Phosphate-Solubilizing Rhizobacteria: Diversity, Mechanisms, and Prospects in Sustainable Agriculture

Abstract

Phosphorus (P) is the second-most important element after nitrogen that is required for plant growth. Although this element is abundant in most soils, it is rarely available in plant-accessible forms since most of it normally exists in soil in insoluble forms such as phosphates. In conventional agriculture, P is normally supplied as chemical fertilizer to satisfy plant P requirements. This, to a large extent, boosts plant production. However, chemical fertilizers are costly, have a huge carbon footprint, and are environmentally-unsustainable owing to the high energy requirements during their synthesis. Besides, P-containing agricultural run-offs contribute hugely to the eutrophication of water bodies and environmental degradation. Moreover, plants can consume only a small amount of chemically-supplied P since between 75 and 90% of this form of P normally get precipitated into complexes and rapidly become fixed in soil. These issues and concerns necessitate research into alternative and viable ways of supplying P to plants. Rhizobacteria have for decades been investigated in vivo and in planta as suitable tools in sustainable agriculture due to the plant-growth-promoting activities such as nutrients’ solubilization, nitrogen fixation, and production of phytohormones. Although a lot of research has been done on different nutrients-solubilizing rhizobacteria and their potential in sustainable agriculture, their mechanisms of action and prospects in sustainable agriculture remain to be fully understood. This review particularly focuses on the P solubilizing rhizobacteria and evaluates their diversity, mechanisms of action, and prospects in sustainable agriculture based on the present and future scenario of their application. Such information is useful in determining their potential and evaluating their prospects in promoting sustainable agricultural systems.

Mechanism of Intermittent Deep Tillage and Different Depths Improving Crop Growth From the Perspective of Rhizosphere Soil Nutrients, Root System Architectures, Bacterial Communities, and Functional Profiles

“…For example, enriched species, such as OUT_143, OTU_85, OTU_483, and OTU_188, were classified into Gp6 , Aeromicrobium , Aquabacterium , and Gemmatimonas . Studies found that Aeromicrobium increased tolerance of host plant to abiotic stress, and improved growth, yield, and biomass ( Martin and Dombrowski, 2015 ); Aquabacterium and Gemmatimonas were found to be phosphate-solubilizing bacteria in Taro and maize rhizosphere ( Yang et al, 2017 ; Aloo et al, 2020 ); Acidobacteria Gp6 was usually present in higher abundance in the nutrient-enriched soil ( Sul et al, 2013 ). Replacing species OTU_431 classified into Gp6 also promoted plant growth and decreased disease morbidity.…”

Prospects for soilless farming in Africa: A review on the aids of plant growth-promoting rhizobacteria inoculants in hydroponics

“…Siderophore production is a typical example of how rhizobacterial inoculants can establish themselves in the rhizosphere and enhance Fe nutrition. Due to its indisputable importance, it should be given more attention (Aloo et al, 2019).…”

Advancement and practical applications of rhizobacterial biofertilizers for sustainable crop production in sub-Saharan Africa

“…Apart from N 2 -fixation, some rhizobacteria can greatly improve plant nutrient uptake through nutrients solubilization [89,104]. Evidence suggests that P solubilization and mobilization which are mediated by most rhizobacteria are invaluable at increasing P availability in agricultural soils [105,106] ) ions which are the only P forms that can be used by plants [107]. The solubilization of organic P by phosphatases and phytases by PSB is referred to as mineralization [104] and may constitute up to 5% of total P in soil [108].…”