Thermal Sensitivity of Legume-rhizobium Interactions: Root Morphogenesis and Variability: A Review

Legumes are vital to food and nutritional security, often referred to as the “poor man’s meat” because of their high protein content. Their role in sustainable agriculture is anchored in Biological Nitrogen Fixation (BNF), a symbiotic process involving rhizobia that is highly sensitive to fluctuation in soil temperature. Soil temperature governs root system architecture (RSA), microbial colonization and enzymatic activity and is a critical determinant of legume productivity. Extreme soil temperatures impair root activity, microbial symbiosis and nitrogen fixation. This synthesis drew from over 91 out of 124 peer-reviewed studies spanning molecular biology, microbial ecology and agronomic interventions. It examines temperature thresholds affecting nodulation kinetics, RSA traits and symbiotic gene expression, including heat shock proteins (HSPs), cold responsive genes (e.g., GmFRI-1) and hormonal signalling pathways. RSA traits such as root elongation, branching, biomass and vascular development are temperature sensitive, with optimal performance between 20–30°C. Cold stress delays nodulation and reduces nitrogenase activity (~60% at 4°C), while heat stress damages root tip and reduces nitrogenase reductase (~42%). Molecular responses include disrupted auxin transport and HSP induction. Thermotolerant rhizobial strains, Nod factors and inoculation strategies support symbiosis. Agronomic practices such as mulching, conservation tillage and strategic sowing buffer soil thermal regimes and enhance microbial activity. Managing the thermal sensitivity of the legume-rhizobium system through integrated genetic, microbial and agronomic strategies are vital for climate resilient legume cultivation and sustained productivity under variable soil temperature regimes.