Silicon supplementation enhances productivity, water use efficiency and salinity tolerance in maize.

Drought and salinity stress severely inhibits the growth and productivity of crop plants by limiting their physiological processes. Silicon (Si) supplementation is considerd as one of the promising approaches to alleviate abiotic stresses such as drought and salinity. In the present study, a field experiment was conducted over two successive growth seasons (2019-20) to investigate the effect of foliar application of Si at two concentrations (1 and 2 kg Si ha-1) on the growth, yield and physiological parameters of three maize cultivars (ES81, ES83, and ES90) under three levels of irrigation salinity) [1000 (WS1), 2000 (WS2) and 3000 (WS3) mg L-1NaCl]. In this study, A trickle irrigation system was used. Si application significantly mitigated the harsh effects of salinity on growth and yield components of maize, which increased at all concentrations of Si. In irrigation with S3 salinity treatment, grain yield was decreased by 32.53%, however, this reduction was alleviated (36.19%) with the exogenous foliar application of Si at 2 kg Si ha-1. At salinity levels, Si application significantly increased maize grain yield (t ha-1) to its maximum level under WS of 1000 mg L-1, and its minimum level (Add value) under WS of 3000 mg L-1. Accordingly, the highest grain yield increased under Si application of 2 kg Si ha-1, regardless of salinity level and the cultivar ES81 achieved the highest level of tolerance against water salinity treatments. In conclusion, Application of Si at 2 kg Si ha-1 as foliar treatment worked best as a supplement for alleviating the adverse impacts of irrigation water salinity on the growth, physiological and yield parameters of maize.

Assessing the risk of toxic metals contamination and phytoremediation potential of mangrove in three coastal sites along the Red Sea.

Assessing toxic metals (TMs) contamination and phytoremediation potentiality in coastal mangrove lagoons is needed for applying sustainable management of this ecosystem. Consequently, here we determined the pseudo-total content of TMs in the sediments and mangrove plants (leaves, stems, aerial roots, and fine roots) collected from Al-Shuaiba, Yanbu, and Jeddah lagoons, along the coast of Red Sea. The contamination degree was assessed using different indices and the potentiality of mangroves for TMs phytoremediation was determined. The average total metals content (mg kg-1) in the sediments ranged from 1806 to 9580 for Fe, 65 to 195 for Mn, 3.9 to 25.9 for Cu, 5.5 to 16.4 for Zn, 0.09 to 0.42 for Cd, 8.9 to 20.9 for Cr, 32.8 to 37.9 for Ni, and from 0.69 to 6.7 for Pb. The sediments of Yanbu site contained the highest content of all metals (except for Cu), while Al-Shuaiba sediments contained the lowest values. The contamination factor (CF) showed that the sediments of Yanbu and Jeddah suffer from high and moderate contamination degree of Cd. These sites suffer from moderate grade of Ni contamination. The CF values of Fe, Mn, Cr, Cu, and Zn in the three sites were lower than unity, which show low contamination degree. Iron, Cr, Cu, Ni, Pb, and Zn were concentrated in the fine roots, while Cd was concentrated in the stems. Mangrove plants at Yanbu site contained significantly higher content of all metals than the grown plants in Jeddah and Al-Shuaiba sites, which can be explained by the high metal content in the sediments and the anthropogenic metal sources such as the petrochemical industries, and the industrial and municipal wastewater discharged into this site. Sediment-to-plant transfer coefficients values were higher than unity, which indicate that the mangrove plants have the potential to accumulate the metals. The results highlight a potential risk at Yanbu and Jeddah sites and may help for applying sustainable trials for phyto-management of these lagoons.

Assessment of water contamination by potentially toxic elements in mangrove lagoons of the Red Sea, Saudi Arabia.

