Chapter 21 - Land Reformation Using Plant Growth–Promoting Rhizobacteria in the Context of Heavy Metal Contamination

Abstract

Our environment is surrounded with toxic substances that affect everything in several forms, especially green plants, which are the lungs of nature but grown in soil. These noxious things pollute one of the most important medium of life in earth known as the rhizosphere, which is the largest habitat of rhizobacteria on Earth. It is found in and around the roots of crop plants, enhance the crop yield by several mechanisms, and remediate the rhizosphere by eliminating the metal contaminants from soil. These metal toxicants are absorbed mainly by accumulation and biotransformation. Metal contaminations in soil is a major result of human activities such as mining and can be differentiated into three categories on the basis of their properties: reactive oxygen species, overcrowding of functional groups of biomolecules, and displacement of functional groups leading to ecotoxicological risks. The ecotoxic effects of heavy metal contamination have the ability to destroy the receptive parts of the plants and rhizospheric microbes, because once they enter in the soil, they adversely affect the food web due to the biomagnifications. The foremost soil pollutants are Al, arsenic, cadmium, chromium, mercury, lead, antimony, and selenium. The removal of soil contaminants using plant growth–promoting rhizobacteria (PGPR) is believed to be more efficient in comparison to the traditional methods because their activity persists and they have a diversity of soil microorganisms to sustain healthy environment. PGPR are known to affect heavy metals in ways such as phosphate solubilization, chelation, acidification, and redox changes ultimately changing the metal speciation, Production of phytohormones, N2 fixation, siderophores, and conversion of nutrients when they are either applied to seeds or incorporated into the soil to complete the phytoremediation process. Thus, the use of rhizobacteria in combination with plants could be a fast-developing field of research for land reform.