Ecological Risk Assessment of Potential Toxic Elements in Salt Marshes on the East Coast of the Red Sea: Differential Physiological Responses and Adaptation Capacities of Dominant Halophytes

Abstract

The impact of the mutual interactions between salinity and the phytoavailability of potential toxic elements (PTEs) on the adaptation of halophytes in their natural habitat is complex and far from clear. Herein, we aimed to evaluate salinity- and PTE-induced oxidative stress in selected halophytes and the antioxidant responses of these plants. For that, five salt marshes were selected, and the physiological responses of dominant halophytes (Tamarix nilotica, Heliotropium crispum, Zygophyllum coccineum, Halopeplus perfoliata, and Avicennia marina) were evaluated against the physicochemical features of their rhizosediments. The tested locations varied in their physicochemical properties and showed various levels of salinity stress and a low fertility status. Distinct variations in ten PTE concentrations were recognized among locations and within plants, with Cr and Co showing the highest ecological risk indices. The high levels of salinity and PTEs were associated with higher foliar levels of malondialdehyde, particularly in A. marina and Z. coccineum. The bio-concentration ratio revealed hyperaccumulating potentials of PTEs by the tested halophytes. Z. coccineum showed effective accumulation of Co, Fe, and Pb, while T. nilotica exhibited effective accumulation of Cu, Cd, and Zn. H. perfoliate had higher accumulation of Cr and Hg, whereas A. marina accumulated a significant amount of Hg, Cd, Zn, and Mn. H. crispum leaves accumulated the highest Ni levels among the tested halophytes. Altogether, our results highlight the potential risk of pollution of the tested areas with PTEs and the efficient physiological adaptation of each of the tested halophytes as a unique biological system. They also reflect the high capabilities of the tested halophytes as phytoextractors of their corresponding PTEs and their potential as efficient tools for phytoremediation of salt- and PTE-affected lands.

Physiological and Biochemical Changes in Vegetable and Field Crops under Drought, Salinity and Weeds Stresses: Control Strategies and Management

“…The plants exposed to these factors elicit many reactions and changes in the cells, for example, cellular dehydration, and a decrease in the water availability in the cytoplasm resulting in a reduction of the vacuolar volume [160]. Additionally, one of the early responses is the production of ROS, which negatively affects cellular structures, decreases the photosynthetic rate, and causes hormonal balance disorder as with increasing ABA level [161]. Moreover, compatible solutes, stress proteins and antioxidant components were increased; nevertheless, energy-consuming pathways were suppressed under weeds [39], salinity and drought [162].…”

“…Likewise, under salinity conditions, the large root system can increase the sequestration surface of toxic ions such as Na+ to decrease salt concentration. In this regard, the large root growth in barley plants was associated with enhanced salt tolerance [161]. Another adaptive mechanism during drought stress is the inhibition of the shoot system to increase solute concentration and, consequently, enhance osmotic adjustment [162].…”

Physiological responses (HSH70, Mt), Oxidative stress, toxicity impacts, and risk assessment of the biomarker (Enochrus tenuicosta) to heavy metals contamination along the Red Sea coasts- Egypt.

“…Notably, the levels of Cr, Hg, and Pb were higher than those allowed by the WHO. There is a substantial chance that these heavy metals' high concentrations will enter the human food chain and have cytotoxic, mutagenic, and cancerous impacts on people's health (34). The varied pollution sources in this area may be the cause of the relatively higher heavy metal values in sediments from the Gulf of Suez location than in sediments from Hurghada sites.…”

Comparative Analysis of Organic Extracts Bioactivity from Two Limonium. Mill Species Growing Wild in Tunisian Salty Marshes

“…[1] In these extreme ecosystems, plants display a variety of adaptive behavior including morphological plasticity, [2] prevention of toxic salt ions accumulation, and increasing essential nutrient uptake and primary metabolites supply required for growth and reproduction. [3] Besides, spontaneous species adapted to marginal lands (salt marshes, desert, skeletal soil) are known to produce a diversity of secondary metabolites, which are not directly involved in primary growth but are of high importance for plant resistance to biotic and abiotic, such as high and low temperature, drought, alkalinity, salinity, UV-irradiation, wounding, nutrient deficiencies, and pathogen infection. [4] Actually, more than 100.000 known secondary metabolites including an array of polyphenols, alkaloids and terpenes make up the chemical defense system, [5] which is generally induced upon plant exposure to stress conditions.…”

“…Spontaneous plant species growing wild in constraint habitats, such as salt marshes, have evolved efficient physiological and metabolic traits that enable their survival and tolerance under stressful factors [1] . In these extreme ecosystems, plants display a variety of adaptive behavior including morphological plasticity, [2] prevention of toxic salt ions accumulation, and increasing essential nutrient uptake and primary metabolites supply required for growth and reproduction [3] . Besides, spontaneous species adapted to marginal lands (salt marshes, desert, skeletal soil) are known to produce a diversity of secondary metabolites, which are not directly involved in primary growth but are of high importance for plant resistance to biotic and abiotic, such as high and low temperature, drought, alkalinity, salinity, UV‐irradiation, wounding, nutrient deficiencies, and pathogen infection [4] .…”