Search

Abstract Isoprene, a volatile hydrocarbon, is typically emitted from the leaves of many plant species. Given its well‐known function in plant growth and defense aboveground, we examined its effects on root physiology. We used isoprene‐emitting (IE) lines and a non‐emitting (NE) line of Arabidopsis and investigated their performance by analyzing root phenotype, hormone levels, transcriptome, and metabolite profiles under both normal and salt stress conditions. We show that IE lines emitted tiny amounts of isoprene from roots and showed an increased root/shoot ratio compared with NE line. Isoprene emission exerted a noteworthy influence on hormone profiles related to plant growth and stress response, promoting root development and salt‐stress resistance. Methyl erythritol 4‐phosphate pathway metabolites, precursors of isoprene and hormones, were higher in the roots of IE lines than in the NE line. Transcriptome data indicated that the presence of isoprene increased the expression of key genes involved in hormone metabolism/signaling. Our findings reveal that constitutive root isoprene emission sustains root growth under saline conditions by regulating and/or priming hormone biosynthesis and signaling mechanisms and expression of key genes relevant to salt stress defense.

Abstract To better understand the salt tolerance of the wild rice, Oryza coarctata, root tissue‐specific untargeted comparative metabolomic profiling was performed against the salt‐sensitive Oryza sativa. Under control, O. coarctata exhibited abundant levels of most metabolites, while salt caused their downregulation in contrast to metabolites in O. sativa. Under control conditions, itaconate, vanillic acid, threonic acid, eicosanoids, and a group of xanthin compounds were comparatively abundant in O. coarctata. Similarly, eight amino acids showed constitutive abundance in O. coarctata. In contrast, under control, glycerolipid abundances were lower in O. coarctata and salt stress further reduced their abundance. Most phospholipids also showed a distribution similar to the glycerolipids. Fatty acyls were however significantly induced in O. coarctata but organic acids were prominently induced in O. sativa. Changes in metabolite levels suggest that there was upregulation of the arachidonic acid metabolism in O. coarctata. In addition, the phenylpropanoid biosynthesis as well as cutin, suberin, and wax biosynthesis were also more enriched in O. coarctata, likely contributing to its anatomical traits responsible for salt tolerance. The comparative variation in the number of metabolites like gelsemine, allantoin, benzyl alcohol, specific phospholipids, and glycerolipids may play a role in maintaining the superior growth of O. coarctata in salt. Collectively, our results offer a comprehensive analysis of the metabolite profile in the roots of salt‐tolerant O. coarctata and salt‐sensitive O. sativa, which confirm potential targets for metabolic engineering to improve salt tolerance and resilience in commercial rice genotypes.

Abstract In the 1980s, Artemia franciscana from San Francisco Bay (SFB) was introduced into Kenyan saltworks, where it has colonized and established stable populations. However, little is known about its biology, particularly with respect to its parental SFB population. This study compared the salinity tolerances of Kenyan (KEN) population, their SFB progenitors and those of Great Salt Lake (GSL) populations. Growth and survival of these A. franciscana populations were evaluated under varying salinity levels in a laboratory set up. A. franciscana nauplii were cultured at a rate of 1 nauplii/mL in 36 Erlenmeyer flasks and fed microalgae (Chaetoceros sp.) at 1.5 × 106 cells/animal/day for 8 days. Survival was evaluated daily and survivors were fixed in individual vials with Lugol solution. The total length of each fixed A. franciscana nauplii specimen was measured under a compound microscope. All populations were susceptible to salinities greater than 100 g/L. Compared with the parental SFB population, the KEN population exhibited significantly reduced survival and growth at 140 g/L, suggesting a narrower salinity tolerance range. These findings underscore the need for further studies focusing on other physiological parameters, abiotic factors and genetic characterization to confirm whether the KEN population is experiencing ecological adaptation. This will contribute to the optimization of Artemia practices in various salinity environments as a result of climate change.

Abstract This study evaluated how light spectrum, salinity, and glucose level affect Spirulina morphology, using response surface methodology (RSM). A full factorial experiment was conducted including three light conditions with different predominant spectral characteristics (“white”: 100% white; “red”: 80% red, 15% blue, and 5% green; and “yellow”: 80% yellow, 15% blue, and 5% green), four NaCl concentrations (0, 5, 15, 30 g/L), and four glucose levels (0, 1.5, 2, 2.5 g/L). Light spectrum conditions and salinity had significant effects on the filament length, spiral diameter, and screw pitch length. Glucose only had a significant effect in terms of the spiral diameter. The maximum filament length (1274 μm; under 30 g/L NaCl and 2.5 g/L glucose), spiral diameter (47 μm; under 1 g/L NaCl and 2 g/L glucose), and screw pitch length (112 μm; under 1 g/L NaCl and 2 g/L glucose) were attained under yellow light. In line with the simulation, more compacted filaments, that is, with a greater diameter (41 μm) and shorter screw pitches (78 μm), are observed under “red” light (4 g/L NaCl and 2.5 g/L glucose). Because longer but compact filaments are desirable for easier harvesting, we recommend a light spectrum that is predominantly red with a NaCl concentration of 5.8 g/L deprived of glucose, for the cost‐effective harvesting of Spirulina biomass.

