Salinity modifies heavy metals and arsenic absorption by the halophyte plant species Kosteletzkya pentacarpos and pollutant leaching from a polycontaminated substrate

Sub-lethal effects of metal(loid) contamination on the halophyte Sarcocornia quinqueflora with links to plant photosynthetic performance and biomass - A field study

Two saltmarsh locations within Lake Macquarie, NSW, Australia were selected to investigate the uptake and partitioning of metal(loid)s Cu, Zn, As, Se, Cd and Pb in the Australian saltmarsh halophyte, Sarcocornia quinqueflora and the associated sub-lethal effects of metal(loid)s on plant health, including photosynthetic performance, biomass, and productivity. Metal(loid)s primarily accumulated to roots (BCF > 1). Barriers to transport were observed at the root to non-photosynthetic stem transition (TF < 1) for all metal(loid)s, suggesting this species is suitable for phytostabilisation. Sediment and plant tissue metal(loid) concentrations were significantly correlated with photosynthetic performance and plant biomass. As such, the action of sediment and tissue metal(loid)s on photosynthetic performance and the subsequent effect on biomass of S.quinqueflora appear to be suitable targets for molecular analyses to further elucidate mechanisms responsible for the observed adverse effects and the development of adverse outcome pathways.

Evaluating phytoremediation potential and nutrients status of Bassia indica (Wight) A. J. Scott (Indian Bassia) in a cadmium-contaminated saline soil

Bassia indica (Wight) A. J. Scott is a fast-growing halophyte suitable for the remediation of saline lands on a large scale. However, no information is available regarding its phytoremediation potential for cadmium (Cd) alone or in combination with salinity. Besides evaluating phytoremediation, assessing micronutrient hemostasis as a crucial physiological insight into the mechanism involved in the tolerance of B. indica under saline soil contaminated with Cd was subjected. Under salinity stress, a considerable amount of sodium accumulates in the plant. Moreover, the accumulation of sodium increased by Cd stress levels. The increase in the exchangeable form of Cd in the rhizosphere in the presence of NaCl ions further elevated the Cd content in the plant tissues. For instance, compared to non-saline conditions, applying 2.5 and 5 g NaCl kg-1 to soil treated with 60 mg Cd kg-1 increased exchangeable Cd by 28.4 and 49.5% in rhizosphere soil, which led to increased cadmium content by 16.1 and 29.6% in the root (as a main part of Cd accumulation), respectively. Under most stress conditions, potassium homeostasis in the shoot remained undisturbed. It was observed that this plant could transfer an optimal level of potassium from the roots to the shoots at a moderate salinity level. Changes and the distribution of Cu and Zn levels followed a similar pattern in the plant, indicating a common regulation mechanism for these nutrients. Generally, the plant could maintain an appropriate level of Fe, Zn, and Cu ions under most stressed conditions. However, the level of Mn decreased significantly under severe stress levels. Growth parameters, tolerance index, and the values of translocation factor < 1 and shoot bioconcentration factor > 1 under 5 mg Cd kg-1 soil treatment at different salinity levels indicated that B. indica could mitigate the detrimental effect of Cd toxicity and tolerate the NaCl stress via a phytostabilizer mechanism. However, the shoot bioconcentration factor values were very close to one at other Cd levels. Therefore, considering the obtained evidence and the innate ability of B. indica to remediation salinity, this plant is still recommended, even for higher Cd levels (even until 30 mg kg-1), in the presence of salinity.

Unraveling the interplay between environmental microplastics and salinity stress on Mytilus galloprovincialis larval development: A holistic exploration

The rise of plastic production has triggered a surge in plastic waste, overwhelming marine ecosystems with microplastics. The effects of climate change, notably changing salinity, have shaped the dynamics of coastal lagoons. Thus, understanding the combined impact of these phenomena on marine organisms becomes increasingly crucial. To address these knowledge gaps, we investigated for the first time the interactive effects of environmental microplastics (EMPs) and increased salinity on the early development of Mytilus galloprovincialis larvae. Morphological assessments using the larval embryotoxicity test revealed larval anomalies and developmental arrests induced by EMPs and increased salinity. Transcriptomic analyses targeting 12 genes involved in oxidative stress, apoptosis, DNA repair, shell formation, and stress proteins were conducted on D-larvae uncovered the potential effects of EMPs on shell biomineralization, highlighting the role of Histidine Rich Glycoproteine (HRG) and tubulin as crucial adaptive mechanisms in Mytilus sp. in response to environmental shifts. Furthermore, we explored oxidative stress and neurotoxicity using biochemical assays. Our findings revealed a potential interaction between EMPs and increased salinity, impacting multiple physiological processes in mussel larvae. Our data contribute to understanding the cumulative effects of emerging anthropogenic pollutants and environmental stressors, emphasizing the need for a holistic approach to assessing their impact on marine ecosystems.

