The Impact of Heavy Metal Accumulation on Some Physiological Parameters in Silphium perfoliatum L. Plants Grown in Hydroponic Systems

Bioaccumulation Capacity of Onion (Allium cepa L.) Tested with Heavy Metals in Biofortification

On a worldwide scale, A. cepa is among the most commonly consumed vegetables. In Europe, the leading onion producers are Russia, the Netherlands, Spain, Poland and Germany. In this study, the bioaccumulation of heavy metals (Cr, Cu, Zn, Ni, Fe, Mn, Co, Sr, Cd and Pb) by Allium cepa L. plants was followed under hydroponic conditions. The heavy metals were applied at six concentrations (0, 25, 50, 100, 200 and 400 mg L-1) over three weeks. The quantitative analysis of selected heavy metals in plant tissues (bulbs, roots and assimilation leaves) was performed using atomic absorption spectrometry with flame atomization (F-AAS). The accumulation of metal ions was strongly dependent on their concentrations in the solution and the analyzed parts of plants. The highest accumulation of metal ions was confirmed for the roots and ranged from 8.48 to 5912.34 µg g-1 DW (dry weight). All parts of A. cepa were characterized by the high accumulation of Mn2+. The lowest accumulation was confirmed for Co2+ in the roots, Pb2+ in the assimilation leaves and Cu2+ in the bulbs of onion. Moreover, the study showed that the highest concentrations of heavy metals decreased the growth of bulbs and even caused them to die off. In contrast, lower concentrations of some elements stimulated plant development.

Potential role of apple wood biochar in mitigating mercury toxicity in corn (Zea mays L.)

Mercury (Hg) is a very toxic decomposition-resistant metal that can cause plant toxicity through bioaccumulation and oxidative damage. Biochar, derived from organic waste and agricultural garbage, is an on-site modification technique that can improve soil health in heavy metals-polluted regions. The present experiment was designed to explore the role of apple biochar in the management of mercury toxicity in corn (Zea mays cv. 'PL535'). Different levels of biochar derived from apple wood (0%, 2.5%, 5.0%, and 7.5% w/w) along with different Hg concentrations (0, 20, 40, and 60 mg/L) were used in the experiment that was based on a completely randomized design. Based on the results, HgCl2 at all rates reduced root and shoot dry weight and length, tolerance index, chlorophyll a and b content, the Hill reaction, and dissolved proteins and increased shoot and root Hg content (up to 72.57 and 717.56 times, respectively), cell death (up to 58.36%), MDA level (up to 47.82%), H2O2 (up to 66.33%), dissolved sugars, and proline. The results regarding enzymatic and non-enzymatic antioxidants revealed increases in total phenol and flavonoids content (up to 71.27% and 86.71%, respectively), DPPH free radical scavenging percentage, and catalase (CAT) and ascorbate peroxidase (APX) activity (up to 185.93% and 176.87%, respectively), in corn leaves with the increase in the Hg rate applied to the culture medium. The application of biochar to the substrate of the Hg-treated corns reduced Hg bioavailability, thereby reducing Hg accumulation in the roots (up to 76.88%) and shoots (up to 71.79%). It also reduced the adverse effect of Hg on the plants by increasing their shoot and root dry weight, photosynthesizing pigments, Hill reaction, and APX activity and reducing cell death, H2O2 content, and MDA content. The results reflected the capability of apple wood biochar at all rates in reducing Hg bioavailability and increasing Hg fixation in Hg-polluted soils. However, it was most effective at the rate of 7.5%.