Insights into biochar and metals tolerant bacteria in alleviating ZnO nanoparticles toxicity in plant

The application of nanoparticles (NPs) is increasing drastically, especially in crop production. The repeated inputs of metal-based NPs in agri-field could increase their concentration in soil, and cause a threat to sustainable crop production. Thus, the present study was designed to determine the role of spore-forming metal tolerant bacteria (MTB) and biochar (B) to alleviate the toxic effects of high dose of ZnO NPs (2000 mg kg-1) on plants (Hordeum sativum L.) spiked to the soil. For detailed evaluation, the five treatments were used such as 1) clean soil, 2) soil+NPs, 3) soil+NPs+MTB, 4) soil+NPs+B and 5) soil+NPs+B+MTB in plastic vessels in triplicate. The addition of MTB and B showed a promising impact on H. sativum growth in combination and individual inputs. The application of MTB to the contaminated soil reduced the mobility of Zn by 7%, mainly due to exchangeable compounds, and B reduced mobility up to 33%, because of a decrease in equally exchangeable, complex, and specifically sorbed forms. The combined introduction of MTB and B reduced most effectively the actual and potential content of Zn compounds in soil. The content of Zn in H. sativum tissues was increased drastically, especially in ZnO NPs contaminated soil. MTB and B in the contaminated soil reduced Zn accumulation in H. sativum roots by 20% and 63%, and in the aboveground tissues by 11% and 68%, respectively, compared to ZnO NPs polluted soil without amendments. The combined application of MTB and B showed the greatest decrease in Zn accumulation in H. sativum tissues. The root length and H. sativum height was decreased by 52% and 40% in contaminated soil. However, the addition of B, both separately and in combination with MTB reduced root length by 48% and 85%, and plant height by 53% and 40%, respectively, compared to polluted control. The anatomical results also showed an improvement in cellular- sub-cellular organelles, especially in chloroplast by B and in combination with MTB. The results indicate that metal-tolerant bacteria and biochar could be an effective soil amendment to decrease metal toxicity enhance crop growth, and improve soil health.

The research was financially supported by the Russian Foundation for Basic Research, project no. 19-34-60041.