Uptake and distribution of metal(loid)s in two rare species of saltmarsh, blackseed samphire, Tecticornia pergranulata, and narrow-leafed wilsonia, Wilsonia backhousei, in New South Wales, Australia

The uptake and distribution of copper, zinc, arsenic, and lead was examined in two rare Australian saltmarsh species, Tecticornia pergranulata and Wilsonia backhousei. The bioconcentration factors and translocation factors were generally much lower than one, except for the Zn translocation factors for T. pergranulata. When compared to other Australian saltmarsh taxa, these species generally accumulated the lowest levels observed among taxa, especially in terms of their BCFs. Essential metals tended to be regulated, while non-essential metals increased in concentration with dose during transport among compartments, a pattern not previously observed in Australian saltmarsh taxa. The uptake of metals into roots was mainly explained by total sediment metal loads as well as more acidic pH, increased soil organic matter, and decreased salinity. The low uptake and limited translocation observed in these rare taxa may offer a competitive advantage for their establishment and survival in the last urbanised populations, where legacy metal contamination acts as a selective pressure.

Quantitative relationship between soil pH and electrical conductivity values and cadmium phytoavailability for Chinese cabbage under simulated conditions

Pot experiments were conducted to investigate the impacts of continuous addition of different concentrations of calcium chloride (CaCl2) and/or low-molecular-weight organic acids (LMWOAs) on soil pH, electrical conductivity (EC), and cadmium (Cd) transformation. These factors subsequently affected Cd phytoavailability in a system consisting of Cd-contaminated soil and Chinese cabbage (Brassica chinensis L.). The results indicate that CaCl2 addition had a greater impact on reducing soil pH value, increasing soil EC value, and enhancing Cd phytoaccumulation in Chinese cabbage compared to LMWOAs. When soil pH dropped by 0.3 unit and the soil EC increased by 500 µS cm-1, the Cd concentration in the Chinese cabbage shoots was 3 times higher than that in the control group. Throughout two planting terms of Chinese cabbage, the addition of CaCl2 (1.6-3.2 g kg-1) and LMWOAs (≤ 1.0 g kg-1) led to phytoextracted Cd concentration exceeding exchangeable Cd concentration in soil samples before the pot experiment. Regarding phytoextracted Cd, desorption from carbonate-bound Cd contributes more than desorption from bound to organic matter Cd and adsorption to Fe/Mn oxide Cd. This study underscores the influence of soil pH and EC value variations and Cd transformation on Cd phytoavailability. Special attention should be given to leafy vegetables grown in Cd-contaminated soil, as the phytoavailable Cd concentration reaches approximately 2.0 µg kg-1, which may lead to Cd levels surpassing acceptable limits for Chinese cabbage.

Bioaccumulation and speciation of arsenic in plankton from tropical soda lakes along a salinity gradient

Uptake and transformation of arsenic (As) by living organisms can alter its distribution and biogeochemical cycles in the environment. Although well known for its toxicity, several aspects of As accumulation and biological transformation by field species are still little explored. In this study, the bioaccumulation and speciation of As in phytoplankton and zooplankton from five soda lakes in the Brazilian Pantanal wetland were studied. Such lakes exhibited contrasting biogeochemical characteristics along an environmental gradient. Additionally, the influence of contrasting climatic events was assessed by collecting samples during an exceptional drought in 2017 and a flood in 2018. Total As (AsTot) content and speciation were determined using spectrometric techniques, while a suspect screening of organoarsenicals in plankton samples was carried out by high-resolution mass spectrometry. Results showed that AsTot content ranged from 16.9 to 62.0 mg kg-1 during the dry period and from 2.4 to 12.3 mg kg-1 during the wet period. The bioconcentration and bioaccumulation factors (BCF and BAF) in phytoplankton and zooplankton were found to be highly dependent on the lake typology, which is influenced by an ongoing evapoconcentration process in the region. Eutrophic and As-enriched lakes exhibited the lowest BCF and BAF values, possibly due to the formation of non-labile As complexes with organic matter or limited uptake of As by plankton caused by high salinity stress. The season played a decisive role in the results, as significantly higher BCF and BAF values were observed during the flooding event when the concentration of dissolved As in water was low. The diversity of As species was found to be dependent on the lake typology and on the resident biological community, cyanobacteria being responsible for a significant portion of As metabolism. Arsenosugars and their degradation products were detected in both phytoplankton and zooplankton, providing evidence for previously reported detoxification pathways. Although no biomagnification pattern was observed, the diet seemed to be an important exposure pathway for zooplankton.