Abstract Delta Smelt are thought to be on the precipice of extinction. Studies that examine how this endangered species responds to environmental change are important to informing conservation efforts. In the wild, Delta Smelt are likely to encounter wide variation in the salinity of their environment that is influenced by both natural and anthropogenic factors. We examined how salinity affects the group structure of Delta Smelt across multiple diel cycles. We found that the interaction between salinity (0, 5, 10 and 15 ppt) and time period (Day 1, Night 1, Day 2 and Night 2) influenced their spatial distribution within a group. Specifically, Delta Smelt were less dispersed, more cohesive and more homogenously distributed in saline water than in freshwater, but only on the first day, and this difference was not statistically significant. We also found that Delta Smelt were significantly less dispersed, more cohesive and more homogenous during the day than at night. Thus, Delta Smelt appear to behaviourally adapt to the initial stress of acute salinity exposure, which may mirror their physiological ability to acclimate to such conditions. Additionally, Delta Smelt group structure appears to shift depending on the time of day, suggesting that diel timing may influence conspecific interactions and should be considered in the experimental design of future studies. These findings further our understanding of how Delta Smelt behaviourally respond to environmental and diel variation.

Abstract Barley is one of the world's earliest domesticated crops, which is widely used for beer production, animal feeding, and health care. Barley seed germination, particularly in increasingly saline soils, is key to ensure the safety of crop production. However, the mechanism of salt‐affected seed germination in barley remains elusive. Here, two different colored barley varieties were used to independently study the regulation mechanism of salt tolerance during barley seed germination. High salinity delays barley seed germination by slowing down starch mobilization efficiency in seeds. The starch plate test revealed that salinity had a significant inhibitory effect on α‐amylase activity in barley seeds. Further, NaCl treatment down‐regulated the expression of Amy1, Amy2 and Amy3 genes in germinated seeds, thereby inhibiting α‐amylase activity. In addition, the result of embryogenic culture system in vitro showed that the shoot elongation of barley was significantly inhibited by salt stress. These findings indicate that it is a feasible idea to study the regulation mechanism of salinity on barley seed germination and embryo growth from the aspect of starch‐related source‐sink communication.

Abstract Marine biodiversity consists of a complex network of organisms responsible for keeping the ecosystem's balance. Fungi are an understudied group of organisms despite their recognized importance for ecosystem processes and diversity. How fungi respond to environmental change remains poorly understood, especially in marine benthic habitats. The Baltic Sea is a brackish coastal ecosystem with steep environmental gradients in a relatively limited geographical area and is therefore a particularly good system to investigate the impact of different abiotic factors on benthic fungal diversity. This study used environmental DNA (eDNA) metabarcoding to analyze the spatial dynamics of benthic fungal diversity in the Baltic Sea and quantify the environmental drivers that shape these dynamics. Based on 59 stations spreading over 1145 km the results showed that benthic fungal communities were dominated by the phylum Chytridiomycota, and the fungal species Alphamyces chaetifer and Operculomyces laminatus from this phylum were the main drivers of the community structure dissimilarities observed between regions. Water depth and salinity were the main predictors of the benthic fungal community composition. The impact of nutrient availability was also significant, possibly related to the known role of Chytridiomycota species such as A. chaetifer and O. laminatus in nutrient cycling. Our results indicate that the benthic fungal diversity of the Baltic Sea is shaped by salinity gradients and nutrient availability and highlights that the current fungal biodiversity is at risk of species shift or decline with predicted changes in salinity due to climate change and intensified eutrophication.

Abstract Introduction Soil salinization is a major abiotic stress that imposes high osmotic stress on plant growth, thereby limiting crop productivity. It also acts as an environmental filter for microbes, impacting associated ecosystem services and functions. Agricultural practices such as cover cropping can help mitigate the negative impacts of soil salinity. However, our knowledge of how cover cropping and salinity influence soil microbiome diversity and complexity is limited. Materials & Methods Using amplicon sequencing, metagenomics, and network analysis, we aimed to determine if cover cropping can be effective in maintaining microbiome complexity and functioning in salinity‐affected soils. We conducted a field study to determine the soil microbial properties over four locations with salinity (saline: SS, and nonsaline: NS) and cover cropping (cover‐cropped: CC, and no cover‐cropped: NC) treatments. We hypothesized that microbial diversity and complexity will be lower in saline as compared to nonsaline soils, and the reduction can be countered by inclusion of cover crops. Results Our results found a significant effect of salinity on the clustering of bacterial communities in soil. However, cover cropping increased bacterial and fungal alpha diversity. Cover cropping increased soil microbial network complexity under both saline and nonsaline conditions. Most of the keystone taxa were members of the order Thermomicrobiales, which are known to enhance stress tolerance in plants. Metagenomics revealed higher activities of genes related to transcription and folate metabolism in saline‐cover crop treatments. Conclusion Our results identify key microbial players under salinity stress and highlight the potential of using cover crops to mitigate the negative effect of salinity on soil microbiomes, which can facilitate sustainable productivity in saline agroecosystems.

Abstract Maximum sea surface salinity (SSS) anomalies are found in the central Pacific during the eastern Pacific El Niño (EPEN) and located further westward during the central Pacific El Niño (CPEN), but whether these differences affect event strengths is unclear. By performing ocean general circulation model experiments via modifying freshwater flux anomalies, we find salinity effects on surface warming during both types are highly sensitive to zonal locations of SSS anomalies, with the strongest warming induced by the SSS anomalies near the international dateline. Further analysis reveals that vertical mixing and entrainment dominate this temperature sensitivity, with the strongest response to SSS anomalies occurring in the central Pacific. The central‐Pacific SSS anomalies increase EPEN warming by 0.15°C while the westward‐located SSS anomalies make little contribution to CPEN warming. Therefore, the distinct zonal structures of SSS anomalies facilitate stronger EPEN than the CPEN, increasing their difference in intensity by about 10%.

