Nod factors improve the nitrogen content and rhizobial diversity of faba bean and alter soil dehydrogenase, protease, and acid phosphomonoesterase activities

Nod factors produced by rhizobia are one of the most important signals involved in symbiotic associations involving legumes. A field trial was performed to assess the symbiotic activity, rhizosphere biological parameters, and plant biomass of faba bean (Vicia faba L.) treated with Nod factors. The soil was a Haplic Luvisol derived from loess. The faba bean seeds (cv. Granit) were soaked with an Nod factors solution (260 nM) or water (control) and sown. At the flowering stage, the genetic diversity of rhizobia (based on PCR-RFLP profiles and the sequencing of the 16-23S rDNA and nodD gene), nitrogenase activity (acetylene reduction assay), and nodule biomass were evaluated. Nitrogen yield and plant biomass were determined at the flowering and maturity stages. Rhizosphere soil was examined during plant growth in relation to the activities of dehydrogenase, protease, urease, and acid phosphomonoesterase. The results indicated that the application of the Nod factors improved nitrogenase activity (by 74-80%, depending on the parameter analysed) and increased the genetic diversity of rhizobia inhabiting root nodules, plant nitrogen content (by 16.8%, at maturity), and seed protein yield (by 14.6%). The rhizobial population became more heterogeneous under the influence of the Nod factors than it was for the control (12 and 7 specific genotypes, respectively). At the flowering stage, Nod factors enhanced dehydrogenase, protease, and acid phosphomonoesterase activities by 46, 36 and 9%, respectively. The results revealed the positive effect of Nod factors at reducing water deficiency effects during a growing season with a short-term rainfall deficit.