Signaling and crosstalk of rhizobacterial and plant hormones that mediate abiotic stress tolerance in plants

Agricultural areas exhibiting numerous abiotic stressors, such as elevated water stress, temperatures, and salinity, have grown as a result of climate change. As such, abiotic stresses are some of the most pressing issues in contemporary agricultural production. Understanding plant responses to abiotic stressors is important for global food security, climate change adaptation, and improving crop resilience for sustainable agriculture, Over the decades, explorations have been made concerning plant tolerance to these environmental stresses. Plant growth-promoting rhizobacteria (PGPR) and their phytohormones are some of the players involved in developing resistance to abiotic stress in plants. Several studies have investigated the part of phytohormones in the ability of plants to withstand and adapt to non-living environmental factors, but very few have focused on rhizobacterial hormonal signaling and crosstalk that mediate abiotic stress tolerance in plants. The main objective of this review is to evaluate the functions of PGPR phytohormones in plant abiotic stress tolerance and outline the current research on rhizobacterial hormonal communication and crosstalk that govern plant abiotic stress responses. The review also includes the gene networks and regulation under diverse abiotic stressors. The review is important for understanding plant responses to abiotic stresses using PGPR phytohormones and hormonal signaling. It is envisaged that PGPR offer a useful approach to increasing plant tolerance to various abiotic stresses. However, further studies can reveal the unclear patterns of hormonal interactions between plants and rhizobacteria that mediate abiotic stress tolerance.

Salinity elevates Cd bioaccumulation of sea rice cultured under co-exposure of cadmium and salt

Salt-tolerant rice (sea rice) is a key cultivar for increasing rice yields in salinity soil. The co-existence of salinity and cadmium (Cd) toxicities in the plant-soil system has become a great challenge for sustainable agriculture, especially in some estuaries and coastal areas. However, little information is available on the Cd accumulating features of sea rice under the co-stress of Cd and salinity. In this work, a hydroponic experiment with combined Cd (0, 0.2, 0.8 mg/L Cd²⁺) and saline (0, 0.6%, and 1.2% NaCl, W/V) levels and a pot experiment were set to evaluate the Cd toxic risks of sea rice. The hydroponic results showed that more Cd accumulated in sea rice than that in the reported high-Cd-accumulating rice, Chang Xianggu. It indicated an interesting synergistic effect between Cd and Na levels in sea rice, and the Cd level rose significantly with a concomitant increase in Na level in both shoot (r = 0.54, p < 0.01) and root (r = 0.66, p < 0.01) of sea rice. Lower MDA content was found in sea rice, implying that the salt addition probably triggered the defensive ability against oxidative stress. The pot experiment indicated that the coexistent Cd and salinity stress further inhibited the rice growth and rice yield, and the Cd concentration in rice grain was below 0.2 mg/kg. Collectively, this work provides a general understanding of the co-stress of Cd and salinity on the growth and Cd accumulation of sea rice. Additional work is required to precisely identify the phytoremediation potential of sea rice in Cd-polluted saline soil.

