Mulching and Cover Crops Effects on the Soil and Rhizosphere-associated Bacterial Communities in Field Experiment

Agricultural sustainability is closely related with the efficient use of natural resources, which are primarily transformed by the action of microorganisms. Soil microorganisms are usually used as early indicators of soil quality since they rapidly respond to changes in soil management. A field experiment was carried out aiming to evaluate the effect of siratro (Macroptylium atropurpureum), bahiagrass (Paspalum notatum) and mulching on the bacterial communities of bulk soil and rhizoplane of siratro and bahiagrass. DNA was extracted directly from soil samples and from bacterial cells of siratro and bahiagrass rhizoplane and analyzed by Denaturing Gradient Gel Electrophoresis (DGGE). Results showed that bacterial communities were affected by both types of cover crop (siratro, bahiagrass and mulch) and the evaluated compartment (soil and rhizoplane). However, the greatest similarity (76%) was observed between bacterial communities of the samples under mulch and bahiagrass rhizoplane. The cluster analysis based on operational taxonomic units (OTU) showed that rare bands were preferentially related to mulch treatment. The diversity of bacterial community of the mulch treatment was 19% and 36% greater than the bacterial communities of siratro and bahiagrass, respectively, as revealed by Shannon-Weaver index. Besides, bacterial community diversity of the soil was 12% greater than that of the rhizoplane. These results indicate a clear effect of the rhizoplane on the selection of the bacterial community, leading to lower diversity index as compared with mulch samples.