Mucilage produced by sorghum (Sorghum bicolor) aerial roots supports a nitrogen-fixing community

Sorghum (Sorghum bicolor) is a significant crop globally, serving as an important source of food, feed, and fodder, and is increasingly recognized as an energy crop due to its high potential for biomass production. Certain sorghum accessions exhibit prolific aerial root development and produce abundant carbohydrate-rich mucilage after precipitation. This aerial root mucilage bears resemblance to that found in landraces of maize (Zea mays) from southern Mexico, which have previously been found to harbor diazotrophs. In this study, we examined the aerial root development of specific sorghum accessions and investigated the influence of humidity on this trait. Our microbiome analysis of the aerial root mucilage of maize and sorghum revealed the presence of numerous diazotrophs in sorghum mucilage, with Pseudomonadota, Bacillota, and Bacteriodota being the predominant phyla observed. However, the community composition varied significantly depending on the host plant and location. Through acetylene reduction, 15N2 gas feeding, and 15N isotope dilution assays, we determined that these sorghum accessions can acquire approximately 40% of their nitrogen from the atmosphere through these symbiotic associations on aerial roots. The nitrogen fixation occurring in sorghum aerial root mucilage presents a promising opportunity to reduce reliance on synthetic fertilizers and advance sustainable agricultural practices for food, feed, fodder, and bioenergy production.