Woody Mimosa species are nodulated by Burkholderia in ombrophylous forest soils and their symbioses are enhanced by arbuscular mycorrhizal fungi (AMF)

Mimosa is one of the largest genera in the Fabaceae, and includes several trees. They form symbioses with rhizobia and arbuscular mycorrizhal fungi (AMF), which improve nutrition and growth of host plants. Our objective was to analyze the tripartite symbiosis in two woody Mimosa species, and the natural occurrence of their symbiotic microorganisms in soils. Mimosa scabrella and M. bimucronata were grown in trap cultures using soils from Araucaria forests under three management systems: native, planted, and regenerating forest. Bacteria and AMF spores were isolated, identified and their symbiotic efficiency tested. The Mimosa species trapped beta-rhizobia (Burkholderia), putative endophytic bacteria (Pseudomonas, Herbaspirillum, and Xanthomonas), and AMF (Acaulospora, Ambispora, Gigaspora, Glomus, Paraglomus, Scutellospora, and Racocetra). The soils of the different forest managements led to distinct nodule bacterial diversity and AMF sporulation, but a predominance of Burkholderia and Acaulospora spp. was still observed in all areas. Some isolates showed potential to be used as inoculants, and higher nodulation in the presence of AMF was observed. Since different plant growth rates using different soils and microbial inocula were found, we suggest that the dual inoculation with selected beta-rhizobia and AMF is desirable in reforestation projects involving Mimosa spp.