Photosynthetic performance and root architecture of soybean co-inoculated with Amazonian microorganism strains are influenced by red mud application

Soil application of red mud (RM), which is a by-product generated during the processing of bauxite into alumina using the Bayer process, with beneficial microorganisms can represent a promising alternative for revegetation of contaminated areas. Nevertheless, to date, there are no studies on their simultaneous application as well as the use of regionalized strains of microorganisms. This study aimed to evaluate the benefits of the application of RM combined with the co-inoculation of soybean with Bradyrhizobium spp. and strains of beneficial microorganisms isolated from the Amazon in soils from contaminated areas. The study was carried out under greenhouse conditions, using co-inoculation of soybean seeds with Bradyrhizobium spp. plus Trichoderma asperellum, Bradyrhizobium spp. plus Bacillus amyloliquefaciens and only with Bradyrhizobium spp. (standard), in soil containing or not RM (1%). Plants growth/biometrics parameters, gas exchange, chlorophyll a fluorescence, nodulation and root architecture were evaluated. The interaction of RM with B. amyloliquefaciens promoted changes in root architecture, increasing the percentage of thin roots (< 1 mm) in length and volume. Moreover, RM application increased the net photosynthetic rate by 8.8%. The variables related to water use efficiency (up to 6.9%), electron transport rate (up to 5.8%) and root volume (up to 23%) were also increased. The results indicate the feasibility of incorporating RM in soils used for revegetation of contaminated areas. RM interaction with B. amyloliquefaciens co-inoculation promoted changes in the root architecture of soybean plants.