Diveristy of nitrogen fixing communities in soils with different agricultural management revealed by pyrosequencing analysis

MM. COLLAVINO, JH TRIPP, PA. CALDEROLI, ML VIDOZ, M DONTO, JP ZEHR, O. MARIO AGUILAR

Mar del Plata

Congreso; VIII Congreso de Microbiologia General; 2012

Sociedad Argentina de Microbiologia Genral

Microbial community may have significant impacts on important soil processes, yet, there is still limited 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 Argentinian 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. Soil samples used in this study were collected at four sites: Pergamino (Buenos Aires), Viale (Entre Ríos), Bengolea and Monte Buey (Córdoba) as part of the PAE project ?BIOSPAS? (Soil Biology and Sustainable Agricultural Production). The relative abundance, diversity and composition of diazotrophic community were analyzed by pyrosequencing of nifH sequences using the GS FLX Titanium platform. 183,000 reads were processed and shorts sequences, putative chimeras and frameshifts were removed. The resultant database consisting of 87020 reads was grouped into 1558 OTUs assuming a level of dissimilarity of 0.02% at amino acid sequence level. These sequences, when compared with the publically available nifH database (Zehr et al., 2003), showed that the OTUs identified in Argentinean soils were distributed among the four major lineages. This indicated that the nifH diversity is represented in our database. Soil samples were dominated by sequences from the cluster I, with 40% of total OTUs from 1K, 21% from 1A and 20% from 1J. The most abundant OTUs were similar to genera belonging to Rhizobiales and Burkholderiales orders. Diversity was evaluated as a function of two components, richness and evenness, using different estimators. Independently of the year and treatment, both components showed the lowest values in Bengolea, the sandiest soil. In each location, richness was in general higher 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. The associations within the diazotrophic communities were investigated by Principal Coordinates Analysis (PCoA) and Cluster Analysis (CA) using distance matrices constructed with the OTUs data (abundance and presence-absence). In general, different locations showed distinctive diazotrophic community. In addition, OTU abundance in each site was strongly affected by the treatment.In conclusion, these results show that diversity and composition of the diazotroph community varies among soils from different locations, as well as in soils with different agricultural practices The associations within the diazotrophic communities were investigated by Principal Coordinates Analysis (PCoA) and Cluster Analysis (CA) using distance matrices constructed with the OTUs data (abundance and presence-absence). In general, different locations showed distinctive diazotrophic community. In addition, OTU abundance in each site was strongly affected by the treatment.In conclusion, these results show that diversity and composition of the diazotroph community varies among soils from different locations, as well as in soils with different agricultural practices