The monsoon freshwater and wind forcing drive high Sea Surface Salinity (SSS) contrasts and variability (up to 10 pss range) in the Bay of Bengal (BoB), with important consequences for upper ocean ...mixing and air-sea interactions. Synoptic SSS maps did only become available with the advent of L-band radiometers in 2010, due to insufficient prior in situ data coverage. Here, we build tools aiming at reconstructing the monthly BoB SSS at ¼° resolution since 2002 from AMSR-E radiometer data. The C-band low sensitivity to SSS requires a very careful processing. Taking the X- minus C- bands signals reduce the impact of Sea Surface Temperature (SST) and wind on brightness temperatures. It was however further necessary to train the algorithm with SSS data from L-Band radiometers to remove residual surface winds, SST, and atmospheric water contents signals. We also found that a separate treatment of the ascending and descending passes was necessary, as well as a proper data screening to minimize contamination by land signals. The resulting SSS product reproduces the broad BoB climato-logical SSS, and has a 0.66 correlation, 1.08 pss rms-difference to co-located in situ surface salinity from Array for Real-time Geostrophic Oceanography (ARGO) floats. Comparisons with ocean re-analyses in two SSS interannual variability hotspots indicate poor performance in the Northern BoB, but some skill along the East coast of India. Our results provide a proof of concept for reconstructing the BoB SSS from AMSR-E data, and we discuss possible future improvements of the data processing to further reduce the impact of spurious signals.
Thirty crop species provide 90% of our food, most of which display severe yield losses under moderate salinity. Securing and augmenting agricultural yield in times of global warming and population ...increase is urgent and should, aside from ameliorating saline soils, include attempts to increase crop plant salt tolerance. This short review provides an overview of the processes that limit growth and yield in saline conditions. Yield is reduced if soil salinity surpasses crop‐specific thresholds, with cotton, barley and sugar beet being highly tolerant, while sweet potato, wheat and maize display high sensitivity. Apart from Na+, also Cl−, Mg2+, SO42‐ or HCO3‐ contribute to salt toxicity. The inhibition of biochemical or physiological processes cause imbalance in metabolism and cell signalling and enhance the production of reactive oxygen species interfering with cell redox and energy state. Plant development and root patterning is disturbed, and this response depends on redox and reactive oxygen species signalling, calcium and plant hormones. The interlink of the physiological understanding of tolerance processes from molecular processes as well as the agronomical techniques for stabilizing growth and yield and their interlinks might help improving our crops for future demand and will provide improvement for cultivating crops in saline environment.
Background
Soil salinization has a major impact on crop production and it is expected to increase in area in the coming years. In this scenario, exploring the potential of halophytes and their ...plant-associated microbiomes as to increase phytoremediation strategies represents a suitable and sustainable strategy.
Methods
We conducted a microcosm experiment with the halophyte
Atriplex nummularia
, cultivating it in two contrasting soils (clay and sandy) at distinct levels of salinity (0, 10 and 20 mS/cm). After 109 days, we assessed its growth and bacteriome composition, through 16S rRNA gene sequencing of the leaf and root endospheres, as well as rhizosphere.
Results
A
.
nummularia
showed increased growth under salinity levels of up to 20 mS/cm in both soils. Salinity and soil type had an effect in determining the rhizosphere bacterial communities of
A
.
nummularia
, with a stronger signal in the sandy soil. Most interestingly, no differences were found in endophytic bacterial communities, suggesting a strong buffering effect of the plant physiology, even though this halophyte accumulates NaCl. Last, functional prediction based on a subset of differentially abundant taxa in the rhizosphere revealed an increase in plant-growth promotion and salinity tolerance traits in higher salinity, indicating simultaneous selection by salinity and
A
.
nummularia
under stress.
Conclusion
Collectively, these results provide valuable insights into halophyte-associated bacteria, advancing our understanding of this complex system with potential application in phytoremediation strategies for saline soils.
•Annual cycle of tropical salinity minima leads subtropical maxima by six months.•The six-month phase shift is set by Ekman poleward transport of tropical salinities.•Rainfall of the Double ...Intertropical Convergence Zones shapes tropical low salinities.•Poleward Ekman transport synchronizes tropical low and subtropical high salinities.•Recent North Pacific freshening reflects poleward spreading of ENSO influence.