Salinity and temperature influence removal levels of heavy metals and chloride from water by wetland plants

Stormwater with low temperatures and elevated salinity, common in areas where deicing salt is used, might affect the removal of heavy metals by plants in stormwater treatment systems such as floating treatment wetlands. This short-term study evaluated the effects of combinations of temperature (5, 15, and 25 °C) and salinity (0, 100, and 1000 mg NaCl L^-1) on the removal of Cd, Cu, Pb, and Zn (1.2, 68.5, 78.4, and 559 μg L^-1) and Cl^- (0, 60, and 600 mg Cl^- L^-1) by Carex pseudocyperus, C. riparia, and Phalaris arundinacea. These species had previously been identified as suitable candidates for floating treatment wetland applications. The study found high removal capacity in all treatment combinations, especially for Pb and Cu. However, low temperatures decreased the removal of all heavy metals, and increased salinity decreased the removal of Cd and Pb but had no effect on the removal of Zn or Cu. No interactions were found between the effects of salinity and of temperature. Carex pseudocyperus best removed Cu and Pb, whereas P. arundinacea best removed Cd, Zu, and Cl^-. The removal efficacy for metals was generally high, with elevated salinity and low temperatures having small impacts. The findings indicate that efficient heavy metal removal can also be expected in cold saline waters if the right plant species are used.

River water influenced by shale gas wastewater discharge for paddy irrigation has limited effects on soil properties and microbial communities

The processes of hydraulic fracturing to extract shale gas generate a large amount of wastewater, and the potential impacts of wastewater discharge after treatment are concerning. In this field study, we investigated the effects of the irrigation of paddy fields for 2 consecutive years by river water that has been influenced by shale gas wastewater discharge on soil physicochemical properties, microbial community structure and function, and rice grain quality. The results showed that conductivity, chloride and sulfate ions in paddy soils downstream of the outfall showed an accumulative trend after two years of irrigation, but these changes occurred on a small scale (<500 m). Two-year irrigation did not cause the accumulation of trace metals (barium, cadmium, chromium, copper, lead, strontium, zinc, nickel, and uranium) in soil and rice grains. Among all soil parameters, the accumulation of chloride ions was the most pronounced, with concentrations in the paddy soil at the discharge site 13.3 times higher than at the upstream control site. The use of influenced river water for paddy irrigation positively increased the soil microbial diversity, but these changes occurred after two years of irrigation and did not occur after one year of irrigation. Overall, the use of river water affected by shale gas wastewater discharge for agricultural irrigation has limited effects on agroecosystems over a short period. Nevertheless, the possible negative effects of contaminant accumulation in soil and rice caused by longer-term irrigation should be seriously considered.

Impact of organic amendments on the bioavailability of heavy metals in mudflat soil and their uptake by maize

Organic amendments (OAs) can be a sustainable and effective method for mudflat soil improvement. A field experiment was conducted to investigate the potential of OA application to mudflat soil improvement. We measured the pH, soil organic matter (SOM), salinity, maize growth, and heavy metal (HM) accumulation in OA-applied soils, and maize tissues after three OAs, sewage sludge (SS), Chinese medical residue (CMR), and cattle manure (CM), were applied at the application rates of 0, 30, 75, 150, and 300 t ha^-1. OA application significantly increased the SOM and decreased the pH and salinity of mudflat soils. The maize biomass and HM contents in soil and maize increased after OA application. The bioavailability and bioconcentration of HMs were generally in the sequence of SS > CMR > CM. The average bioavailability ratios of HMs were in the order of Cd > Zn > Cu > Mn > Ni. The bioconcentration of Zn and Cd by maize was highest, followed by Mn, Cu, and Ni. SOM, pH, and salinity were the important factors regulating soil available HMs and, subsequently, HM accumulation in maize. Among the three OAs, SS is most effective in decreasing soil salinity, and increasing the SOM, bioavailability, and bioconcentration of HMs. On the other hand, CM was the best OA because it promoted significant maize growth yet maintained low HM contamination risk.

Influence of Soil Salinity on Selected Element Contents in Different Brassica Species

Climate changes in coastal regions cause increased soil salinity, a well-known type of environmental stress for a high number of agricultural crop species, including Brassicaceae, whose growth and development, and consequently the crop quality and yield, are affected by salinity stress. The aim of the present study is to investigate the effect of salt stress on micro- and macro-element homeostasis in different Brassica crops. Kale (Brassica oleracea var. acephala), white cabbage (B. oleracea var. capitata) and Chinese cabbage (B. rapa ssp. pekinensis) were grown hydroponically and treated with 200 mmol/L sodium chloride for 24 h to mimic short-term salt stress. The contents of Al, Ca, K, Mg, Na, B, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V and Zn were determined in the roots and leaves of the salt-treated plants and corresponding controls by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. While Al, Ca, K, Mg and Na were determined in the mg/g range, the contents of the other elements were found at the µg/g level. A statistical analysis of the obtained data showed that the applied salt treatment significantly influenced the single-element contents in different plant parts. The major elements Ca, K and Mg were mainly unaffected in the more-salt-tolerant kale and white cabbage under salinity stress, while K and Mg were significantly decreased in the more-sensitive Chinese cabbage. The levels of micro-elements were found to be species/variety specific. In general, potentially toxic elements were accumulated in the roots of salt-treated plants to a higher extent than in the corresponding controls.

