Resumo

Sugarcane is one of the most important crop from an economic point of view, environmental and energetics, being very representative for the explanation of sustainability of agroecosystems, carbon cycling and soil biodiversity. Climatic changes and cultural management may influence the participation of microorganisms in biogeochemical cycles and maintenance of productivity. The objective of this work was to evaluate the effect of increased concentrations of CO₂ on the structure and diversity of microbial communities that make up the rhizosphere of sugarcane. Sugarcane plants (variety RB867515) were grown under CO₂ concentrations of 350ppm and 700ppm, applying the methodology of Stable Isotope Probing (SIP) and samples were collected at 2, 4 and 8 days after enrichment with ¹³CO₂. DNA was extracted with Powersoil^TM kit, and further ultracentrifuged (500 ng) in solution of Cesium Trifluoroacetate (CsTFA) at 64.000 rpm for 40 h at 20 ºC. The ¹²C-DNA and ¹³C-DNA were separated by Beckman^TM system, quantified in Qubit^®, purified in isopropanol and amplified with the GenomePlex^® Single Cell kit. The recovered DNA was analyzed by DGGE technique for total fungal (ITS rDNA) and bacterial (16S rDNA) communities. It was also held the amplification of the V6 16S rDNA region through Ion Torrent^TM platform. The bioinformatics and statistical analyses were made using CLCbio, Quiime and R softwares. The results demonstrated that bacteria have assimilated the root exudates 48 hours after enrichment, especially the representatives of the phylum Firmicultes. Along the cross-feeding, the Proteobacteria tended to predominate, followed by phyla Actinobacteria, Acidobacteria, Bacteroidetes and Firmicutes. There was a predominance of α and γ-proteobacteria in 700 ppm atmospheres and 350 ppm, respectively, showing changes in microbial structure due to the increase of atmospheric CO₂. This work was the first to employ the SIP technique to study the composition of the microbial communities associated with the rhizosphere of sugarcane, naming the major responsive groups in the rhizospehere, and also indicating shifts in such assemblies by climate changing parameters.