Abstract Introduction Several water quality indices exist to evaluate irrigation water quality (IWQ), but they have some limitations. This study attempted to develop a new Overall Irrigation Water Quality Index (Overall IWQIndex) using a rational subindex that is flexible enough and updated to signify irrigation water suitability. It considered the maximum verified desirable and permissible value of parameters, including the hazard class, a modified rating system of parameters in each hazard class, and diversified water parameters that have affected the soil and plants. Materials and Methods A total of 40 calcite‐type groundwater samples were analyzed to evaluate the IWQ using the proposed Overall IWQIndex, some IWQ parameters, and different diagram‐based statistical methods. Results The study results were correlated with each other critically, and finally, the suitability for IWQ was determined. The results revealed that the samples of the postmonsoon and premonsoon felt under the ‘good’ and ‘excellent’ categories, respectively. Conclusion The study developed an indexing model that is easy to compute, rationalize and deliver accurate information on the suitability of irrigation water.

Abstract How subsurface microbial life changed at the bottom of the kilometers‐deep (hypo) Critical Zone in response to evolving surface conditions over geologic time is an open question. This study investigates the burial and exhumation, biodegradation, and fluid circulation history of hydrocarbon reservoirs across the Colorado Plateau as a window into the hypo‐Critical Zone. Hydrocarbon reservoirs, in the Paradox and Uinta basins, were deeply buried starting ca. 100 to 60 Ma, reaching temperatures >80–140°C, likely sterilizing microbial communities present since the deposition of sediments. High salinities associated with evaporites may have further limited microbial activity. Upward migration of hydrocarbons from shale source rocks into shallower reservoirs during maximum burial set the stage for microbial re‐introduction by creating organic‐rich “hot spots.” Denudation related to the incision of the Colorado River over the past few million years brought reservoirs closer to the surface under cooler temperatures, enhanced deep meteoric water circulation and flushing of saline fluids, and likely re‐inoculated more permeable sediments up to several km depth. Modern‐ to paleo‐hydrocarbon reservoirs show molecular and isotopic evidence of anaerobic oxidation of hydrocarbons coupled to bacterial sulfate reduction in areas with relatively high SO4‐fluxes. Anaerobic oil biodegradation rates are high enough to explain the removal of at least some portion of postulated “supergiant oil fields” across the Colorado Plateau by microbial activity over the past several million years. Results from this study help constrain the lower limits of the hypo‐Critical Zone and how it evolved over geologic time, in response to changing geologic, hydrologic, and biologic forcings.

Abstract Salinity is increasingly considered as a major environmental issue, which threatens agricultural production by decreasing yield traits of crops. Seed priming is a useful and cost‐effective technique to alleviate the negative effects of salinity and to enable a fast and uniform germination. In this context, we quantified the effects of priming with gibberellic acid (GP), calcium chloride (CP), and mannitol (MP) on seed germination of three bread wheat cultivars and investigated their response when grown at high salinity conditions (200 mM NaCl). Salt exposure strongly repressed seed imbibition and germination potential and extended germination time, whereas priming enhanced uniformity and seed vigor. Seed preconditioning alleviated the germination disruption caused by salt stress to varying degrees. Priming mitigating effect was agent‐dependent with regard to water status (CP and MP), ionic imbalance (CP), and seed reserve mobilization (GP). Na+ accumulation in seedling tissues significantly impaired carbohydrate and protein mobilization by inhibiting amylase and proteases activities but had lesser effects on primed seeds. CP attenuated ionic imbalance by limiting sodium accumulation. Gibberellic acid was the most effective priming treatment for promoting the germination of wheat seeds under salt stress. Moreover, genotypic differences in wheat response to salinity stress were observed between varieties used in this study. Ardito, the oldest variety, seems to tolerate better salinity in priming‐free conditions; Aubusson resulted the most salt‐sensitive cultivar but showed a high germination recovery under priming conditions; Bologna showed an intermediate behavior.

Abstract Fluids in sedimentary basins exert a crucial influence on various geological phenomena including natural resource formation. Worldwide drilling projects have revealed that the salinity of sedimentary basinal fluids generally increases with depth, irrespective of lithology, age of sediments, or the presence of a halite bed. However, how these vertical salinity variations are produced and what controls the salinity remain unclear. This work examines a new hypothesis that downward‐increasing salinity variations are a natural outcome of the constant chemogravitational potential condition. In a static environment, the salinity is distributed such that the chemogravitational potential of the solute is constant with depth. Once formed, such a distribution would be maintained because no further migration of the solute would occur. To test the hypothesis, a constant chemogravitational potential distribution model was constructed for NaCl–H2O fluids in the sediment column, and NaCl content at each depth was calculated. The results showed that NaCl content monotonically increases with depth, and the variations are similar to the trend of measured data. However, the data were not necessarily completely reproduced by the model, and deviated in some parts from the calculated profile. Such deviation may indicate fluxing of external fluid occurring in these parts, as the constant chemogravitational potential is vulnerable to an advective flow. Therefore, it is proposed that the constant chemogravitational potential condition is a possible endmember theory, influencing natural salinity variations in a static environment.

Abstract Stable isotopes of oxygen (δ18O) in seawater reflect the combined influences of ocean circulation and atmospheric moisture balance. However, it is difficult to disentangle disparate ocean and atmosphere influences on modern seawater δ18O values, partly because continuous time series of seawater δ18O are rare. Here we present a nearly nine‐year, continuous record of seawater δ18O values from the Galápagos. Seawater δ18O values faithfully track sea surface salinity and salinity along the equator at 50 m depth. Zonal current velocity within the Equatorial Undercurrent (EUC), directly west of the Galápagos, is strongly correlated with Galápagos surface seawater δ18O values with a 1‐month lag. Reconstructions of Galápagos seawater δ18O values could thus provide a window into past variations in the strength of the EUC, an important influence on large‐scale tropical Pacific climate.

