A review of the species,community, and ecosystem impacts of road salt salinisation in fresh waters

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Effects of environmental stress cascade up through four trophic levels in a salt marsh study system

1. Although in recent years there have been a number of studies demonstrating trophic cascades in terrestrial systems, it is still unclear what environmental conditions enable or enhance such cascades, especially among four trophic levels. 2. In this study, the influence of environmental stress (increased soil pore water salinity) on a four trophic level study system in a Florida salt marsh was examined by experimentally increasing soil pore water salinity. Effects of increased salinity on the quality of the host plant, Batis maritima, were assessed, as were resulting effects on the lepidopteran herbivore Ascia monuste, and the primary parasitoids and hyperparasitoids of its caterpillars. 3. Increased salinity altered host‐plant quality, which subsequently affected the consumer species. These effects of altered plant quality cascaded up through the herbivore and primary parasitoid to the hyperparasitoid Hypopteromalus inimicus, influencing its density, sex ratio, body size, and initial egg load. 4. These results demonstrate how heterogeneity in environmental stress can result in effects that cascade up through four trophic levels. We suggest that such strong effects at higher trophic levels may be more likely in systems in which relationships are more specific and intimate such as those among hosts, parasitoids, and hyperparasitoids.     

Context‐dependent effects of mycorrhizae on herbivore density and parasitism in a tritrophic coastal study system

1. Stressful abiotic conditions and mycorrhizal fungi have both been shown to influence plant quality significantly, yet the interactive effects of these factors on relationships among plants, herbivores, and natural enemies remain unclear. 2. In this study, the results of a factorial field experiment are reported in which the effects of plant stress and mycorrhizae on density and parasitism of three herbivores of Baccharis halimifolia L. were examined. 3. Plant stress was increased by adding salt to the soil, and association with mycorrhizal fungi was increased by inoculating plant roots. 4. Inoculation with mycorrhizal fungi resulted in increased density of all three herbivore species, but the effects of mycorrhizae on parasitism varied by species and with soil salinity levels. For the gall maker Neolasioptera lathami Gagne, mycorrhizae decreased parasitism regardless of soil salinity levels. For the leaf miners Amauromyza maculosa Malloch and Liriomyza trifolii Burgess, mycorrhizae effectively negated the decrease in parasitism resulting from increased salinity. 5. The results of this study show that the effects of mycorrhizae on parasitism may be context dependent, and can be positive or negative depending upon species and environmental conditions.     

Environmental Variables and Planktonic Communities in Two Ponds of El Hondo Wetland (SE Spain)

The annual cycle of physical and chemical variables and plankton dynamics was studied in two shallow ponds (East and West Ponds) of the El Hondo wetland, an ecosystem of international importance. Water conductivity increased up to 31–49 mS cm^–1 as water level decreased due to high evaporation and minimal water inputs. Initially considered mesohaline, the waters were reclassified as polyhaline during the hot season. EP was subject to successive desiccation‐flooding cycles, and flooding of the dried sediment caused the release of high concentrations of nitrogen and phosphorus compounds, which quickly depleted. The algal species composition was typical of eutrophic ecosystems, and the chlorophyll content indicated that EP was eutrophic and WP mesotrophic. Phytoplanktonic species richness and diversity were low in both ponds. Algal assemblages, in terms of biovolume, were mainly dominated by Dinophyceae in EP and by Cryptophyta in WP. The zooplankton community was dominated by Rotifers (Brachionus and Hexarthra), although Copepods and Ciliates were also important. Different water inputs to the ponds, partial drying in EP during the warm season with the subsequent higher increment of salinity, and the presence of dense populations of submerged macrophytes in WP, explain the differences in plankton communities found between the two ponds.     

Proteomics reveals the overlapping roles of hydrogen peroxide and nitric oxide in the acclimation of citrus plants to salinity

