Beneficial microorganisms in sites under interference of iron ore mining at Eastern Amazon

Abstract

Soil microorganisms and their interaction with plants are key components in the proper functioning of terrestrial ecosystems. Specifically, arbuscular mycorrhizal fungi (AMF), legume-nodulating nitrogen-fixing bacteria (LNNFB) and endophytes are driving fo rces for the establishment of plants in different environments and, therefore, for the environmental recovery of degraded ecosystems. In order to know ecological aspects of these microbial groups in the ferruginous ecosystems of the eastern Brazilian Amazo n, the present study proposed to evaluate them in three sites of iron mining in the Serra Norte of FLONA of Carajás, State of Pará. For this, two works were developed on mining sites Sandstone II, II Northwest and South IV. The first study aimed to evaluat e the effect of rehabilitation on the AMF communities, and their relation with the main chemical and physical soil properties, selecting areas not rehabilitated, rehabilitated and native within each site. In general, there were high density and diversity o f AMF, mycorrhizal colonization rates, as well as increased levels of glomalin with the progress of rehabilitation, with particularities within each site. The main soil properties related to mycorrhizal variables were pH, soil texture, organic matter content and CEC. In conclusion, the rehabilitation actions carried out at the iron ore sites studied provide the recovery of the AMF communities, process still in progress, especially for the Northwest II and South IV sites with less time of intervention and more difficult management, when compared with Sandstone II. The second study proposed to know, isolate and characterize cultural and genetically the LNNFB and endophytic nodule bacteria in the native areas of the three mining sites. For this, capture experiments were carried out with Macroptilium atropurpureum and Mimosa acutistipula var. ferrea as trap plants, obtaining nodulation only in the first one. The higher efficiency of the bacterial communities of the M. atropurpureum nodules was observed in Sandstone II, expressed by the higher nodulation, biomass production and nitrogen sufficiency index. Fifty-two bacterial strains (including symbiotic and endophytic) were obtained: 32 in Sandstone II, 12 in Northwest II and eight in S-IV. The main noduliferous genus found in the three areas was Bradyrhizobium, while Paraburkholderia was recorded only in Sandstone II. In both cases, the nodD1 nodulation factor was amplified. Endophytic bacteria of the genus Paenibacillus, Enterobacter, Leifsonia and Methylobacterium were isolated from the nodules. The four endophytic genera were found in Sandstone II, Leifsonia and Methylobacterium in Northwest II and Paenibacillus and Methylobacterium in South IV. Finally, the greater diversity and efficiency of LNNFB and endophytic nodule bacteria was observed in Sandstone II. It is also available 31 nodulating strains and 21 endophytic strains for future investigations. In summary, the present study provides basic knowledge about key beneficial microorgan isms in degraded, rehabilitated and native ferruginous ecosystems of the Brazilian eastern Amazon. It is a starting point for new research in the region and provides native bacterial strains for study and evaluation of their biotechnological potentialities.