Abstract Plant scientists and farmers are facing major challenges in providing food and nutritional security for a growing population, while preserving natural resources and biodiversity. Moreover, this should be done while adapting agriculture to climate change and by reducing its carbon footprint. To address these challenges, there is an urgent need to breed crops that are more resilient to suboptimal environments. Huge progress has recently been made in understanding the physiological, genetic and molecular bases of plant nutrition and environmental responses, paving the way towards a more sustainable agriculture. In this review, we present an overview of these progresses and strategies that could be developed to increase plant nutrient use efficiency and tolerance to abiotic stresses. As illustrated by many examples, they already led to promising achievements and crop improvements. Here, we focus on nitrogen and phosphate uptake and use efficiency and on adaptation to drought, salinity and heat stress. These examples first show the necessity of deepening our physiological and molecular understanding of plant environmental responses. In particular, more attention should be paid to investigate stress combinations and stress recovery and acclimation that have been largely neglected to date. It will be necessary to extend these approaches from model plants to crops, to unravel the relevant molecular targets of biotechnological or genetic strategies directly in these species. Similarly, sustained efforts should be done for further exploring the genetic resources available in these species, as well as in wild species adapted to unfavourable environments. Finally, technological developments will be required to breed crops that are more resilient and efficient. This especially relates to the development of multiscale phenotyping under field conditions and a wide range of environments, and use of modelling and big data management to handle the huge amount of information provided by the new molecular, genetic and phenotyping techniques.

Abstract Lacustrine non‐skeletal carbonates exhibit a diversity of petrographies due to interactions between physico‐chemical and biologically influenced mechanisms. Despite the suggestion that evaporative concentration was involved in the formation of spherulite and shrubby‐bearing carbonate successions in the Pre‐Salt Cretaceous alkaline lakes of the South Atlantic, no consensus exists about the water chemistries promoting these exotic mineral textures. In this work, an experimental approach was developed to evaluate how changes in salinity (NaCl) and biopolymer concentrations (alginic acid) impact calcite growth dynamics from saline and alkaline synthetic solutions. Hydrochemical and petrographical data from selected modern saline/alkaline environments were compared with experimental datasets to further estimate how the underlying (bio)chemical conditions and lake locations probably converge to allow the formation of calcite spherulite grains in evaporitic settings. Spherulitic calcite from Recent saline lakes and experiments arise from waters with moderate to high [Calcium]/[Alkalinity] ratios ([Ca]/[Alk]) rather than in calcium‐depleted and alkaline‐rich environments which tend to produce single‐crystal calcites during abiotic water mixing or lake evaporation. This observation is consistent with the assembly of polycrystalline textures being a kinetically controlled feature, forced by remarkably high rates of nucleation. Also, the data analysed do not support a causative relationship between evaporite‐driven salinity fluctuations and the preferential formation of spherulites, shrubs or their intermediate textures. Ubiquitous in saline lakes, organic substances can lower the kinetic thresholds for spherulitic calcite aggregation while microbial photosynthesis can also raise pH, altogether enhancing calcite supersaturation and promoting spherulite formation in waters with moderate‐high [Ca]/[Alk] ratios and high salinities. Localised observations of abiotic spherulites in Recent soda lakes can occur in restricted mixing zones where [Ca]/[Alk] ratios are enhanced. This work highlights the roles of concentration regimes associated with biopolymers and microbial metabolism against the background salinity fluctuations in determining the morphological and textural transitions in lacustrine carbonate minerals.

Abstract Evolutionary theory predicts that selection will favor phenotypic plasticity in sperm traits that maximize fertilization success in dynamic fertilization environments. In species with external fertilization, osmolality of the fertilization medium is known to play a critical role in activating sperm motility, but evidence for osmotic‐induced sperm plasticity is limited to euryhaline fish and marine invertebrates. Whether this capacity extends to freshwater taxa remains unknown. Here, we provide the first test for plasticity in sperm‐motility activation in response to osmotic environment in an anuran amphibian. Male common eastern froglets (Crinia signifera) were acclimated to either low (0 mOsmol kg−1) or high (50 mOsmol kg−1) environmental osmolality, and using a split‐sample experimental design, sperm were activated across a range of osmolality treatments (0, 25, 50, 75, 100, and 200 ± 2 mOsmol kg−1). Unexpectedly, there was no detectable shift in the optimal osmolality for sperm‐motility activation after approximately 13 weeks of acclimation (a period reflecting the duration of the winter breeding season). However, in both the low and high acclimation treatments, the optimal osmolality for sperm‐motility activation mirrored the osmolality at the natural breeding site, indicating a phenotypic match to the local environment. Previously it has been shown that C. signifera display among‐population covariation between environmental osmolality and sperm performance. Coupled with this finding, the results of the present study suggest that inter‐population differences reflect genetic divergence and local adaptation. We discuss the need for experimental tests of osmotic‐induced sperm plasticity in more freshwater taxa to better understand the environmental and evolutionary contexts favoring adaptive plasticity in sperm‐motility activation.

Rhizobacteria play a crucial role in plant growth and yield, stimulating primary production and improving stress resistance. Climate change has several consequences worldwide that affect arable land and agriculture. Studies on plant-soil-microorganism interactions to enhance plant productivity and/or resistance to abiotic stress may open new perspectives. This strategy aims to make agricultural-relevant plant species able to complete their biological cycle in extreme soils with the help of inoculated or primed plant growth-promoting rhizobacteria (PGPR). We provide an overview of the evolution of interest in PGPR research in the last 30 years through: (i) a quantitative search on the Scopus database; (ii) keyword frequencies and clustering analysis, and (iii) a keyword network and time-gradient analysis. The review of scientific literature on PGPR highlighted an increase in publications in the last 15 years, and a specific time gradient on subtopics, such as abiotic stresses. The rise in PGPR as a keyword co-occurring with salinity and drought stresses aligns with the growing number of papers from countries directly or partly affected by climate change. The study of PGPR, its features, and related applications will be a key challenge in the next decades, considering climate change effects on agriculture. The increased interest in PGPR leads to deeper knowledge focused specifically on researching agriculturally sustainable solutions for soils affected by salinity and drought., (© 2024 Wiley‐VCH GmbH. Published by John Wiley & Sons Ltd.)