Hydrogen peroxide (H₂O₂) and nitric oxide (˙NO) are key reactive species in signal transduction pathways leading to activation of plant defense against biotic or abiotic stress. Here, we investigated the effect of pre‐treating citrus plants (Citrus aurantium L.) with either of these two molecules on plant acclimation to salinity and show that both pre‐treatments strongly reduced the detrimental phenotypical and physiological effects accompanying this stress. A proteomic analysis disclosed 85 leaf proteins that underwent significant quantitative variations in plants directly exposed to salt stress. A large part of these changes was not observed with salt‐stressed plants pre‐treated with either H₂O₂ or sodium nitroprusside (SNP; a ˙NO‐releasing chemical). We also identified several proteins undergoing changes either in their oxidation (carbonylation; 40 proteins) and/or S‐nitrosylation (49 proteins) status in response to salinity stress. Both H₂O₂ and SNP pre‐treatments before salinity stress alleviated salinity‐induced protein carbonylation and shifted the accumulation levels of leaf S‐nitrosylated proteins to those of unstressed control plants. Altogether, the results indicate an overlap between H₂O₂‐ and ˙NO‐signaling pathways in acclimation to salinity and suggest that the oxidation and S‐nitrosylation patterns of leaf proteins are specific molecular signatures of citrus plant vigour under stressful conditions.     

Interactive effects of mycorrhizal fungi,salt stress,and competition on the herbivores of Baccharis halimifolia

1. Plant stress and association with mycorrhizal fungi have been shown to significantly influence plant quality, yet their roles in influencing plant–insect interactions remain unclear. Even less is known about how these factors might interact with or be modified by within‐trophic level interactions. 2. In the present study, the results of a factorial field experiment are reported in which the effects of within‐trophic‐level interactions, plant stress, and mycorrhizae on three herbivores of Baccharis halimifolia were examined. 3. Plant stress was increased by adding salt to the soil, and availability of mycorrhizal fungi was increased by inoculating plant roots. These treatments were applied to plants with either low or high densities of a competitor (Trirhabda baccharidis). 4. For the two leaf miners, Amauromyza maculosa and Liriomyza trifolii, increased soil salinity and high densities of the competitor Trirhabdabaccharidis resulted in significant decreases in density. Neither of these treatments affected the gall maker Neolasioptera lathami. 5. Mycorrhizal fungi increased the densities of all three herbivores, possibly by increasing foliar nitrogen levels. For the two leaf miners, there was also evidence that mycorrhizae ameliorated the negative effects of salt stress. There was also evidence that high levels of competition dampened the positive effects of mycorrhizae on the two leaf miners.     

Seasonal changes in the germination responses of Hordeum maritimum and H. murinum seeds in relation to salinity,temperature and after‐ripening time

Abstract

The effects of temperature and salinity (NaCl) on germination of Hordeum maritimum With, (halophyte) and H. murinum L. (glycophyte) seeds were investigated. Dehulled caryopses were used for monthly germination trials, starting from November (120 days of after‐ripening in darkness at 20±1°C). Trials were continued for one year. Differences in germination response between the two species were observed, confirming that H. Maritimum is better adapted to high salinity levels and to variations in external temperature than H. murinum. H. maritimum showed a germination control mechanism related to after‐ripening time and based on seed dormancy break/resumption. At higher temperature (30°C), thermodormancy was also recorded. No germination strategies were observed in H. murinum that is relatively insensitive to the combined effects of temperature and salinity. Thus, in virtually all treatments, H. murinum exhibited a higher germination rate compared with H. maritimum, as early as 72 h after imbibition, suggesting that dormancy, both in the presence or absence of salt, is totally abolished by early fall or at the latest in winter.     

Diversity and salt tolerance of native Acacia rhizobia isolated from saline and non‐saline soils

Re‐establishing native vegetation in stressed soils is of considerable importance in many parts of the world, leading to significant interest in using plant–soil symbiont interactions to increase the cost‐effectiveness of large‐scale restoration. However, effective use of soil microbes in revegetation requires knowledge of how microbe communities vary along environmental stress gradients, as well as how such variation relates to symbiont effectiveness. In Australia, shrubby legumes dominate many ecosystems where dryland salinity is a major issue, and improving plant establishment in saline soils is a priority of regional management agencies. In this study, strains of rhizobial bacteria were isolated from a range of Acacia spp. growing in saline and non‐saline soils. Replicates of each strain were grown under several salinity levels in liquid culture and characterized for growth and salt tolerance. Genetic characterization of rhizobia showed considerable variation among strains, with salt tolerance and growth generally higher in rhizobial populations derived from more saline soils. These strains showed markedly different genetic profiles and generic affiliations to those from more temperate soils, suggesting community differentiation in relation to salt stress. The identification of novel genomic species from saline soils suggests that the diversity of rhizobia associated with Australian Acacia spp. is significantly greater than previously described. Overall, the ability of some symbiotically effective strains to tolerate high salinity is promising with regard to improving host plant re‐establishment in these soils.     

