There is growing concern about sustainability of commercial eucalyptus plantations in Brazil. This is because, in 99% of the cases, these commercial plantations are monocultures. This practice can cause an imbalance of nutrient contents in soil and of nutrient cycling, e.g. we know that this crop requires high N apports after one or two rotations. Thus, the insertion of a leguminous plant in a mixed system with Eucalyptus has become a relevant option, mainly for soil enrichment with N. Although mixed plantations are generally more productive than pure Eucalyptus stands, there are no studies evaluating the soil and litter microbiome for N-fixing bacteria in mixed Eucalyptus grandis and Acacia mangium plantations. Our research project, however, has the objective of sequencing the 16S rRNA genes of bacteria and archaea in soil and litter, in an attempt to understand the main taxonomic and functional groups of the associated soil microbiota. We expect to find relevant ecological data to prove that nitrogen fixation is the most outstanding trait to differ pure and mixed plantations. With a better understanding of the interactions between Eucalyptus and N-fixing leguminous trees, probably modulated by the diazotrophic character of the latter one, it will be possible to design better management and conservation practices of these forests. This will also enable us to explain how the ecological intensification of intercropped plantations influences soil quality, N cycling, and sustainability of Eucalyptus plantations in Brazil.
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