Effects of lead accumulation on the Azolla caroliniana-Anabaena association

Growth, gas exchange, and leaf anatomy of Echinodorus grandiflorus (Cham. & Schltr.) Micheli under Pb contamination

Lead (Pb) can be deposited in aquatic environments that are especially subject to pollution due to wastewater and sewage disposal. This study aimed to evaluate the tolerance of Echinodorus grandiflorus (Cham. & Schltr.) Micheli to Pb and changes in growth, gas exchange, and leaf anatomy. Experiments were conducted with E. grandiflorus plants exposed to the following Pb concentrations in nutrient solution: [0; 0.75; 1.5; 3.0 and 9.0 μM Pb (NO 3)2] in a greenhouse for 60 days. At the end of the experiment, the lead concentration, growth, leaf gas exchange, and changes in leaf anatomy were evaluated. There was no mortality of E. grandiflorus plants, and they accumulated higher concentrations of Pb proportional to the concentration of the pollutant in the solution. Pb did not cause significant changes in growth, stomatal conductance, transpiration, and Ci/Ca rate but reduced the photosynthesis in E. grandiflorus. The leaf anatomy showed significant changes in the presence of Pb, reducing the epidermis and chlorophyll parenchyma. E. grandiflorus demonstrated tolerance to Pb, surviving and growing under contamination; however, it negatively modified its leaf anatomy and photosynthesis in the presence of the metal.

Biochemical responses and phytoremediation potential of Azolla imbricata (Roxb.) Nakai in water and nutrient media exposed to waste metal cutting fluid along with temperature and humidity stress

Phytoremediation of metals from water (WM) and nutrient (NM) media exposed to waste metal cutting fluid (WMCF) along with temperature (T) and humidity (H) stress was tested using Azolla imbricata (Roxb.) Nakai. In the absence of WMCF, biomass was higher in NM than in WM during all tests. Surprisingly, opposite results were noted in the presence of WMCF, with growth failing at exposure to > 0.1% and > 0.5% in NM and WM, respectively. Further, correlation analysis of the growth data following WM exposure revealed that biomass was affected positively by T and negatively by H and metal accumulation. Simultaneously, metal accumulation was affected negatively by T and positively by H. The average accumulations of Al, Cd, Cr, Fe, Pb, and Zn across all T/H tests were 540, 282, 71, 1645, 2494 and 1110 mg·kg^-1, respectively. The observed bioconcentration factor indicated that A. imbricata acts as a hyperaccumulator or accumulator of Zn (>10) and as either accumulator (>1) or excluder (<1) of the other metals. Overall, the phytoremediation performance of A. imbricata in multi-metal-contaminated WMCF was high in WM under all environmental conditions. Therefore, the use of WM is an economically feasible approach for the removal of metals from WMCF.

Bisphenol-A incite dose-dependent dissimilitude in the growth pattern, physiology, oxidative status, and metabolite profile of Azolla filiculoides

Bisphenol-A (BPA) is a ubiquitous environmental pollutant affecting the growth and development of aquatic macrophytes. The present study was designed to evaluate the toxic effect of BPA on Azolla filiculoides. The plants were exposed to different concentrations of BPA and the effect was evaluated in terms of plant growth, physiological and oxidative status, responses of the antioxidative system, and changes in key metabolites. The results have shown that BPA (≥ 20 mg L^-1) incites a significant reduction in frond number, frond surface area, and growth rate of the plants along with severe frond damage, membrane peroxidation, and electrolyte leakage. Moreover, at higher concentrations, a significant reduction in the content of chlorophylls and carotenoids was observed, which was further amplified with the duration of treatments. Furthermore, excessive generation of O₂^•- and H₂O₂ invoked the antioxidative machinery under BPA exposure. However, sufficient activity of the antioxidative enzymes was observed in plants treated with ≤ 10 mg L^-1 of BPA. The untargeted metabolome profile revealed modulation of 29 metabolites including amino acids, sugar alcohols, organic acids, and phenolics in response to BPA. An increased amount of asparagine, lysine, serine, tryptophan, tyrosine, and valine after 3 days of BPA exposure indicates their role in providing better stress tolerance. Therefore, the experimental findings suggest that A. filiculoides responds differently to BPA exposure. Higher BPA concentrations (≥ 20 mg L^-1) documented a greater impact in terms of plant physiology and metabolism whereas, the effect was minimal at lower concentrations (≤ 10 mg L^-1).

