Biochar and metal-tolerant bacteria in alleviating ZnO nanoparticles toxicity in barley.

The constant use of zinc oxide nanoparticles (ZnO NPs) in agriculture could increase their concentration in soil, and cause a threat to sustainable crop production. The present study was designed to determine the role of spore-forming and metal-tolerant bacteria, and biochar in alleviating the toxic effects of a high dose of ZnO NPs (2000 mg kg-1) spiked to the soil (Haplic Chernozem) on barley (Hordeum sativum L). The mobile compounds of Zn in soil and their accumulation in H. sativum tissues were increased significantly. The addition of biochar (2.5% of total soil) and bacteria (1010 CFU kg-1) separately and in combination showed a favorable impact on H. sativum growth in ZnO NPs polluted soil. The application of bacteria (separately) to the contaminated soil reduced the mobility of Zn compounds by 7%, due to loosely bound Zn compounds, whereas only biochar inputs lowered Zn mobile compounds mobility by 33%, even the combined application of biochar and bacteria also suppressed the soil Zn mobile compounds. Individual application of biochar and bacteria reduced the Zn plant uptake, i.e., underground parts (roots) by 44% and 20%, and in the above-ground parts of H. sativum plants by 39% and 13%, respectively, compared to ZnO NPs polluted soil treatments. Biochar, both separately and in combination with bacteria improved the root length by 48 and 85%, and plant height by 53 and 40%, respectively, compared to the polluted control. The root length and plant height decreased by 52 and 40% in ZnO NPs spiked soil compared clean soil treatments. Anatomical results showed an improvement in the structural organization of cellular-sub-cellular tissues of root and leaf. The changes in ultrastructural organization of assimilation tissue cells were noted all treatments due to the toxic effects of ZnO NPs compared with control treatment. The results indicate that metal-tolerant bacteria and biochar could be effective as a soil amendment to reduce metal toxicity, enhance crop growth, and improve soil health.

Assessing the toxicity and accumulation of bulk- and nano-CuO in Hordeum sativum L.

The effects of bulk- and nano-CuO were monitored on barley (Hordeum sativum L.) in hydroponic conditions. The anatomical and cyto-/morphometric parameters of plants, exposed to both types of CuO in different doses (300 and 2000 mg/L) were recorded. The germination rate, root and shoot lengths decreased in a dose-dependent manner. Exposure to nano-CuO significantly increased Cu content in the H. sativum roots; however, the translocation rates of dissolved Cu were low and showed less accumulation in above-ground tissues. The differences between nano- and bulk-CuO treated plants were sufficiently evident, but at lower concentrations, these differences were non-significant. The relative seed germination inhibition was noted up to 11% and 22% under the high dose of bulk- and nano-CuO, respectively; however, at low dose, it was non-significant. The relative root length was reduced 3.6 fold by bulk- and 1.5 fold by nano-CuO, and shoot lengths decreased 1.6 fold by bulk- and 1.4 fold by nano-CuO under the high dose after growth of 30 days. It indicated more morphological effects on H. sativum caused by bulk- than the nano-CuO. The cytomorphometric analysis indicated the average cortex cell, total cortex, and total central cylinder areas of root cells and the average areas of chlorenchyma leaf cells were increased as compared to control in both bulk- and nano-CuO treated plants. It showed destructive effects of nano- and bulk-CuO on cellular organizations of H. sativum anatomy. Thus, at the low dose, the minimal effects of nano-CuO were observed than the bulk. Therefore, the finding could be interest for the safe application of nano-CuO.