Abstract Soil salinity is a major issue limiting efficient crop production. Seed priming with nanomaterials (nanopriming) is a cost‐effective technology to improve seed germination under salinity; however, the underlying mechanisms still need to be explored. Here, polyacrylic acid coated nanoceria (cerium oxide nanoparticles) (PNC, 9.2 nm, −38.7 mV) are synthesized and characterized. The results show that under salinity, PNC priming significantly increases rapeseed shoot length (41.5%), root length (93%), and seedling dry weight (78%) compared to the no‐nanoparticle (NNP) priming group. Confocal imaging results show that compared with NNP group, PNC priming significantly reduces reactive oxygen species (ROS) level in leaf (94.3% of H2O2, 56.4% of •O2−) and root (38.4% of H2O2, 41.3% of •O2−) of salt stressed rapeseed seedlings. Further, the results show that compared with the NNP group, PNC priming not only increases salicylic acid (SA) content in shoot (51.3%) and root (78.4%), but also upregulates the expression of SA biosynthesis related genes in salt stressed rapeseed. Overall, PNC nanopriming improved rapeseed salt tolerance is associated with both the increase of ROS scavenging ability and the increase of salicylic acid. The results add more information to understand the complexity of mechanisms behind nanoceria priming improved plant salt tolerance.

Abstract The effect of low salinity levels on byssal re‐attachment behavior in Pteria penguin juveniles was observed in the laboratory. Juvenile pearl oysters were submerged in seawater blended to 8.0, 12.0, 16.0, 20.0, 24.0, 28.0, and 32.0 salinity levels for a period of 48 hr. The sub‐lethal salinity level was greater than 20.0 psu. Although salinity levels of 20.0 and 24.0 psu did not affect the oyster survival, the observed byssogenesis activity was significantly reduced and locomotion activity was delayed. Description of the effects of low salinity levels on the byssal re‐attachment behavior of P. penguin juveniles provides a foundation for the design of more complex experiments and approaches to further the exploration and development of improved pearl production techniques.

Abstract Lysine cannot be synthesized by the human body, and it is, therefore, an indispensable amino acid in the human that must be consumed in adequate amounts to prevent disease. Unfortunately, lysine is not abundant in many important food sources such as rice grains. Efforts to fortify rice and other monocotyledonous crops with high lysine have proved to be challenging because of their effects on plant growth. The present study was designed to avoid the problems that are often encountered in engineering lysine metabolism. We generated different over‐expression constructs for the key anabolic enzyme, dihydrodipicolinate synthase (DHDPS and cdapA) and knockdown (KD) constructs for the catabolic enzyme—lysine ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH), with expression under the control of either the CaMV35S promoter or the endosperm‐specific glutelinD1 promoter. The use of the endosperm‐specific promoter together with the lysine feedback‐insensitive cdapA for over‐expression provides distinct advantages, as does silencing of LKR/SDH under the control of this promoter. Rice plants produced by over‐expressing cdapA together with silencing of LKR/SDH showed a 58% increase in grain lysine content, as well as higher amounts of total seed protein levels. Moreover, the transgenic seedlings were more tolerant to salinity. These results demonstrate that it is possible to generate high lysine stress‐tolerant rice varieties, which have the potential to reduce the need for dietary supplementation.

Abstract Estuaries of major rivers provide important stopover habitat for migratory birds throughout the world. These estuaries experience large amounts of freshwater inputs from spring runoff. Understanding how freshwater inputs affect food supply for migrating birds, and how birds respond to these changes will be essential for effective conservation of critical estuarine habitats. We estimated trends over time in counts of Western Sandpiper (Calidris mauri) and Pacific Dunlin (Calidris alpina pacifica) during northward migration on the Fraser River estuary, British Columbia, Canada, where shorebirds feed extensively on intertidal biofilm and invertebrates. We also examined whether counts were correlated with a suite of environmental variables related to local conditions (precipitation, temperature, wind speed and direction, solar radiation, tidal amplitude, and discharge rates from the Fraser River) during a total of 540 surveys from 1991 to 2019. Counts of Western Sandpiper declined ~54% (−2.0% per annum) over the entire study period, and 23% from 2009 to 2019 (−0.9% per annum). Counts of Pacific Dunlin did not show a statistically significant change over the study period. Counts of shorebirds were lower when discharge from the Fraser River was high, which we propose results from a complex interaction between the abrupt changes in salinity and the estuarine food web related to the quantity or quality of intertidal biofilm. Counts were also higher when tidal amplitude was lower (neap tides), potentially related to longer exposure times of the mudflats than during spring tides. Effects of wind are likely related to birds delaying departure from the stopover site during unfavorable wind conditions. The negative trend in migrating Western Sandpipers is consistent with declines in nonbreeding areas as observed in Christmas Bird Counts. Understanding causes of population change in migratory shorebirds highlights the need for research on mechanistic pathways in which freshwater inputs affect food resources at estuarine stopovers.

