Characterization of Selenium Enrichment in Soybean and Its Relationship with Rhizosphere Microbial Communities in Se-Enriched Saline Soil

Selenium (Se) is an essential trace element for the human body, primarily obtained from dietary sources. The unique characteristics of Se-enriched saline–alkali soils provide valuable insights into how plants absorb and accumulate Se. The present study collected and analyzed soybean plants and rhizosphere soil samples from typical Se-enriched saline–alkali areas in Xinjiang, China to investigate how Se-enriched saline–alkali soil and the associated rhizosphere microbial community influence Se absorption in soybeans. Soybean seeds were the primary site of Se accumulation, with the Se content in the seeds being significantly correlated with that in roots (R2 = 0.4926). The Se content in soybean roots and seeds increased with the total Se soil content, and a significant correlation was observed between them. Additionally, the available Se content in the soil was significantly correlated with the total Se content (R2 = 0.4589). Soil factors such as Na+ concentration, pH, and organic matter (OM) were found to influence the structure of the microbial communities. Furthermore, higher abundances of Proteobacteria, Bacteroidota, and Bacillota in the soil were found to mitigate salt stress and enhance Se absorption in soybean plants. Thus, the rhizosphere microbial community significantly enhances soybean Se uptake. This study provides valuable insights into the mechanisms of Se accumulation in soybeans cultivated in Se-rich soils and offers guidance for cultivating Se-enriched crops. However, this study failed to quantify the differential impacts of different Se forms, such as selenite (SeO42−) and selenate (SeO32−), on microorganisms and plants. Future research should incorporate a detailed analysis of different Se forms to provide more in-depth insights into these complex interactions.