Growth of corn in saline waters

Eight cultivars of Zea mays plus the wild species Zea diploperennis were screened for seedling saline tolerance up to 3.2% NaCl. The best performances were given by the cultivars Mo 17 and commercial Hawaiian Super Sweet Hybrid. These two were then field grown on coral-cinder beds using drip irrigation with fresh of half-strength sea water (1.5–1.7% dissolved solids). Growth and chemical data for Mo 17 at 12 weeks show reduced growth but the same percentage dry matter. Ash, protein and total sulfur were higher in saline plants, silica and total phosphorus lower. Na, K. Mg, and Cl were elevated and Ca reduced slightly. Fe was also increased in saline plants. Both Mo 17 and Super Sweet Hybrid corn flowered and produced seed which retained essentially normal viability both in fresh and salt water.     

Ontogenetic changes in location and morphology of chloride cells during early life stages of the Nile tilapia Oreochromis niloticus adapted to fresh and brackish water

Ontogenetic changes in the location, size, density and morphology of chloride cells in the Nile tilapia Oreochromis niloticus adapted to fresh and brackish water are described using Na(+) /K(+) -ATPase immunohistochemistry, light microscopy (LM), scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM). The pattern of chloride cell distribution changed during development under both treatments, with chloride cell density decreasing significantly from hatch to 7 days post-hatch, but appearing on the inner opercular area at 3 days post-hatch and increasing significantly thereafter (P < 0·05). Chloride cells were always denser in fresh- than in brackish-water larvae. In both treatments, chloride cells located on the outer operculum and tail showed a marked increase in size with age, but cells located on the abdominal epithelium of the yolk sac and the inner operculum showed a significant decrease in size (P < 0·05). Chloride cells from brackish-water adapted larvae from 1 day post-hatch onwards were always significantly larger (P < 0·05) than those from freshwater-adapted larvae. SEM revealed structural differences in chloride cell apical morphology according to environmental conditions. There appears to be clearly defined temporal staging of the appearance of adaptive mechanisms that confer an ability to cope with varying environmental conditions during early development.     

Trade‐offs in osmoregulation and parallel shifts in molecular function follow ecological transitions to freshwater in the Alewife

Adaptation to freshwater may be expected to reduce performance in seawater because these environments represent opposing selective regimes. We tested for such a trade‐off in populations of the Alewife (Alosa pseudoharengus). Alewives are ancestrally anadromous, and multiple populations have been independently restricted to freshwater (landlocked). We conducted salinity challenge experiments, whereby juvenile Alewives from one anadromous and multiple landlocked populations were exposed to freshwater and seawater on acute and acclimation timescales. In response to acute salinity challenge trials, independently derived landlocked populations varied in the degree to which seawater tolerance has been lost. In laboratory‐acclimation experiments, landlocked Alewives exhibited improved freshwater tolerance, which was correlated with reductions in seawater tolerance and hypo‐osmotic balance, suggesting that trade‐offs in osmoregulation may be associated with local adaptation to freshwater. We detected differentiation between life‐history forms in the expression of an ion‐uptake gene (NHE3), and in gill Na⁺/K⁺‐ATPase activity. Trade‐offs in osmoregulation, therefore, may be mediated by differentiation in ion‐uptake and salt‐secreting pathways.     

Belemnite ecology and the environment of the Nusplingen Plattenkalk (Late Jurassic,southern Germany): evidence from stable isotope data