Phenanthrene stress response and phytoremediation potential of free-floating fern Azolla filiculoides Lam

In this study, the potential of Azolla filiculoides, a freshwater fern species, on phenanthrene phytoremediation and biodegradation was investigated. Furthermore, the effect of phenanthrene on growth performance, photosynthetic activity and biosynthesis, and accumulation of secondary metabolites of A. filiculodes were evaluated. Plants were grown in a nitrogen-free Hoagland and exposed to different phenanthrene concentrations (0, 1, 5, and 10 mg/L). Exposure to 10 mg/L phenanthrene caused a significant reduction (42%) in Azolla filiculoides growth compared to control on day 14. The photosynthetic pigment content of A. filiculoides treated with 1 and 5 mg/L was almost the same as the control, while 10 mg/L phenanthrene was significantly reduced. In comparison to unplanted controls, the biodegradation percentages obtained from the planted growth medium were found to be 88, 69, and 60%, respectively, for the application of 1, 5, and 10 mg/L phenanthrene. Data on plant growth, photosynthetic pigments, secondary metabolite contents, and biodegradation percentages indicated the tolerance level and the effective phytoremediation potential of A. filiculoides for phenanthrene was <10 mg/L. The results indicated that A. filiculoides is highly effective in phytoremediation of low concentrations of phenanthrene pollution in a short time.

Physiological mechanisms of aluminum (Al) toxicity tolerance in nitrogen-fixing aquatic macrophyte Azolla microphylla Kaulf: phytoremediation, metabolic rearrangements, and antioxidative enzyme responses

To investigate the extent of aluminum toxicity tolerance of eco-friendly, fast-growing, fresh water, pteridophytic Azolla-Anabaena symbiotic association in terms of altered physiological signals; Azolla microphylla Kaulf was exposed to 0 (control), 100, 250, 500, and 750 μM AlCl₃, at pH 4.5 for 6 days. The adversity of Al was increased in a dose-dependent manner and the highest was recorded at 750 μM AlCl₃. Despite the significant loss in membrane integrity (80% electrolyte leakage) due to an enhanced generation of H₂O₂, A. microphylla reflected only 50% growth inhibition (fresh and dry weight) at 500 μM AlCl₃ (LD₅₀). However, the average root length of Azolla was drastically reduced at high concentration due to their direct contact with aluminum-containing growth medium. Contrary to this, the whole association maintained moderate chlorophyll, carbohydrate content, photosynthetic efficiency, nitrogen-fixing ability, and nitrogen content at high Al concentration. Probably, growth protection was pertained through significant detoxification of H₂O₂ by employing an efficient antioxidative defense system including antioxidative enzymes (SOD, APX, and CAT) and non-enzymatic antioxidant carotenoids. An enhanced level of phenolics and flavonoids in the root exudates possibly maintained a non-toxic level of aluminum inside the cell (195.8 μg Al/g FW) which makes A. microphylla a suitable pteridophytic plant to not only remove toxic Al from the contaminated sites but also to improve nitrogen status of those regions. Graphical abstract ᅟ.

The aquatic fern Azolla as a natural plant-factory for ammonia removal from fish-breeding fresh wastewater

This study has investigated the potential of an Azolla-Anabaena symbiosis, a marriage between the cyanobacterium Anabaena azollae and the aquatic fern (Azolla), to remove ammonia from freshwater fish breeding areas. Experiments were carried out under artificial light of 20, 70, and 140 μmol m(-2) s(-1). We investigated three different water temperatures for the growing Azolla, ranging from sub-optimal to optimal temperatures (15, 22, and 28 °C). The capability of Azolla to remove ammonia from wastewater was demonstrated, and the highest ammonia concentration tolerated by the symbiosis between Azolla-anabaena without any toxic effect on the aquatic ferns was ascertained. The shortest time taken to remove ammonia from wastes, 2.5 cm deep and at 28 °C, was 40 min. The ammonia removal rate (A RR) was both light and temperature dependent and the highest rate (6.394 h(-1)) was attained at light intensity of 140 μmol m(-2) s(-1) and at a temperature of 28 °C; the lowest (0.947 h(-1)) was achieved at 20 μmol m(-2) s(-1) and 15 °C. The depth of the fish-wastewater pool also affected the A RR with the relation between A RR and the depth being a hyperbolic function.