JOURNAL of Soil Biology and Ecology

Azospirillum: multifaceted benefits beyond biological nitrogen fixation

Author:

M. K. MURALI AND D. J. BAGYARAJ 

Abstract:

Azospirillum, a prominent plant-growth-promoting rhizobacterium (PGPR), has emerged as one of the most extensively studied microbial inoculants for sustainable agriculture. Although widely known for its associative biological nitrogen fixation (BNF), research over the past three decades has revealed that the ecological and agronomic contributions of Azospirillum extend far beyond nitrogen input. Azospirillum synthesizes a broad spectrum of phytohormones such as indole-3-acetic acid, gibberellins, cytokinins, and ACC deaminase that profoundly influence plant growth regulation, root system architecture, and developmental processes. In addition, the bacterium significantly improves nutrient acquisition through mechanisms including phosphate solubilization, siderophore-mediated iron mobilization, and enhanced root-mediated nutrient uptake. Azospirillum also plays a central role in mitigating abiotic stresses and heavy metal toxicity by enhancing antioxidant activities while simultaneously contributing to biotic stress resistance through induced systemic resistance and enhanced production of defense-related metabolites. Beyond plant–microbe interactions, Azospirillum positively influences soil health by improving microbial diversity, enzymatic activity, and soil structure. Collectively, these multifunctional attributes underscore the significance of Azospirillum as a key microbial inoculant for sustainable, low-input, and climate-resilient agriculture.

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