The late Kimmeridgian Nusplingen Plattenkalk (palaeolatitude ~30°N) is one of the well‐known European Plattenkalk konservatlagerstätten. The laminated limestones of this lagerstätte have been deposited in a shallow lagoon, surrounded by sponge‐microbial mounds, some of which formed small islands. Plattenkalk sediments are often thought to have been deposited below a halocline, which was induced by high evaporation rates. By measuring the stable isotope composition of belemnite rostra (n = 27) of the species Hibolithes semisulcatus, the depositional environment of the Nusplingen Plattenkalk has been investigated. Cathodoluminescence‐microscopy and trace element analysis have been applied to check for diagenetic alteration of the studied rostra. The mean δ¹³C of the well‐preserved rostra is +0.03 ± 0.27‰, the mean δ¹⁸O ?0.68 ± 0.3‰. A narrow range of stable isotope data acquired from an accumulation of rostra, regurgitated by a fish or reptile, supports the notion that belemnite calcite reflects environmental conditions. The palaeontological and sedimentological findings suggest that H. semisulcatus was autochthonous to the Nusplingen Plattenkalk. Anoxic conditions prevailed in the sediments and temporarily in the water‐column above the sediment/bottom water interface. A nektobenthic life style can be excluded for the Nusplingen belemnites; a demersal life style seems unlikely. Comparison with δ¹⁸O_bel data from other latitudes indicates that a latitudinal gradient played a role in the δ¹⁸O composition of seawater. A pelagic, inner shelf setting is therefore suggested for the Plattenkalk, an interpretation that is supported by palaeontological evidence. It is here proposed that the formation of the Nusplingen Plattenkalk was not caused by salinity stratification. It is further suggested that the belemnites were not restricted to deep‐water settings, but also occurred in shallow waters and higher in the water‐column.     

Salinity‐Gradient Power Generation with Ionized Wood Membranes

Reverse electrodialysis (RED) is known as an efficient way of converting the salinity gradient between river water and sea water into energy. However, the high cost and complex fabrication of the necessary ion exchange membranes greatly prohibit the development of the RED process. For the first time, an ionized wood membrane is demonstrated for this application, benefiting from the advantages of natural wood, which is abundant, low cost, sustainable, and easy to scale. The wood membrane maintains the aligned nanochannels of the cellulose nanofibers derived from the natural wood. The surface of the nanochannels can be functionalized to positively or negatively charged by in situ modifying the hydroxyl groups on the cellulose chains to quaternary ammonium or carboxyl groups, respectively. These charged aligned nanochannels serve as nanofluidic passages for selective ion transport with opposite polarity through the wood membrane, resulting in efficient charge separation and generating an electrochemical potential difference. The all‐wood RED device with 100 cells using a scalable stacking geometry generates an output voltage as high as 9.8 V at open circuit from a system of synthetic river water and sea water.     

Stress modulation of cellular metabolic sensors: interaction of stress from temperature and rainfall on the intertidal limpet Cellana toreuma

In the natural environment, organisms are exposed to large variations in physical conditions. Quantifying such physiological responses is, however, often performed in laboratory acclimation studies, in which usually only a single factor is varied. In contrast, field acclimatization may expose organisms to concurrent changes in several environmental variables. The interactions of these factors may have strong effects on organismal function. In particular, rare events that occur stochastically and have relatively short duration may have strong effects. The present experiments studied levels of expression of several genes associated with cellular stress and metabolic regulation in a field population of limpet Cellana toreuma that encountered a wide range of temperatures plus periodic rain events. Physiological responses to these variable conditions were quantified by measuring levels of mRNA of genes encoding heat‐shock proteins (Hsps) and metabolic sensors (AMPKs and Sirtuin 1). Our results reveal high ratios of individuals in upregulation group of stress‐related gene expression at high temperature and rainy days, indicating the occurrence of stress from both prevailing high summer temperatures and occasional rainfall during periods of emersion. At high temperature, stress due to exposure to rainfall may be more challenging than heat stress alone. The highly variable physiological performances of limpets in their natural habitats indicate the possible differences in capability for physiological regulation among individuals. Our results emphasize the importance of studies of field acclimatization in unravelling the effects of environmental change on organisms, notably in the context of multiple changes in abiotic factors that are accompanying global change.     

Community structures of ammonia‐oxidising archaea and bacteria in high‐altitude lakes on the Tibetan Plateau

1. Community structures of planktonic ammonia‐oxidising archaea (AOA) and bacteria (AOB) were investigated for five high‐altitude Tibetan lakes, which could be classified as freshwater, oligosaline or mesosaline, to develop a general view of the AOA and AOB in lakes on the Tibetan Plateau. 2. Based on PCR screening of the ammonia monooxygenase α‐subunit (amoA) gene, AOA were present in 14 out of 17 samples, whereas AOB were detected in only four samples. Phylogenetic analyses indicated that the AOB communities were dominated by a unique monophylogenetic lineage within Nitrosomonas, which may represent a novel cluster of AOB. AOA, on the other hand, were distinct among lakes with different salinities. 3. Multivariate statistical analyses indicated a heterogeneous distribution of the AOA communities among lakes largely caused by lake salinity, whereas the uniform chemical properties within lakes and their geographical isolation may favour relatively homogeneous AOA communities within lakes. 4. Our results suggest a wide occurrence of AOA in Tibetan lakes and provide the first evidence of salinity‐related differentiation of AOA community composition as well as potential geographical isolation of AOA in inland aquatic environments.     

