Brazil has featured on the world production of Eucalyptus and is considered the largest producer of this forest essence. However, to maintain high productivity rates, the eucalyptus plantations require high application of nitrogen fertilizers in the soil. Thus, monospecific plantations can exhaust the soil N content in the course of the production cycle. In this way, mixed plantations of eucalyptus and acacia trees have been implanted to maximize the productivity and sustainability of eucalyptus stands. The major interest in acacia occurs due the association of the her roots with very efficient bacteria fix atmospheric N, a process that can reach values greater than 300 kg ha-1 of N fixed annually. This forest plantation type it's a relatively new system introduced in tropical soils conditions and few studies have evaluated the dynamics of microbial community in these systems, especially as species composition can influence the soil microbiome and how it behaves genomics cycling N in this agro-ecosystem. Knowing that insertion of N in the soil is one of the possible benefits of this integration between eucalyptus and acacia trees, the aim of this study is to understand the taxonomic and functional diversity of soil microbiome associated with nitrogen cycling in a first rotation of pure forests and mixed Eucalyptus urograndis and Acacia mangium. We believe that plants of A. mangium can be important in the change process of soil microbial community in mixed plantations with Eucalyptus due to transfer and constant insertion of soil N through biological fixation of N. Moreover, there is a lack information with regard to the role of microbial functional genes and their main player on the N cycle in tropical forest soils. Studies assessing functional genes in situ will help us to understand the biogeochemical cycles performed by the soil microbiome mixed plantations, giving bases to infer about how forest management can influence possible metabolic pathways that are occurring in the soil, filling gaps in scientific knowledge and practical as a better understanding of the cycle N. In this way, we have reasons to incorporate knowledge of the dynamics of microbial communities from the ground to the practice of forestry, improving the management of soil, N application efficiency in the soil of forest plantations, mixed or not.
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