Abstract Plasticity in salt tolerance can be crucial for successful biological invasions of novel habitats by marine gastropods. The intertidal snail Batillaria attramentaria, which is native to East Asia but invaded the western shores of North America from Japan 80 years ago, provides an opportunity to examine how environmental salinity may shape behavioral and morphological traits. In this study, we compared the movement distance of four B. attramentaria populations from native (Korea and Japan) and introduced (United States) habitats under various salinity levels (13, 23, 33, and 43 PSU) during 30 days of exposure in the lab. We sequenced a partial mitochondrial CO1 gene to infer phylogenetic relationships among populations and confirmed two divergent mitochondrial lineages constituting our sample sets. Using a statistical model‐selection approach, we investigated the effects of geographic distribution and genetic composition on locomotor performance in response to salt stress. Snails exposed to acute low salinity (13 PSU) reduced their locomotion and were unable to perform at their normal level (the moving pace of snails exposed to 33 PSU). We did not detect any meaningful differences in locomotor response to salt stress between the two genetic lineages or between the native snails (Japan vs. Korea populations), but we found significant locomotor differences between the native and introduced groups (Japan or Korea vs. the United States). We suggest that the greater magnitude of tidal salinity fluctuation at the US location may have influenced locomotor responses to salt stress in introduced snails.

Abstract Hybrids of a single pair of parent species can be much more common in some geographical regions than in others. The reasons for this are not well understood, but could help explain processes such as species diversification or the range expansion of invasive hybrids. The widespread cattails Typha latifolia and T. angustifolia seldom hybridize in some parts of their range, but in other areas produce the dominant hybrid T. × glauca. We used a combination of field and greenhouse experiments to investigate why T. × glauca has invaded wetlands in the Laurentian Great Lakes region of southern Ontario, Canada, but is much less common in the coastal wetlands of Nova Scotia (NS) in eastern Canada. One potentially important environmental difference between these two regions is salinity. We therefore tested three hypotheses: (1) T. latifolia and T. angustifolia in NS are genetically incompatible; (2) the germination or growth of T. × glauca is reduced by salinity; and (3) T. latifolia, a main competitor of T. × glauca, is locally adapted to saline conditions in NS. Our experiments showed that NS T. latifolia and T. angustifolia are genetically compatible, and that saline conditions do not impede growth of hybrid plants. However, we also found that under conditions of high salinity, germination rates of hybrid seeds were substantially lower than those of NS T. latifolia. In addition, germination rates of NS T. latifolia were higher than those of Ontario T. latifolia, suggesting local adaptation to salinity in coastal wetlands. This study adds to the growing body of literature which identifies the important roles that local habitat and adaptation can play in the distributions and characteristics of hybrid zones.

Abstract Functional traits are becoming more common in the analysis of marine zooplankton community dynamics associated with environmental change. We used zooplankton groups with common functional properties to assess long‐term trends in the zooplankton caused by certain environmental conditions in a highly eutrophicated gulf. Time series of zooplankton traits have been collected since the 1960s in the Gulf of Riga, Baltic Sea, and were analyzed using a combination of multivariate methods (principal coordinate analysis) and generalized additive models. One of the most significant changes was the considerable increase in the amount of the zooplankton functional groups (FGR) in coastal springtime communities, and dominance shifts from more complex to simpler organism groups—cladocerans and rotifers. The results also show that functional trait organism complexity (body size) decreased considerably due to cladoceran and rotifer increase following elevated water temperature. Salinity and oxygen had negligible effects on the zooplankton community.

Abstract The skeletons of massive corals inhabiting tropical and subtropical oceans grow over centuries. The chemical and isotopic compositions of their skeletons reflect changes in the marine environment and provide an archive of sea surface temperature (SST) and salinity at a high temporal resolution spanning decades to centuries. Stable oxygen isotope ratios in coral skeletons (δ18Oc) are an excellent proxy for SST and the stable oxygen isotopic composition in seawater (δ18Osw). Variations in δ18Osw serve as a hydrological proxy and are routinely estimated by subtracting the SST component from δ18Oc. The SST component of δ18Oc is inferred from coral Sr/Ca (SST proxy). Both Sr/Ca and δ18Oc are converted to SST units based on Sr/Ca‐ and (δ18Oc–δ18Osw)‐SST calibrations. However, the exact slope values of the Sr/Ca‐SST and (δ18Oc–δ18Osw)‐SST calibrations are challenging to assess, which hampers the reliable estimation of SST, δ18Osw, and their uncertainties. Here, we present a simple Monte Carlo approach to estimate variations in SST and δ18Osw together with their confidence intervals. Our approach improves on previous error propagation methods by including intercolonial differences of calibration slopes in addition to analytical errors. In addition, Monte Carlo experiments using adjusted errors suggest that uncertainties in the calibration slopes have a minor influence on estimates of SST and δ18Osw.

Abstract The overall mean levels of different environmental variables are changing rapidly in the present Anthropocene, in some cases creating lethal conditions for organisms. Under this new scenario, it is crucial to know whether the adaptive potential of organisms allows their survival under different rates of environmental change. Here, we used an eco‐evolutionary approach, based on a ratchet protocol, to investigate the effect of environmental change rate on the limit of resistance to salinity of three strains of the toxic cyanobacterium Microcystis aeruginosa. Specifically, we performed two ratchet experiments in order to simulate two scenarios of environmental change. In the first scenario, the salinity increase rate was slow (1.5‐fold increase), while in the second scenario, the rate was faster (threefold increase). Salinity concentrations ranging 7–10 gL‐1 NaCl (depending on the strain) inhibited growth completely. However, when performing the ratchet experiment, an increase in salinity resistance (9.1–13.6 gL‐1 NaCl) was observed in certain populations. The results showed that the limit of resistance to salinity that M. aeruginosa strains were able to reach depended on the strain and on the rate of environmental change. In particular, a higher number of populations were able to grow under their initial lethal salinity levels when the rate of salinity increment was slow. In future scenarios of increased salinity in natural freshwater bodies, this could have toxicological implications due to the production of microcystin by this species.

