Synergistic Effects of Different Biochar and Fungi (Glomus Mosseae) in Bioremediation of Metals Contaminated Soil and their Impact on Plant Growth

Abstract

Deterioration of soil and associated crop productivity losses have been one of the major concern all over the world. Contamination of heavy metals in agricultural soils has been interrelated with significant declines in crop yields in Pakistan. Various biotechnological methods are being under investigation in order to address the aforementioned issues specifically biochar based soil amendments. In the current research, the role of biochar in the improvement of plant growth and development was investigated under the combined effect of Arbuscular Mycorrhizal Fungi (Glomus mosseae) and heavy metals contamination. For this purpose, in the first phase, three different biochar were prepared using Zea maize waste, eucalyptus waste and tea waste at 700°C in a muffle furnace heating for 2 hours under anaerobic conditions. The produced biochar was physico-chemically characterized by pH, Electrical Conductivity (EC), FTIR, XRD, SEM-EDX, proximate analysis, elemental analysis, macro and micro-nutrient analysis and thermogravimetric analysis. In the second phase, Different concentrations of biochar (BC) i.e., 0%, 1.5%, and 3% w/w, along with three different rates of Cd, Cr levels: 0, 10, and 20 mg/kg each and Ni levels 0, 20 and 40 mg/kg were used in pot culture experiments. Wheat, Zea Maize and alfalfa plants were grown in these treatments. Post harvesting analyses were performed such as, plant length, fresh and dry biomass, metals analysis and roots characterization. In the 3rd phase, the microbial colonization pattern of plant rhizosphere soil was investigated. Tea waste biochar had maximum pH of 10.68 respectively. The used biochar in this study had optimum EC, The total C for all characterized biochar is 77.8%, 84.82% and 61.82% respectively. Some major and different functional groups (carboxylic groups (C=O) hydroxyl groups) through FTIR were observed in biochar. The XRD spectra confirmed the presence of calcite (CaCO3), and sylvite (KCl). TGA analysis of all biochar indicated that the mass of biochar was lost at four different stages from 0 to 900°C. SEM micrographs of all biochar developed high porosity, presenting different longitudinal pores ranging from micro to macro pores. Fresh and dry biomass of wheat plant was enhanced by 25.11% and 55.86% at 3% and 1.5% BC+ Glomus mosseae+20 mg Cd and 10 mg Cd respectively. The Cd uptake by wheat plant shoots was reduced in the treatments of Zea maize waste biochar by 51.1% and 48.77% at 1.5% and 3% BC. And the Cd was immobilized by biochar in wheat plant roots by 23.16% and 51.18% at 1.5% and 3% BC amendments. The Cr xiv uptake by Zea maize plant shoots was reduced by 75% both at 1.5% and 3% BC applications. The Cr uptake by the plant roots was decreased through the eucalyptus waste biochar by 39.18% and 53.86% at 1.5% and 3% BC. The Ni uptake by the alfalfa shoots was reduced through 1.5 and 3% tea waste biochar by 52.94% and 62.74% respectively. The Ni uptake by the plant roots was decreased by 43.92% and 64.64% at 1.5% and 3% BC respectively. The bacterial strains were isolated from wheat and maize plant rhizosphere soils. They were biochemically and molecularly identified through 16S rRNA sequencing. Isolated ZMWB1, ZMWB2 and ZMWB3 had similarity with Bacillus toyonensis, Paracoccus limosus and Brevundimonas diminuta. All isolates were screened for determination of their MIC value and observed that the Bacillus toyonensis and Brevundimonas diminuta isolated from wheat rhizosphere tolerated various Cd concentrations up to 40 mg/kg while Paracoccus limosus isolated from maize rhizosphere soil showed tolerance against varying Cr levels ranging from 0-60 mg. The density of Glomus mosseae spores in wheat plant rhizosphere soil was increased by 68.91% and 67.56% at 1.5% and 3% BC. In maize plant rhizosphere soil AMF density increased by 26.59% and 27.65% at 1.5% and 3% BC. Whereas in the rhizosphere soil of alfalfa plants. The Glomus mosseae spores were increased by 31.14% both at 1.5% and 3% BC. In summation, our results indicated that all biochar and arbuscular Mycorrhizal Fungi (Glomus mosseae) presented positive outcomes as soil amendments for enhancing the wheat plant, Zea maize plant and alfalfa plant productivity, growth and Cd, Cr and Ni immobilization and thus, reducing its bioavailability in the metal-spiked soil to alleviate food security risks.