Effects of agricultural Practices in Soil Bacteria communities

FIGUEROLA ELM; AGARAS, B; VALVERDE C; ERIJMAN L; WALL LG

La Falda

Workshop; II TALLER LATINOAMERICANO SOBRE RIZOBACTERIAS PROMOTORAS DEL DESARROLLO VEGETAL; 2014

UNQ-UNRC-UN de Antioquía

No-till is a conservation farming practice adopted in several parts of the world to cope with soil erosion, increase carbon storage and make a more efficient use of available moisture. However, farmers? experience suggests that reduced tillage needs to be coupled with crop rotation and good agrochemical management to be sustainable. The public-private consortium BIOSPAS (www.biospas.org) was created to evaluate the effects of this practice on the biology and productivity of soils. Soil and rhizosphere samples were obtained in Summer and Winter during 2010 and 2011 in no-till soils managed with two contrasting practices (high or low crop rotation), and a grassland as control, replicated in four geographical sites -with different soil textures- located across a regional scale of 400 km in the Argentinean Pampas. Viable pseudomonads were counted on Gould?s S1 selective plates and fluorescent colonies were enumerated under UV light. These plates bearing the most abundant pseudomonads from each sample, served as DNA source to carry out community structure analysis of oprF and gacA genes, formerly reported as Pseudomonas genus markers, by means of PCR-RFLP. The ratio between total pseudomonads and heterotrophic bacteria was higher in high than in low crop rotation plots. Diversity indexes calculated from RFLP patterns of period 2010 were higher in summer samples than in winter ones. oprF PCR-RFLP profiling showed a seasonal grouping, as MDS analysis of RFLP patterns separated summer from winter samples. Thus, this particular group did not modified diversity because of soil management but change its abundance in soil and consequently in plant rhizosphere. In order to look for bacterial community structure including culturable and non culturable groups, a fragment of the v4 region of 16S rRNA gene was high-throughput sequenced after amplification from soil DNA samples. Unlike local diversity (α), which was not significantly affected by land use, agricultural management had a strong influence on β-diversity patterns. The higher phylogenetic relatedness of bacterial communities in soils under monoculture across the region were homogenized and likely determined by the observed loss of endemic species, and affected mostly to phyla with low regional diversity, such as Acidobacteria, Verrucomicrobia and the candidates phyla SPAM and WS3. With the aim of looking for potential indicators of soil quality related to contrasting agriculture management, Tag-encoded pyrosequencing was used to deeply sample the V1-V3 variable region of 16S rRNA gene from bacteria residing in soils corresponding to the three treatments at the four locations. A statistically supported approach was used to define candidates for management-indicator organisms, subsequently validated using quantitative PCR. The ratio between the normalized abundance of a selected group of bacteria within the Acidobacteria GP1 group and the genus Rubellimicrobium of the Alphaproteobacteria may serve as a potential management-indicator to discriminate between sustainable vs. non-sustainable agricultural practices in the Pampa region. These results suggest that the implementation of good agricultural practices, including crop rotation, may be critical for the long-term conservation of soil biodiversity.