Root nodulation and growth in nursery garden of Neltuma flexuosa var. depressa (Fabaceae), a framework species for Monte Desert ecological restoration

The effect of different substrates and rhizobacterial inocula on the nodulation and growth of Neltuma flexuosa var. depressa (Fabaceae, Mimosoideae), a typical native shrub from the Monte Desert of Argentina, was investigated in a nursery trial. The substrates used were: native topsoil from the Monte Desert (T0), an artificial substrate formed from silica sands of two different particle sizes (T1), and the same formulation inoculated with Azospirillum brasilense, Pseudomonas fluorescens and Bradyrhizobium japonicum (T2). We evaluated seedlings’ growth, the formation and activity of nitrogen-fixing nodules in the roots, and the symbiotic effectiveness of B. japonicum. Stem length and aboveground biomass were significantly lower in T1 and there were no differences between T0 and T2. The proportion of seedlings that nodulated was similar between substrates treatments (0.85 ± 0.18). However, the number of total nodules (11.68 ± 8.81 vs 2.43 ± 2.22) and active nodules (6.48 ± 6.49 vs 1.17 ± 1.32) was higher in T1 and T2 compared to T0. The presence of B. japonicum inoculum was not observed in the nodules of N. flexuosa var. depressa. This shrub species showed its ability to nodulate across different substrates. The commercial biofertilizer was effective only for growth, but not for the development of nitrogen-fixing nodules. It is essential to advance the knowledge of an inoculum that provides total predictability for nodulation in this species.