The Roles of Plant Growth Promoting Microbes in Enhancing Plant Tolerance to Acidity and Alkalinity Stresses

Abstract

Plant growth often occurs under a range of stressful conditions, including soil acidity and alkalinity. Hydrogen ion concentration, which determines pH of the soil, regulates the entire chemistry of plant nutrient colloidal solutions. Beyond certain levels of pH, multiple stresses such as hydrogen ion toxicity, and nutrient imbalance, toxicities and deficiencies are induced in plants. Breeding for stress coupled with suitable agronomic practices has been a way to deal with this situation in agriculture. However, plant growth promoting microbes (PGPM) have shown potential as sustainable plant growth enhancers and have potential to help with a range of stresses in their environment. Considering the long-term evolutionary relationships between plants and microbes, it is probably that much remains unknown about potential benefits of microbes that could be harnessed from PGPM. This article reviews the current understanding of acidity and alkalinity stress effects on plants and various approaches have or could address these stresses. This review provides a detailed account of the current understanding regarding the role of PGPM in acidity and alkalinity stress management, including when agronomic practices and plant breeding are combined. Approaches already evaluated have shown limitations because acidity and alkalinity in soils are gradual and progressive conditions. Greater exploitation of PGPM in this regard, would be interesting to explore as they have the potential to address multiple stresses in a more sustainable fashion. Future crop production will require further breeding for pH stress resistance, but also implementation of microbial technologies that provide enhanced tolerance to pH stress.

Deciphering the Potential of Rhizobium pusense MB-17a, a Plant Growth-Promoting Root Endophyte, and Functional Annotation of the Genes Involved in the Metabolic Pathway

“…Initially, the bacterial isolate MB-17a shows little growth at pH 3, but after attaining pH from 5 to 9, it showed significant growth. It showed that growth increased with a rise in pH, accompanied by a decrease in alkaline pH (Msimbira and Smith, 2020 ). The effect of different pH values on the growth of Rhizobium pusense MB-17a is demonstrated in Figure 2B .…”

Successful Plant Growth-Promoting Microbes: Inoculation Methods and Abiotic Factors

“…Besides inoculum density and inoculation method, plant response to PGPM inoculation depends on root colonization, which varies with microorganism's multiplication and distribution through the rhizosphere, microbial antagonism, soil humidity, pH, temperature, host, root exudates, as well as the plant physiological state (Venturi and Keel, 2016;Hernández-Montiel et al, 2017;Msimbira and Smith, 2020). After inoculation, the decrease in microorganism population, may be related to difficulties in adapting to their new environment.…”

“…The knowledge on physiological characteristics of the microbial inoculant and the host plant is essential to decide the best inoculation method (Strigul and Kravchenko, 2006;Souza et al, 2015;Etesami, 2020). Successful microbial inoculation depends on inoculation method, inoculum density, root colonization, which varies with multiplication and distribution microbes through the rhizosphere, microbial antagonism, plant physiological state, soil humidity, pH, temperature, host, and root exudates (Venturi and Keel, 2016;Hernández-Montiel et al, 2017;Msimbira and Smith, 2020). Microbial inoculants are placed mainly into seeds (Romeiro, 2007;Souza et al, 2015, Arora et al, 2020.…”

“…The beneficial PGPM-plant interaction requires that the microorganisms are able to use root exudates for colonizing roots, quickly proliferate, compete with the native microbiota and adapt to environmental changes to mitigate abiotic stresses in plants (Souza et al, 2015;Hernández-Montiel et al, 2017;Mimmo et al, 2018;Msimbira and Smith, 2020).…”

Microbial Derived Compounds, a Step Toward Enhancing Microbial Inoculants Technology for Sustainable Agriculture

“…Use of PGPM, as inoculants, in crop production is a common and old practice ( Bashan et al, 2014 ) in many parts of the world, for increased productivity and sustainability ( Babalola and Glick, 2012 ). There is currently a substantial number of promising microbial inoculants, some already on the market ( Velivelli et al, 2014 ; Mehnaz, 2016 ; Berninger et al, 2018 ; Arthur and Dara, 2019 ), with various mechanisms of enhancing crop growth, ranging from growth stimulation, to enhanced defense against pathogens and abiotic stress ( Barea, 2015 ; Gupta et al, 2015 ; Bender et al, 2016 ; Msimbira and Smith, 2020 ; Naamala and Smith, 2020 ). Despite their undisputable success in enhancing crop production ( de Boer et al, 2019 ; Lyu et al, 2020 ), the use of PGPM technology, in crop production, has been constrained by a number of limitations, most notably, inconsistencies, especially under field conditions.…”