Pyrosequencing analysis of nitrogen fixing communities in soils with different agricultural management.

COLLAVINO MM; AGUILAR O.M

Tucumán

Congreso; VII CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL; 2011

Sociedad Argentina de Microbiología general

Despite the key role of bacteria in soil processes, there is still limited information about the effect of crop management on the diversity of soil microbial community. In this study, we examined the diversity and abundance of the free-living diazotrophic microorganims in soils under different agricultural practices (crop rotation and nutrient amendment, monocropping without nutrient reposition, and non-cultivated soil), using nifH gene as a molecular marker. Soil samples used in this study were collected at two sites, Monte Buey (Córdoba) and Viale (Entre Ríos) as part of the PAE project called “BIOSPAS” (Soil Biology and Sustainable Agricultural Production). The relative abundance of the nitrogen fixers in soil samples was quantified by real-time PCR. The copy number of nifH varied according to the soil type and agricultural management. Viale samples had a higher number of copies than Monte Buey. Moreover, Viale did not show differences related to agricultural practices, whereas Monte Buey soils under monocropping had a higher level of nifH. The nifH sequence diversity found in samples was analyzed by pyrosequencing of nifH, using the GS FLX Titanium platform (Roche). 183,000 reads were obtained, aligned and grouped in Operational Taxonomic Units (OTUs) using the Dotur program. Diversity among samples was analyzed comparatively with different statistic indexes (rarefaction, Chao1 and Ace), considering different degree of sequence dissimilarity (0-10%). In Monte Buey samples, OTU abundance was higher in soils under monocropping practices, followed by those under rotation and finally by non cultivated soil, independently from the taxonomic level used to group them. In contrast, variation in the number of OTUs was found in Viale analysis according to the level of sequence dissimilarity. The monocropping soil samples presented the highest diversity with low levels of dissimilarity (0 to 3%) and the lowest with high level of dissimilarity (5 to 10%). Rarefaction analysis suggests that our sequencing approach has covered approximately 99% of nifH diversity in soils under rotation and in the non-disturbed soils from Monte Buey, while the other soil samples ranged between 65 and 77% revealing the high variability in these samples. In conclusion, these results show that the pattern of diversity and abundance of nifH sequences varies among soils from different locations, as well as in soils with different agricultural management.