Unusual nonmarine burrows from the Middle Jurassic of Scotland

The Kilmaluag Formation of the Great Estuarine Group (Middle Jurassic) of Scotland represents deposition of mixed carbonate and clastic sediments in a low‐salinity coastal lagoon to floodplain lake setting. Large, unusual trace fossils occur at two horizons within the formation. One type consists of platelike structures about 50 cm in diameter, which are found on wave‐rippled sandstone. These structures, strikingly similar to burrows produced by modern mudskippers, are assigned to fish that shallowly burrowed into the lagoon‐shore sediment.

The second type of burrows, found in brecciated, dolomitic limestones, are pipelike, about 4 to 7 cm in diameter and as much as 50 cm deep. One example has a chamber at the base of the pipe. Although most features of these structures appear similar to modern lungfish burrows, the chamber is most similar to structures produced by modern crayfish. The animal probably burrowed into the moist, mudflat sediment to escape desiccation during seasonal aridity.     

Development of High‐Level Omega‐3 Eicosapentaenoic Acid (EPA) Production from Phaeodactylum tricornutum

Phaeodactylum tricornutum is a lipid‐rich marine diatom that contains a high level of omega‐3 polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA). In an effort to reduce costs for large‐scale cultivation of this microalga, this study first established a New BBM medium (0.3 x strength BBM with only 3% of the initial phosphate level) to replace the traditional F/2 medium. Phaeodactylum tricornutum could grow in extremely low phosphate concentrations (25 µM), without compromising the EPA content. In the presence of sea salts, silicate addition was not necessary for high rate growth, high EPA content, or lipid accumulation in this species. Using urea as the sole nitrogen source tended to increase EPA contents per dry biomass (by 24.7%) while not affecting growth performance. The use of sea salts, rather than just sodium chloride, led to significantly improved biomass yields (20% increase) and EPA contents of total fatty acid (46–52% increase), most likely because it supplied sufficient essential elements such as magnesium. A salinity level of 35 led to significantly higher biomass yields compared with 20, but salinity had no significant influence on EPA content. EPA became the dominant fatty acid with average levels of 51.8% of total fatty acids during the exponential growth phase at 20 ppt in New BBM medium with sea salts.     

施磷和接种AM真菌对玉米耐盐性的影响

在盆栽条件下研究了不同施磷水平（２５,５０,１００,１５０ｍｇ／ｋｇ）,不同盐水平（ＮａＣｌ０,１．２ｇ／ｋｇ）和不同接种ＡＭ真菌处理（接种和不接种）对玉米生长的影响。结果表明,施磷量为５０ｍｇ／ｋｇ时基本满足玉米生长的需要,１．２ｇ／ｋｇ ＮａＣｌ胁迫显著抑制了玉米的生长;施磷明显促进玉米在盐胁迫条件下的生长,施磷水平和接种菌根真菌的交互作用对玉米耐盐性具有显著影响;盐胁迫条件下,接种ＡＭ真菌在     

Dynamic secretion changes in the salt glands of the mangrove tree species Avicennia officinalis in response to a changing saline environment

The specialized salt glands on the epidermis of halophytic plants secrete excess salts from tissues by a mechanism that is poorly understood. We examined the salt glands as putative salt and water bi‐regulatory units that can respond swiftly to altering environmental cues. The tropical mangrove tree species (Avicennia officinalis) is able to grow under fluctuating salinities (0.7–50.0 dS m^?1) at intertidal zones, and its salt glands offer an excellent platform to investigate their dynamic responses under rapidly changing salinities. Utilizing a novel epidermal peel system, secretion profiles of hundreds of individual salt glands examined revealed that these glands could secrete when exposed to varying salinities. Notably, rhythmic fluctuations observed in secretion rates were reversibly inhibited by water channel (aquaporin) blocker, and two aquaporin genes (PIP and TIP) preferentially expressed in the salt gland cells were rapidly induced in response to increasing salt concentration. We propose that aquaporins are involved and contribute to the re‐absorption of water during salt removal in Avicennia officinalis salt glands. This constitutes an adaptive feature that contributes to salt balance of trees growing in saline environments where freshwater availability is limited.