Mangrove (Avicennia marina) forests in the Red Sea cost have great concern from environmental, biological, economic, and social points of view. Therefore, assessing water contamination in this ecosystem is worth to be investigated. Consequently, here we aimed to examine the levels of salinity, acidity, and the total content of Fe, Mn, Cu, Zn, Cd, Cr, Ni, and Pb in water samples collected from the upper, middle, and lower part of three mangrove lagoons (i.e., Al-Shuaiba, Yanbu, and Jeddah), Red Sea, Saudi Arabia. The total metal content (µg L-1) in water samples differed significantly among the studied areas and ranged from 286.2 to 4815.0 for Fe, 86.4-483.0 for Mn, 22.9-468.8 for Cu, 199.2-366.6 for Zn, 44.1-99.8 for Cd, 25.6-80.3 for Cr, 11.6-41.5 for Ni, and from 17.7 to 102.0 for Pb. The mean values of Cu, Zn, Cd, and Pb were higher than the WHO water quality standards for fisheries. Water samples in Yanbu were more contaminated and contained higher concentrations of all metals than Jeddah and Al-Shuaiba, due to the petrochemical industries in this industrial area. Our findings suggest that the high metal content in the water of these mangrove sites, particularly in Yanbu, should be considered due to the high potential environmental and human health risks in these ecosystems. These results may help for demonstrating effective approaches for the management of these lagoons. More studies will be carried out on the sediment and mangrove plants in this ecosystem.

Streptomyces pactum addition to contaminated mining soils improved soil quality and enhanced metals phytoextraction by wheat in a green remediation trial.

Streptomyces pactum (Act12), an agent of a gentle in situ remediation approach, has been recently used in few works in phytoextraction trials; however, the impact of Act12 on soil quality and metal phytoavailability has not been assessed in multi-metal contaminated soils. Consequently, here we assessed the potential impact of Act12 on the wheat (Triticum aestivum L.) growth, antioxidants activity, and the metal bioavailability in three industrial and mining soils collected from China and contained up to 118, 141, 339, and 6625 mg Cd, Cu, Pb, and Zn kg-1 soil, respectively. The Act12 was applied at 0 (control), 0.75 (Act-0.75), 1.50 (Act-1.5), and 2.25 (Act-2.25) g kg-1 (dry weight base) to the three soils; thereafter, the soils were cultivated with wheat (bio-indicator plant) in a pot experiment. The addition of Act12 (at Act-1.5 and Act-2.25) promoted wheat growth in the three soils and significantly increased the content of Cd, Cu, and Zn in the roots and shoots and Pb only in the roots (up to 121%). The Act12-induced increase in metals uptake by wheat might be attributed to the associated decrease in soil pH and/or the increase of metal chelation and production of indole acetic acid and siderophores. The Act12 significantly decreased the antioxidant activities and lipid peroxidation in wheat, which indicates that Act12 may mitigate metals stress in contaminated soils. Enhancing metals phytoextraction using Act12 is a promising ecofriendly approach for phytoremediation of metal-contaminated mining soils that can be safely utilized with non-edible plants and/or bioenergy crops.

Plant Growth Promoting Rhizobacteria and Silicon Synergistically Enhance Salinity Tolerance of Mung Bean.

The present study explored the eco-friendly approach of utilizing plant-growth-promoting rhizobacteria (PGPR) inoculation and foliar application of silicon (Si) to improve the physiology, growth, and yield of mung bean under saline conditions. We isolated 18 promising PGPR from natural saline soil in Saudi Arabia, and screened them for plant-growth-promoting activities. Two effective strains were selected from the screening trial, and were identified as Enterobacter cloacae and Bacillus drentensis using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry and 16S rRNA gene sequencing techniques, respectively. Subsequently, in a 2-year mung bean field trial, using a randomized complete block design with a split-split plot arrangement, we evaluated the two PGPR strains and two Si levels (1 and 2 kg ha(-1)), in comparison with control treatments, under three different saline irrigation conditions (3.12, 5.46, and 7.81 dS m(-1)). The results indicated that salt stress substantially reduced stomatal conductance, transpiration rate, relative water content (RWC), total chlorophyll content, chlorophyll a, chlorophyll b, carotenoid content, plant height, leaf area, dry biomass, seed yield, and salt tolerance index. The PGPR strains and Si levels independently improved all the aforementioned parameters. Furthermore, the combined application of the B. drentensis strain with 2 kg Si ha(-1) resulted in the greatest enhancement of mung bean physiology, growth, and yield. Overall, the results of this study provide important information for the benefit of the agricultural industry.