Abstract Populations may respond to environmental heterogeneity via evolutionary divergence or phenotypic plasticity. While evolutionary divergence occurs through DNA sequence differences among populations, plastic divergence among populations may be generated by changes in the epigenome. Here, we present the results of a genome‐wide comparison of DNA methylation patterns and genetic structure among four populations of Eastern oyster (Crassostrea virginica) in the northern Gulf of Mexico. We used a combination of restriction site‐associated DNA sequencing (RADseq) and reduced representation bisulfite sequencing (RRBS) to explore population structure, gene‐wide averages of FST, and DNA methylation differences between oysters inhabiting four estuaries with unique salinity profiles. This approach identified significant population structure despite a moderately low FST (0.02) across the freshwater boundary of the Mississippi river, a finding that may reflect recent efforts to restore oyster stock populations. Divergence between populations in CpG methylation was greater than for divergence in FST, likely reflecting environmental effects on DNA methylation patterns. Assessment of CpG methylation patterns across all populations identified that only 26% of methylated DNA was intergenic; and, only 17% of all differentially methylated regions (DMRs) were within these same regions. DMRs within gene bodies between sites were associated with genes known to be involved in DNA damage repair, ion transport, and reproductive timing. Finally, when assessing the correlation between genomic variation and DNA methylation between these populations, we observed population‐specific DNA methylation profiles that were not directly associated with single nucleotide polymorphisms or broader gene‐body mean FST trends. Our results suggest that C. virginica may use DNA methylation to generate environmentally responsive plastic phenotypes and that there is more divergence in methylation than divergence in allele frequencies.

Abstract Invasive species may quickly colonize novel environments, which could be attributed to both phenotypic plasticity and an ability to locally adapt. Reproductive traits are expected to be under strong selection when the new environment limits reproductive success of the invading species. This may be especially important for external fertilizers, which release sperm and eggs into the new environment. Despite adult tolerance to high salinity, the invasive fish Neogobius melanostomus (round goby) is absent from fully marine regions of the Baltic Sea, raising the possibility that its distribution is limited by tolerance during earlier life stages. Here, we investigate the hypothesis that the spread of N. melanostomus is limited by sperm function in novel salinities. We sampled sperm from two invasion fronts with higher and lower salinities in the Baltic Sea and tested them across a range of salinity levels. We found that sperm velocity and percentage of motile sperm declined in salinity levels higher and lower than those currently experienced by the Baltic Sea populations, with different performance curves for the two fronts. Sperm velocity also peaked closer to the home salinity conditions in each respective invasion front, with older localities showing an increased fit to local conditions. By calculating how the sperm velocity has changed over generations, we show this phenotypic shift to be in the range of other fish species under strong selection, indicating ongoing local adaptation or epigenetic acclimation to their novel environment. These results show that while immigrant reproductive dysfunction appears to at least partly limit the distribution of invasive N. melanostomus in the Baltic Sea, local adaptation to novel environments could enable future spread beyond their current boundaries.

Abstract In the saline depressions (Sebkhas) of Tunisia, Sulla carnosa expresses anarchic distribution, sometimes in association with halophytes sometimes individually. In order to explain this distribution, we investigated the effects of salinity on seed germination, the osmotic and toxic limiting factors, and the importance of some stimulating agents (priming agents) in the improvement of the tolerance to salinity at the germinating stage. A study was conducted on seeds harvested from the natural biotope Sebkha d'El Kelbia (35°50′34″N, 10°16′18″E), and an increasing concentration of NaCl (0, 5, 10, 15, and 20 g L−1) was applied. Some priming agents were used to propose efficient, rapid, and low‐cost tools to improve the seed germination and tolerance of Sulla carnosa (Desf.) in saline depression. Salinity stress significantly decreased germination capacity and rate and delayed its initiation and maximum. Until 15‐g L−1 NaCl, the most limiting factor of seed germination is the osmotic effect. At 20‐g L−1 NaCl, the toxic effect dominates, and germination is irreversibly inhibited. Some priming agents have shown their efficiency in improving the germination capacity at 10‐g L−1 NaCl and conferring a salt tolerance of up to 15‐g L−1 NaCl.

Abstract Coastal and estuarine systems provide critical shark habitats due to their relatively high productivity and shallow, protected waters. The young (neonates, young‐of‐the‐year, and juveniles) of many coastal shark species occupy a diverse range of habitats and areas where they experience environmental variability, including acute and seasonal shifts in local salinities and temperatures. Although the location and functioning of essential shark habitats has been a focus in recent shark research, there is a paucity of data from the South Pacific. In this study, we document the temporal and spatial distribution, age class composition, and environmental parameters of young bull sharks (Carcharhinus leucas) in the Rewa, Sigatoka, and Navua Rivers, Fiji's three largest riverine systems. One hundred and seventy‐two young bull sharks were captured in fisheries‐independent surveys from January 2016 to April 2018. The vast majority of the captures were neonates. Seasonality in patterns of occurrence of neonate individuals suggests a defined parturition period during summer. Environmental parameters between the Rewa and the Sigatoka River differed significantly, as did the recorded young bull sharks abundance. According to the surveys, young bull sharks occur in all three rivers with the Rewa River likely representing essential habitat for newly born bull sharks. These results enhance the understanding of bull shark ecology in Fiji and provide a scientific basis for the implementation of local conservation strategies that contribute to the protection of critical habitats.

