Recently discoveries have shown positive responses in Eucalyptus plantations intercropped with Acacia mangium. The aim of this study was to evaluate the influence of pure and mixed systems (Eucalyptus grandis and A. mangium) on the microbial communities\' structure in soil. We evaluated the structure of these communities in a gradient of soil depth. In this context, deep trenches were digged in pure stands of Acacia (100A), Eucalyptus (100E) and mixed systems (A+E). In mixed forest plantations, soil and roots were sampled at the base of Acacia (A+E) and the base of Eucalyptus (E+A). Soil over 10 layers along the profile from 0 to 800cm were sampled, with 4 replicates each. The microbial communities were monitored by PCRDGGE, where we observed a strong effect of soil depth on microbial communities. As a result, specific clusters were formed in each soil layer. The community composition of Eucalyptus grandis stands was different from the community structure found in the 100A, A (A+E) and E (E+A) systems. The total fungal community did not show any group differentiation due to the plantation system, while the profiles of mycorrhizal fungi (AMF) of these three groups were significantly different from that of the treatment A (A+E). A correlation analysis performed by RDA indicated that the FMA community of the treatment (A+E) was correlated positively with P values in the soil. Another variable quantified was the community of bacteria and fungi, indicated by the number of copies of ribosomal 16S rDNA and ITS, respectively. Comparing the upper soil layers (0-20 cm), we couldn\'t find differences in the abundance of copies of 16S rRNA and ITS region genes in all treatments, but we observed an exponential decrease in 16S rRNA copy numbers with increasing soil depth. Regarding the presence of AMF, we found low root colonization and low abundance of AMF spores in all treatments, although 100E presented higher colonization rates than the others. Altogether, 16 AMF species were found, most of them belonging to the genus Acaulospora. We conclude that these forest systems a plant species seems to be more important than the other in the structuring of the microbial community and that some soil factors may be preponderant in this separation. The processes involving the dynamics of the microbial community structure is a crucial point in understanding the development of forest plantations, mainly by involving the biogeochemical cycles, when seeking for new promising approaches and sustainability parameters. (AU) |
