Diversity and composition of nitrogen fixing communities in Argentinian soils as affected by agricultural practices

O. M. AGUILAR; COLLAVINO M.M; JAMES H. TRIPP; PRISCILA A. CALDEROLI; MARÍA L. VIDOZ; M. DONATTO; JONATHAN P. ZEHR

Copenhagen

Simposio; XIV International Symposium on Microbial Ecology (ISME); 2012

International Society for Microbial Ecology

Microbial community may have significant impacts on important soil processes: however, there is still information about the effect of crop management on the diversity and composition of soil microbial community. In this study, we examined the diazotroph community in Argentinean soils subjected to different agricultural practices (crop rotation with nutrient amendment, monocropping without nutrient, reposition, and non-cultivated soil), using nifh gene as a molecular marker. DNA was extracted from soil samples collected at four sites in Argentina: Pergamino (province of Buenos Aires), Viale (province of Entre Rios, Bengolea and Monte Buey (province of Córdoba). The diversity and composition of diazotrophic community were analyzed by deep pyrosequencing of nifh sequences, the relative abundance by qPCR whereas the active diazotroph populations were assessed by nifh mRNA analysis after reverse transcription. About 183.000 read were processed and short sequences, putative chimeras and frameshifts were removed. The resulting ARB database consisting of 87020 reads was grouped into 1558 OTUs assuming a level of dissimilarity of 0.02% at amino acid sequence level. Comparison of these sequences with the public nifh database, showed that de OTUs indentified in Argentinean soils were distributed among the four major lineages (clusters I to IV) known to exist throughout the world in various environments. This indicates that a broad range of diversity is represented in our ARB database in Argentinean soils. Cluster I was most highly represented in our samples, particularly subclusters 1K and 1J (42% and 20%, respectively), which contain sequences mainly belonging to the orders Rhizobiales and Burkholderiales. Different estimators were applied to assess richness and evenness of the community. Both components showed different degree of diversity; however Bengolea, which represents the sandiest soil, rendered the lowest values independently of the year and treatment. In each location of sampling, richness was in general high in cultivated treatments, except in intensive rotation treatments under corn where the diversity was significantly lower. These results suggest that the diversity of the nitrogen fixing community is affected by soil type, agronomic practices and, particularly, by the crop species used in the rotation. In contrast, analysis of RNA revealed that non-cultivated (pristine) soil displayed higher diversity as compared to cultivated soils. Associations between the diazotrophic communities and treatments were searched by Principal coordinates analysis (PCoA) and cluster analysis (CA) using distance matrices constructed with the OTUs data (abundance and presence-absence). It was found in general, that different locations showed distinctive diazotrophic community. In addition, OUT abundance in each site was significantly affected by the treatment. In conclusion, these results show that diversity, composition and functionality of the diazotroph community varies among soils from different locations, as well as in soils with different agricultural practices.