Liebig Review: Legume– <i>Rhizobium</i> Symbiosis Under Selenium Fertilization: A Unique Dual Function in the Plant–Soil System

ABSTRACT Background Selenium (Se) plays a vital role as a beneficial element in promoting the production of leguminous plants. It influences legume quality by improving crop nutritive value and contributing to human and animal health. Literature Review This review is timely, as there are gaps in understanding Se–rhizobia interactions in legumes, which are addressed in three sections of this report. First, the plant‐based mechanisms, which include the Se enrichment of grain and forage legumes and the beneficial impact on human and animal health, and Se’s role in boosting nodule‐symbiotic efficiency. Next, how Se alters physiological processes in legume symbiosis, including the modulation of key enzymes (i.e., nitrogenase and uptake hydrogenase), which consequently determine the N 2 ‐fixing capacity. The last section highlights soil‐related factors that affect Se bioavailability in the soil–plant system, highlighting the role of Se in influencing nutrient cycling by enhancing the activities of soil microorganisms. Conclusions This review discusses the dual function of Se in the plant–soil system under legume– Rhizobium symbiosis. Se has been proven to enhance nitrogen fixation capacity and benefit plants by improving growth and yield, which ultimately contributes to enhanced productivity and food security. On the other hand, by introducing Se in combination with rhizobia, Se has a greater impact on soil nutrients (especially N and P), thereby reducing the need for substantial amounts of chemical fertilizers. Thus, Se plays a unique role in improving legume quality and enhancing human and animal health while promoting the sustainability of agricultural lands.