Water and soil contaminated by arsenic: the use of microorganisms and plants in bioremediation

Owing to their roles in the arsenic (As) biogeochemical cycle, microorganisms and plants offer significant potential for developing innovative biotechnological applications able to remediate As pollutions. This possible use in bioremediation processes and phytomanagement is based on their ability to catalyse various biotransformation reactions leading to, e.g. the precipitation, dissolution, and sequestration of As, stabilisation in the root zone and shoot As removal. On the one hand, genomic studies of microorganisms and their communities are useful in understanding their metabolic activities and their interaction with As. On the other hand, our knowledge of molecular mechanisms and fate of As in plants has been improved by laboratory and field experiments. Such studies pave new avenues for developing environmentally friendly bioprocessing options targeting As, which worldwide represents a major risk to many ecosystems and human health.

Kosteletzkya pentacarpos: A Potential Halophyte Candidate for Phytoremediation in the Meta(loid)s Polluted Saline Soils

Kosteletzkya pentacarpos (L.) Ledebour is a perennial facultative halophyte species from the Malvacea family that grows in coastal areas with high amounts of salt. The tolerance of K. pentacarpos to the high concentration of salt (0.5–1.5% salinity range of coastal saline land) has been widely studied for decades. Nowadays, with the dramatic development of the economy and urbanization, in addition to the salt, the accumulation of mate(loid)s in coastal soil is increasing, which is threatening the survival of halophyte species as well as the balance of wetland ecosystems. Recently, the capacity of K. pentacarpos to cope with either single heavy metal stress or a combination of multiple meta(loid) toxicities was studied. Hence, this review focused on summarizing the physiological and biochemical behaviors of K. pentacarpos that has been simultaneously exposed to the combination of several meta(loid) toxicities. How the salt accumulated by K. pentacarpos impacts the response to meta(loid) stress was discussed. We conclude that as a potential candidate for phytoremediation, K. pentacarpos was able to cope with various environmental constrains such as multiple meta(loid) stresses due to its relative tolerance to meta(loid) toxicity.

Spatio-temporal dynamics of arbuscular mycorrhizal fungi and soil organic carbon in coastal saline soil of China

A comprehensive understanding of the relationship between arbuscular mycorrhizal (AM) fungi and coastal saline soil organic carbon (SOC) is crucial for analysis of the function of coastal wetlands in soil carbon sequestration. In a field experiment, the temporal and spatial dynamics of AM fungi, glomalin-related soil protein (GRSP) – which is described as a N-linked glycoprotein and the putative gene product of AM fungi, SOC, and soil aggregates were investigated in halophyte Kosteletzkya virginica rhizosphere soil of coastal saline areas of North Jiangsu, China. Soil samples were collected from a depth of up to 30 cm in two plantation regions from August 2012 to May 2013. Results showed K. virginica formed a strong symbiotic relationship to AM fungi. AM colonization and spore density were the highest in the 10–20 cm soil layer of Jinhai farm in August 2012, because of the presence of numerous fibrous roots in this soil layer. The total GRSP and SOC were the highest in the 0–10 cm soil layer in May 2013 and November 2012, respectively. Correlation coefficient analysis revealed that AM colonization and spore density were positively correlated with total GRSP. Meanwhile, total GRSP was significantly positively correlated with large macroaggregates (>3 mm), SOC, total P, Olsen P, and soil microbial biomass carbon (SMBC), but negatively correlated with microaggregates (<0.25 mm), soil EC, total N, and pH. SOC was positively correlated with spore density, large macroaggregates, small macroaggregates (2–0.25 mm), alkaline N, and SMBC and negatively correlated with microaggregates, EC, pH, and total K. Although it may be a statistical artifact, we found an interesting phenomenon that there was no significant correlation between soil aggregates and AM colonization or spore density. Hence, total GRSP is a vital source of saline soil C pool and an important biological indicator for evaluating coastal saline SOC pool and soil fertility, while AM colonization or spore density may not be.