Rhizosphere Engineering With Plant Growth-Promoting Microorganisms for Agriculture and Ecological Sustainability

Abstract

The rhizosphere is undoubtedly the most complex microhabitat, comprised of an integrated network of plant roots, soil, and a diverse consortium of bacteria, fungi, eukaryotes, and archaea. The rhizosphere conditions have a direct impact on crop growth and yield. Nutrient-rich rhizosphere environments stimulate plant growth and yield and vice versa. Extensive cultivation exhaust most of the soils which need to be nurtured before or during the next crop. Chemical fertilizers are the major source of crop nutrients but their uncontrolled and widespread usage has posed a serious threat to the sustainability of agriculture and stability of an ecosystem. These chemicals are accumulated in the soil, drained in water, and emitted to the air where they persist for decades causing a serious threat to the overall ecosystem. Plant growth-promoting rhizobacteria (PGPR) present in the rhizosphere convert many plant-unavailable essential nutrients e.g., nitrogen, phosphorous, zinc, etc. into available forms. PGPR produces certain plant growth hormones (such as auxin, cytokinin, and gibberellin), cell lytic enzymes (chitinase, protease, hydrolases, etc.), secondary metabolites, and antibiotics, and stress alleviating compounds (e.g., 1-Aminocyclopropane-1- carboxylate deaminase), chelating agents (siderophores), and some signaling compounds (e.g., N-Acyl homoserine lactones) to interact with the beneficial or pathogenic counterparts in the rhizosphere. These multifarious activities of PGPR improve the soil structure, health, fertility, and functioning which directly or indirectly support plant growth under normal and stressed environments. Rhizosphere engineering with these PGPR has a wide-ranging application not only for crop fertilization but developing eco-friendly sustainable agriculture. Due to severe climate change effects on plants and rhizosphere biology, there is growing interest in stress-resilient PGPM and their subsequent application to induce stress (drought, salinity, and heat) tolerance mechanism in plants. This review describes the three components of rhizosphere engineering with an explicit focus on the broader perspective of PGPM that could facilitate rhizosphere engineering in selected hosts to serve as an efficient component for sustainable agriculture.

Can Inoculation With the Bacterial Biostimulant Enterobacter sp. Strain 15S Be an Approach for the Smarter P Fertilization of Maize and Cucumber Plants?

“…The biostimulant strain 15S used in this work was previously reported by Zuluaga et al ( 2020 ) to have the ability to produce auxins and solubilize Pi. Bacteria-derived auxins are well-known for promoting morphological and physiological processes in plants, leading to increased growth of the root system in terms of root length and surface area; thus enhancing nutrient and water uptake (Hakim et al, 2021 ). Under stressful conditions (e.g., P deficiency), plants can stimulate bacteria to produce auxins (Kudoyarova et al, 2019 ).…”

Common Bean Yield and Zinc Use Efficiency in Association with Diazotrophic Bacteria Co-Inoculations

“…The inoculation of diazotrophic bacteria, especially Zn solubilizing bacteria, play an outstanding role in maintaining a sustainable and eco-friendly environment [28]. This micro-biota biodiversity adopts several mechanisms to not only regulate the environmental cause but also improve plant growth, physiology, and yield, with a better accumulation of nutrients in grains for human benefits [48,64,68].…”

Rhizosphere Bacteria in Plant Growth Promotion, Biocontrol, and Bioremediation of Contaminated Sites: A Comprehensive Review of Effects and Mechanisms

“…The siderophores create Fe competition in the rhizospheric zone, which decreases pathogenic microbe abundance [ 114 , 118 ] and increases plant growth. Siderophores produced by PGPR improve plant Fe uptake and reduce the growth of pathogens by showing a high affinity for rhizospheric Fe 3+ and retaining almost all free iron [ 119 ].…”

“…Roots play an important role in the uptake of essential nutrients needed for plant growth and survival. In the rhizosphere, aggressive root colonization enhances plant growth, which is indicative of positive root–rhizosphere–rhizobacterial interaction [ 119 ]. Moreover, several rhizobacteria produce one or more types of phytohormones in the rhizosphere ( Table 1 ) that also activate phytohormone-producing genes through organic compounds abundant in the root cap and the elongation region [ 145 , 148 ].…”