- Title
- Cadmium immobilization in rhizosphere and plant-cellular detoxification: role of plant growth-promoting rhizobacteria as a sustainable solution
- Creator
- Halim, Md Abdul
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2023
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Food is the major pathway for exposure to cadmium (Cd) from agricultural soils to humans and other living entities; it is a substance that must be reduced urgently and effectively. Plants can select beneficial microbes such as plant growth-promoting rhizobacteria (PGPR) at the expense of root exudates in the rhizosphere. They are excellent and efficient bio-factories that have a significant ability to bio-reduce Cd by adsorption, precipitation, and bioaugmentation. This thesis aimed to explain the rhizo-immobilization of Cd in contaminated soils using a combination of PGPR and plant nutrient-containing fertilizers. In agricultural rhizosphere soil is prominent for controlling the PGPR, which is vital for the influence of Cd phyto-availability and developing the competition for different ions such as hydrogen ions and cations. The formation of positively charged sites can reduce the sorption of Cd at low pH, which might be toxic to PGPR and plant roots. The Cd sorption in this regard plays a crucial role. The distribution coefficient (Kd) of soil is closely linked to soil pH, SOM, and CEC in agricultural soil. The higher values of Freundlich parameters indicated a higher Cd sorption capacity with high pH soil (PTS) and lower in low pH soil (RTS), where PGPR can be applied for plant growth. The soil PTS is much better soil among others in the current experiment for the safe growing of different agricultural crops such as bread wheat, durum wheat, and maize and minimizes the Cd stress. The PTS soil Cd may reduce the plant growth parameters, which is predicted by 50% inhibition concentration (IC50) values of 4.21±0.29 and 4.02±0.95, respectively, whereas the maximum HRI index is 3.85±0.05 and 5.32±0.27, respectively for Triticum aestivum L. cv. Mustang and Triticum aestivum L. cv. Lancer. The plant growth-promoting rhizobacteria (PGPR) (Methylobacterium oryzae CBMB20) increases the activities of plant Cd detoxification enzymes such as CAT, SOD, POD, AsA, GSH, TSS, TPH, and proline in the roots of wheat plants (Mustang) when they are grown in acidic and alkaline soil under Cd stress conditions. Moreover, the PGPR improves the morphology and physiology of the roots of wheat (Mustang) seedlings and functions better in alkaline soil compared to its acidic counterpart. Novel CMC-PEI-8 composites were synthesized to establish the effective reduction of Cd in plant parts in addition to PGPR. The CMC-PEI-8 showed significant adsorption of Cd2+ from an aqueous state and could be well described by the Langmuir model; adsorption capacity achieved 206.81±29.68 mg g-1, which was better than what other reports documented. Simultaneously, good usability in different ranges of pH of the CMC-PEI-8 composites adsorbent offers good suggestions for applicability in agriculture. Then, the composite was synthesized by loading plant essential nutrients such as Ca and P while the micro-composites served to remediate Cd in plant parts. The slow and controlled release of P using these micro-composites was approximately 58.30 mg g–1. The phosphate release kinetics fitted well with the Elovich model. The essential plant nutrients loaded micro-composites were evaluated for Cd remediation from irrigation water, and their essence was assessed in terms of PGPR inoculation and multiplication. The micro-composites showed Cd2+ with 314.0 mg g-1, in Langmuir isotherm equations. In addition, it has great potential for use with PGPR which illustrates the significant practical aspects under Cd stress conditions in the plant soil environment. The modified micro-composite CHP@CMC-PEI, which is regarded as CHP@CMC-PEI , reduces the DTPA-extractable Cd significantly by not altering pH considerably; this is due to the addition of PGPR (Methylobacterium oryzae CBMB20). The combined amendment benefits plant growth and can significantly diminish Cd accumulation in plants. Thus, combining the bacterial PGPR and biogenic CHP@CMC-PEI represents a potential method to reduce Cd in the soil and its accumulation in plants.
- Subject
- cadmium; rhizosphere; plant-cellular detoxification; plant growth-promoting
- Identifier
- http://hdl.handle.net/1959.13/1473322
- Identifier
- uon:48994
- Rights
- This thesis is currently under embargo and will be available from 30.04.2024, Copyright 2023 Md Abdul Halim
- Language
- eng
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