Iron (Fe) and zinc (Zn) are essential micronutrients for plant metabolism; however, their bioavailability in tropical soils is often limited by low solubility and complex mineral interactions. Root-associated bacteria may enhance micronutrient availability through siderophore production and the solubilisation of insoluble mineral forms. This study aimed to functionally characterise three bacterial isolates from rice roots—Bacillus siamensis TUR07-02b, Priestia aryabhattai SMNCH17-07, and Priestia megaterium SMBH14-02—under controlled in vitro conditions. Siderophore activity was evaluated qualitatively using Chrome Azurol S (CAS) agar, where percentages represent halo-based indices relative to colony diameter, and quantitatively using the CAS–shuttle assay, expressed as percent siderophore units relative to an uninoculated reference. Zinc solubilisation was assessed in solid media as halo-based indices and in liquid media as Zn-equivalent signals (mg L⁻¹) obtained by spectrophotometry. All strains produced siderophores, with P. aryabhattai showing the highest qualitative index (167%), while P. aryabhattai and B. siamensis showed statistically similar activity in liquid medium (~23%). Zinc solubilisation was substrate-dependent: B. siamensis showed the broadest solubilisation spectrum in solid media, whereas P. aryabhattai achieved the highest Zn-equivalent signals for ZnCO₃ and Zn₃(PO₄)₂ after 20 days. These results demonstrate strain-specific functional differences and represent a preliminary screening method based on relative in vitro estimations.

Legumes (Fabaceae) are key functional components of tropical forests due to their role in nitrogen fixation and nutrient cycling. This study provides an integrated assessment of forest legume diversity and its relationship with soil physicochemical properties across three protected areas in the Peruvian upper Amazon: the Alto Mayo Protected Forest (BPAM), the Cordillera Escalera Regional Conservation Area (ACR-CE), and the Shunté and Mishollo Forests Regional Conservation Area (ACR-BOSHUMI). Floristic studies were conducted in nine sectors ranging from 618 to 1729 m a.s.l. Soil samples were analyzed, and vegetation cover was quantified using high-resolution drone imagery with four vegetation indices derived from RGB data. We recorded eleven legume species from eight genera within the sampling plots, identifying Inga as the most frequent genus. Species diversity was highest in the ACR-CE, whereas BPAM showed lower richness and abundance. Multivariate analyses revealed that legume diversity was positively associated with higher soil pH, cation concentrations, and cation exchange capacity, but negatively associated with elevated Al³⁺ and Fe³⁺ levels. Vegetation indices effectively distinguished between vegetated and degraded areas, indicating higher legume occurrence in sites with greater canopy cover. These findings emphasize that soil fertility and vegetation structure are key drivers of legume diversity, with significant implications for conservation in the upper Amazon.