Recent satellite observations reveal that the annual cycles of tropical sea surface salinity (SSS) minimum (Smin) and subtropical SSS maximum (Smax) are phased locked, with the former leading the latter by six months. The evidence suggests an interconnected nature between the salinity extrema, motivating an investigation into the underlying mechanisms. It is found that the poleward Ekman transport, driven by trade winds, stands as a pivotal conduit linking the influence of tropical freshwater to high salinities in the subtropical oceans. Two key aspects are central to the operation of this advective oceanic pathway. One is the annual formation of the near-equatorial Smin zones by Ekman convergence of the freshwater sourced from the double Intertropical Convergence Zones. The other is the advection time taken by Ekman transport traveling at an average speed of approximately 7 cm s−1. This speed allows the near-equatorial salinity anomalies to be carried to the subtropical Smax fringes in six months, aligning closely with the observed semi-annual phase shift between Smin and Smax. During El Niño - Southern Oscillation (ENSO) warm and cold episodes in recent decade, poleward propagation of near-equatorial low salinity anomalies was particularly prominent, leading to substantial surface freshening in the subtropical Pacific. Interestingly, the latitudinal spread of the ENSO-triggered SSS anomalies is confined within the domain of the poleward Ekman transport. This confinement reaffirms the inherent connection between the tropical Smin and subtropical Smax regions, shedding light on the intricate interplay between oceanic processes, the water cycle, and SSS distributions.
Root microbiota is a crucial determinant of plant productivity and stress tolerance. Here, we hypothesize that the superior halo-tolerance of seepweed Suaeda salsa is tightly linked to a specialized ...belowground microbiome. To test this hypothesis, we performed a phylogenetic trait-based framework analysis based on bacterial 16S rRNA gene and fungal nuclear rRNA internal transcribed spacer profiling. Data showed that the dominant α-proteobacteria and γ-proteobacteria communities in bulk soil and root endosphere tend to be phylogenetically clustered and at the same time exhibit phylogenetic over-dispersion in rhizosphere. Likewise, the dominant fungal genera occurred at high phylogenetic redundancy. Interestingly, we found the genomes of rhizospheric and endophytic bacteria associated with S. salsa to be enriched in genes contributing to salt stress acclimatization, nutrient solubilization and competitive root colonization. A wide diversity of rhizobacteria with similarity to known halotolerant taxa further supported this interpretation. These findings suggest that an ecological patterned root-microbial interaction strategy has been adopted in S. salsa system to confront soil salinity. We also demonstrated that the potential core microbiome members improve non-host plants growth and salt tolerance. This work provides a platform to improve plant fitness with halophytes-microbial associates and novel insights into the functions of plant microbiome under salinity.
The Soil Moisture and Ocean Salinity (SMOS) satellite mission, operational since 2010, relies on an L-band microwave interferometric radiometer to generate brightness temperature (BT) images along ...the swath, with global coverage every three days. These images are then used to derive sea surface salinity (SSS) with an effective resolution of less than 50 km. However, signal acquisition in some ocean regions is intermittently and significantly disrupted by radio frequency interferences (RFIs) from various terrestrial military or civilian sources worldwide. We develop a new methodology based on principal component and regression analyses to extract the RFI signatures in time and space, thereby enabling the construction of a corrected SSS estimate along the swath. This method successfully filters out many disruptive features characterized by long and wide branches occurring around the RFI sources, hence recovering SSS variability as demonstrated in comparison to in situ reference data. This correction methodology is an alternative to separate filtering procedures that were applied on BT at Level 1. Independent information indicating the probability of RFI occurrence on land areas or nearby is used to verify the timing of oceanic RFI contamination inferred by the correction process. The methodology performs particularly well in areas where the probability is close to 1 for a significant and contiguous portion of the entire period. Already applied with significant improvement in three selected regions, this exemplary study is a starting point for expanding and systematizing the methodology to treat as many RFI-polluted regions as possible and to recover SMOS SSS variability.
The influence of NO.sub.3.sup.--N on growth and osmotic adjustment was studied in Tamarix laxa Willd., a halophyte with salt glands on its twigs. Seedlings of T. laxa Willd. were exposed to 1 mM ...(control) or 300 mM NaCl, with 0.05, 1 or 10 mM NO.sub.3.sup.--N for 24 days. The relative growth rate of seedlings at 300 mM NaCl was lower than that of control plants at all NO.sub.3.sup.--N levels, but the concentrations of organic N and total N in the twigs did not differ between the two NaCl treatments. Increasing NO.sub.3.sup.- supply under 300 mM NaCl improved the growth of T. laxa, indicating that NO.sub.3.sup.- played positive roles in improving salt resistance of the plant. The twigs of T. laxa Willd. accumulated mainly inorganic ions, especially Na.sup.+ and Cl.sup.-, to lower osmotic potential (ψs): the contributions of Na.sup.+ and Cl.sup.- to ψs were estimated at 31% and 27% respectively, at the highest levels of supply of both NaCl and NO.sub.3.sup.--N. The estimated contribution of NO.sub.3.sup.--N to ψs was as high as 20% in the twigs in these conditions, indicating that NO.sub.3.sup.- was also involved in osmotic adjustment in the twigs. Furthermore, increases in tissue NO.sub.3.sup.- were accompanied by decreases in tissue Cl.sup.- and proline under 300 mM NaCl. The estimated contribution of proline to ψs declined as with NO.sub.3.sup.--N supply increased from 1 to 10 mM, while the contributions of nitrate to ψs were enhanced under 300 mM NaCl. This suggested that higher accumulation of nitrate in the vacuole alleviated the effects of salinity stress on the plant by balancing the osmotic potential. In conclusion, NO.sub.3.sup.--N played both nutritional and osmotic roles in T. laxa Willd. in saline conditions. Keywords Tamarix laxa willd * Salt stress * NO.sub.3.sup.--N . Osmoregulation * Proline
