation and H2 O2 accumulation in banana plants and controls its own expression using an ABA-dependent feedback loop.

Salinity thresholds for understory plants in coastal wetlands

The effects of sea level rise and coastal saltwater intrusion on wetland plants can extend well above the high-tide line due to drought, hurricanes, and groundwater intrusion. Research has examined how coastal salt marsh plant communities respond to increased flooding and salinity, but more inland coastal systems have received less attention. The aim of this study was to identify whether ground layer plants exhibit threshold responses to salinity exposure. We used two vegetation surveys throughout the Albemarle-Pamlico Peninsula (APP) of North Carolina, USA to assess vegetation in a low elevation landscape (≤ 3.8 m) experiencing high rates of sea level rise (3–4 mm/year). We examined the primary drivers of community composition change using Non-metric Multidimensional Scaling (NMDS) and used Threshold Indicator Taxa Analysis (TITAN) to detect thresholds of compositional change based on indicator taxa, in response to potential indicators of exposure to saltwater (Na, and the Σ Ca + Mg) and elevation. Salinity and elevation explained 64% of the variation in community composition, and we found two salinity thresholds for both soil Na+ (265 and 3843 g Na+/g) and Ca+ + Mg+ (42 and 126 µeq/g) where major changes in community composition occur on the APP. Similar sets of species showed sensitivity to these different metrics of salt exposure. Overall, our results showed that ground layer plants can be used as reliable indicators of salinity thresholds in coastal wetlands. These results can be used for monitoring salt exposure of ecosystems and for identifying areas at risk for undergoing future community shifts.

Genome-Wide Identification, Characterization, and Expression Analysis of DDE_Tnp_4 Family Genes in Eriocheir sinensis.

DDE transposase 4 (DDE_Tnp_4) family is a large endonuclease family involved in a wide variety of biological processes. However, little information is available about this family in crustaceans. In this study, we used HMMER to identify 39 DDE_Tnp_4 family genes in Eriocheir sinensis genome, and the genes were classified into four subfamilies according to phylogenetic analysis. Gene expansions occurred among E. sinensis genome, and synteny analysis revealed that some DDE_Tnp_4 family genes were caused by tandem duplication. In addition, the expression profiles of DDE_Tnp_4 family genes in E. sinensis indicated that subfamily I and II genes were up-regulated in response to acute high salinity and air exposure stress. E. sinensis is a kind of economical crustacean with strong tolerance to environmental stress. We confirmed the expansion of DDE_Tnp_4 family genes in E. sinensis and speculated that this expansion is associated with strong tolerance of E. sinensis. This study sheds light on characterizations and expression profiles of DDE_Tnp_4 family genes in E. sinensis and provides an integrated framework for further investigation on environmental adaptive functions of DDE_Tnp_4 family in crustaceans.