Abstract Microbiological activity can exert a substantial influence on carbonate mineral precipitation, but linking specific microbiological processes to carbonate minerals in an environmental setting is complex, as both abiotic and biotic factors ultimately influence carbonate mineral precipitation. The coral atoll of Kiritimati, Republic of Kiribati (1.9°N, 157.4°W), in the central tropical Pacific Ocean, contains hundreds of shallow water brackish to hypersaline lakes that contain a range of carbonate and evaporite minerals. Previous studies of Kiritimati lakes have investigated the microbial communities of finely laminated microbial mats and associated microbialites found in several of the more hypersaline lakes on the island. However, the microbial communities of the more brackish lakes are unknown. These brackish lakes precipitate metres of fine‐grained carbonate muds, which are useful for palaeoenvironmental reconstruction. Here, the relationships between carbonate abundance, mineralogy, water chemistry, and bacterial and archaeal communities are investigated in a suite of brackish to hypersaline lakes (8.7‐190 ppt) on Kiritimati. Next generation 16S rRNA gene sequencing of bacteria and archaea indicate that brackish lake sediments contain distinct microbial communities. In relation to carbonate precipitation, the relative abundance of Cyanobacteria, Choloroflexi and Deltaproteobacteria is greater in the brackish lake sediments, suggesting photosynthesis and sulphate reduction associated with these taxa may strongly influence alkalinity and carbonate precipitation in brackish lakes. The presence of dolomite in certain hypersaline lakes also coincided with the presence of a methanogenic family, indicating that methogenesis may contribute to dolomite precipitation in these lakes.

Abstract In the IODP 372A proposal, working hypotheses used with respect to actively deforming gas hydrate‐bearing landslides were based on an initial calculation considering gas hydrate to occur in fresh water. This initial inaccuracy leads to predict the base of methane hydrate stability zone (MHSZ) to be at around 162 m below the seafloor (mbsf) at site U1517 while it is expected to be between 85 and 128 mbsf. It is most interesting that important negative chloride anomalies were measured well below the theoretical MHSZ without direct evidence of the presence of gas hydrate. These anomalies are usually a strong indication of gas hydrate occurrence. This initial inaccurate hypothesis provides the opportunity to evaluate the effectiveness of the indirect salinity detection method to quantify gas hydrate.

Abstract Climate change is projected to increase the frequency of extreme drought events, which can have dramatic consequences for ecosystems. Extreme drought may interact with other stressors such as invasion by non‐native species, yet little research has explored these dynamics. Here, we examine the physical mechanisms and temporal scale underlying a dieback of an invasive non‐native plant, Lepidium latifolium, in tidal salt marshes of the San Francisco Bay, California, USA, during an extreme, multi‐year drought occurring from 2012 to 2015. Using generalized additive mixed models (GAMMs), we explored the relationship between eight years of estuarine salinity data and five years of L. latifolium density data from three marshes spanning a gradient of salinity across the San Francisco Bay. We found a significant time‐lagged (3 yr) effect of estuarine salinity on L. latifolium density, with high salinities preceding reductions in L. latifolium densities and low salinities preceding increases. The most dramatic change in stem density, a 54% reduction in 2015, was preceded by a salinity increase of 43% from 2011 to 2012. We found the L. latifolium decline was driven by impacts on mature, rather than young, plants. Additionally, we tested the importance of local precipitation in driving L. latifolium densities in a one‐season rain exclusion experiment. We found 100% exclusion of precipitation during one rainy season (January–mid‐May) did not have a significant impact on densities of mature stands of L. latifolium. Our finding that estuarine salinity was a key driver of L. latifolium invasion dynamics suggests sea level rise, like extreme drought, may hinder L. latifolium invasion, as it will also raise estuarine salinities. Further, our study highlights the importance of temporal lags in understanding climate change impacts on biological invasions, which has received very little study to date.

Abstract Exacerbated inundations and saltwater intrusions due to sea‐level rise can significantly alter the ecology of low‐lying coastal drylands by affecting their nutrient cycling and productivity. During the present study, controls on production and consumption of nitrogen in soils of semiarid tropical climate with different levels of vegetation–salinity–moisture condition were investigated using 15N isotope dilution experiments. For this purpose, soils were collected from five land types including two in salt flat and one each in grassland (GL), wetland (WL), and an agricultural field. Soils with no vegetation, high salinity, and high moisture (salt flats) showed significant decline in gross production of nitrogen (mineralization rate: 0.21 ± 0.10 mg N·kg−1·d−1; nitrification rate: 0.27 ± 0.17 mg N·kg−1·d−1) compared to soils with vegetation, low salinity, and low moisture (GL, WL, and agricultural) (mineralization rate: 2.47 ± 1.74 mg N·kg−1·d−1; nitrification rate: 1.43 ± 1.30 mg N·kg−1·d−1). Backward stepwise regression analysis of the results indicated salinity to be the most important factor controlling nitrogen transformation rates. It is likely that soils undergoing frequent seawater exposure or excessive evaporation may experience slowdown in nitrogen cycling due to salinization leading to reduced nutrient production and consumption. Due to climate change, the areal extent of coastal drylands undergoing such decline in nutrient production is likely to increase, eventually leading to loss of productivity and desertification.

Abstract The 2015 eruption at Axial Seamount, an active volcano at a depth of 1500 m in the Northeast Pacific, marked the first time a seafloor eruption was detected and monitored by an in situ cabled observatory—the Cabled Array, which is part of the Ocean Observatories Initiative. After the onset of the eruption, eight cabled and noncabled instruments on the seafloor recorded unusual, nearly synchronous and spatially uniform temperature increases of 0.6–0.7°C across the southern half of the caldera and neighboring areas. These temperature signals were substantially different from those observed after the 2011 and 1998 eruptions at Axial and hence cannot be explained by emplacement of the 2015 lava flows on the seafloor. In this study, we investigate several possible explanations for the 2015 temperature anomalies and use a numerical model to test our preferred hypothesis that the temperature increases were caused by the release of a warm, dense brine that had previously been stored in the crust. If our interpretation is correct, this is the first time that the release of a hydrothermal brine has been observed due to a submarine eruption. This observation would have important implications for the salt balance of hydrothermal systems and the fate of brines stored in the subsurface. The observation of the 2015 temperature anomalies and the modeling presented in this study also demonstrate the importance of contemporaneous water column observations to better understand hydrothermal impacts of submarine eruptions.