Dimethylsulphoniopropionate (DMSP) is one of the most abundant and widespread organic sulfur molecules in the marine environment and has substantial physiological and ecological importance, from ...subcellular to global scales. Despite its diverse range of implications in the environment, little understanding of the physiological role of DMSP in the cell exists. Here, we report the physiological response of a non-DMSP-producing diatom Thalassiosira weissflogii grown at different salinities (15, 35 and 55 ppt) in the presence and absence of DMSP. Hypersaline conditions (55 ppt) negatively affected growth rate and hyposaline conditions (15 ppt) caused an increase in cell volume, yet no effect was observed on the photophysiological state of the algae, demonstrating a broad salinity tolerance in T. weissflogii. Addition of DMSP and subsequent uptake by T. weissflogii had no effect on the salinity-induced symptoms. Importantly, using a non-DMSP-producing diatom, we observed some of the first direct evidence of the intracellular role of DMSP as an antioxidant through the quenching of damaging reactive oxygen species (ROS), which based on its pattern, was likely due to the growth phase of the culture. This study confirms the utility of T. weissflogii as a model organism for DMSP-related physiological studies, with results revealing that DMSP accumulation reduces growth-related reactive oxygen in T. weissflogii.
Barystatic sea level rise (SLR) caused by the addition of freshwater to the ocean from melting ice can in principle be recorded by a reduction in seawater salinity, but detection of this signal has ...been hindered by sparse data coverage and the small trends compared to natural variability. Here, we develop an autoregressive machine learning method to estimate salinity changes in the global ocean from 2001 to 2019 that reduces uncertainties in ocean freshening trends by a factor of four compared to previous estimates. We find that the ocean mass rose by 13,000 ± 3,000 Gt from 2001 to 2019, implying a barystatic SLR of 2.0 ± 0.5 mm/yr. Combined with SLR of 1.3 ± 0.1 mm/yr due to ocean thermal expansion, these results suggest that global mean sea level rose by 3.4 ± 0.6 mm/yr from 2001 to 2019. These results provide an important validation of remote‐sensing measurements of ocean mass changes, global SLR, and global ice budgets.
Plain Language Summary
Global sea level rise (SLR) is caused by heating of the ocean, and by the input of freshwater from the melting of glaciers and ice caps. Global freshwater input to the oceans from melting ice during the 21st century has primarily been tracked by satellites that measure changes in the mass of the ocean. Here, we show that trends in global SLR can also be accurately tracked by global observations of ocean salinity changes, as freshwater runoff from melting ice enters the ocean and dilutes ocean salinity. These results show that ocean salinity measurements are critical for monitoring global sea level changes, particularly as polar warming intensifies and the melting of ice sheets accelerates.
Key Points
A new full‐depth ocean salinity product yields robust global freshening trend of (35 ± 10) × 10−6 yr−1 from 2001 to 2019
Combined with estimates of sea ice loss, this freshening implies that ocean mass rose by 13,000 ± 3,000 Gt from 2001 to 2019
Sea level rise derived from ocean temperature and salinity measurements is 3.4 ± 0.6 mm/yr, confirming the satellite altimetry trend
Abstract Multidecadal variability of the Indonesian Throughflow (ITF) is crucial for the Indo-Pacific and global climate due to significant interbasin exchanges of heat and freshwater. Previous ...studies suggest that both wind and buoyancy forcing may drive ITF variability, but the role of precipitation and salinity effect in the variability of ITF on multidecadal time scales remains largely unexplored. Here, we investigate the multidecadal changes and long-term trend of the ITF transport during the past six decades, with a focus on the role of precipitation and salinity effect. The diverse datasets consistently indicate a substantial upward trend in the halosteric component of geostrophic transport of ITF in the outflow region at 114°E during the six decades. We find that the meridional differences of the salinity trend in the outflow region explain the increasing trend of the halosteric component of ITF transport. On a larger scale, the tropical western Pacific Ocean and Indonesian seas have experienced significant freshening, which has strengthened the Indo-Pacific pressure gradient and thus enhanced the ITF. In contrast, the equatorial trade wind in the western Pacific Ocean has weakened over recent decades, implying that changes in wind forcing have contributed to weakening the ITF. The combined effect of strengthened halosteric and weakened thermosteric components has resulted in a weak strengthening for the total ITF with large uncertainties. Although both the thermosteric and halosteric components are associated with natural climate modes, our results suggest that the importance of salinity effect is likely increasing given the enhanced water cycle under global warming.
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