A polyphasic approach in the search of microbial indicators associated with different agricultural practices under no-till management.

GUERRERO LD; AGARÁS B; GABBARINI L; DUVAL M; MARTÍNEZ JM; FIGUEROLA ELM; FERRARI A; VALVERDE CF; GALANTINI J; ERIJMAN L; WALL LG

Seattle, EE. UU.

Simposio; 13th International Symposium on Microbial Ecology; 2010

ISME

Background and aims. Microorganisms play a central role in the decomposition of organic matter, nutrient cycling, and plant nutrient availability in agroecosystems. The practice of no-till has been introduced in agricultural production to reduce soil erosion and improve yield. In Argentina, 70 % of cropland is managed by using no-till methods. We present the first results of an interdisciplinary project (BIOSPAS) aimed at understanding how the microbial structure and microbiological processes in soil under no-tillage farming are related to agricultural practices and soil properties. Methods. Three treatments were defined according to land use: 1) Sustainable agricultural management, subjected to intensive crop rotation and nutrient amendment, 2) mono-cropping without nutrient reposition, 3) natural environment. Blocks of treatments were replicated 4 times in agricultural fields that had documented history of no-till management, at sites located across a west-east transect in Argentina´s Pampas region. Each sample was collected in triplicate, as a composite of 4 soil subsamples from 0-10 cm depth collected at 50 m intervals. We estimated the relative abundances and diversity of major taxonomic groups of bacteria using primer-specific quantitative PCR and PCR-DGGE. Pseudomonads were evaluated by quantifying the culturable fraction and by using two molecular markers oprF and gacA. Key soil variables (pH, moisture, organic carbon content, total nitrogen and glomalin fraction) were also surveyed. Multivariate analysis was used to analyze microbial community data. Results. Differences in physicochemical parameters were more consistently related to agricultural practices than bacterial community data. Actinobacteria dominated the bacterial 16S sequences in all samples, followed by Acidobacteria. Patterns of significant differences between treatments were obtained at the broad level of taxonomic resolution examined, but for most taxonomic groups these differences were site-specific. Conclusions. The results indicate that no-till systems may support distinctive bacterial community composition according to land management, although the assessment of potential indicators may not be straightforward.