Mineral Accumulation and Physiological Responses of Two Halophytes, Caroxylon vermiculatum and Mesembryanthemum nodiflorum: Implications for Phytoremediation in Contaminated Coastal Environments.

Halophytes are recognized for their adaptive capacity and potential applications in phytomanagement and ecosystem restoration. This study investigates the comparative physiology and antioxidant responses of two native halophytes, Caroxylon vermiculatum (L.) and Mesembryanthemum nodiflorum L., growing naturally in saline and metal-affected coastal environments. A comprehensive set of physiological and biochemical parameters was assessed, including macro- and microelements (Na, K, Ca, Fe, Zn, Cd), photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids), soluble sugars, and proteins. In addition, oxidative stress markers (hydrogen peroxide, H2O2, and malondialdehyde, MDA), enzymatic antioxidants (superoxide dismutase, SOD, catalase, CAT, and guaiacol peroxidase, GPX), and non-enzymatic antioxidants (total phenolics, flavonoids, and proanthocyanidins) were evaluated. Antioxidant activities, including DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging and reducing power, were also measured. The results revealed clear species-specific adaptive strategies. Mesembryanthemum nodiflorum exhibited higher accumulation of Na and K, together with elevated levels of carotenoids and oxidative stress markers. This species showed translocation factors (TF > 1) for Na (~1.60) and K (~1.90), indicating efficient ion transport to aerial parts, while displaying low bioconcentration (BCF < 0.5 for most trace elements) and biological accumulation factors (BAF < 1), suggesting limited capacity for heavy metal accumulation. In contrast, Caroxylon vermiculatum showed higher concentrations of chlorophylls, carotenoids, phenolic compounds, flavonoids, and proteins, along with stronger superoxide dismutase activity. It also exhibited lower translocation of trace elements (TF < 1) and higher root retention of metals (BCF up to ~0.5), indicating a more effective exclusion and detoxification strategy. Overall, these findings demonstrate that M. nodiflorum relies on ion accumulation and translocation, whereas C. vermiculatum exhibits stronger ion regulation and antioxidant protection. Given the moderate BAF and BCF values observed, both species are more likely to contribute to phytomanagement through ion regulation and phytostabilization rather than efficient phytoextraction.