Structure and abundance of ammonia-oxidizing bacteria and archaea in no-till soils under contrasting crop management

EVA FIGUEROLA; SILVINA ROSA; LEANDRO GUERRERO; LEONARDO ERIJMAN

San Miguel de Tucumán

Congreso; VII Congreso Argentino de Microbiología General- SAMIGE del BICENTENARIO; 2011

Sociedad Argentina de Microbiología General

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } --> Ammonia oxidation is central to the global nitrogen cycle. It is presently recognized that other group of microorganisms, besides the ammonia-oxidizing bacteria (AOB), are capable of carrying out autotrophic ammonia oxidation. The ammonia-oxidizing archaea (AOA) have widespread distribution in terrestrial environments, suggesting an important role for them in the nitrification process. Whereas both the presence and activity of soil microorganisms are profoundly influenced by the characteristics of the environment where they grow and develop, it is important to analyze whether differences in soil management influence the abundance and activity of these populations, and inversely how does the microbial community structure affect soil quality. This issue has particular ecological relevance when it is addressed within the framework of crop productivity, as assessed by farmers’ records. The aim of this work was to determine the effect of contrasting agricultural management practices on the abundance and structure of AOB and AOA in no-till systems. Four soils with documented history of no-till management located across a west-east transect in the central region of Argentina were taken as the basis for replication. Three treatments were defined according to land use: 1) Sustainable agricultural management, subjected to crop rotation and nutrient amendment, 2) Non-sustainable agricultural management with crop monoculture and reduced nutrient reposition, 3) Non-cultivated areas adjacent to the sampled fields, as references for natural soil environments. To determine the bacterial community structure, ammonia oxidation (amoA) genes were used to fingerprint AOA and AOB soil communities by terminal restriction fragment length polymorphism analysis (t-RFLP). According to canonical correspondence analysis, AOA communities clustered by sampling site. Envfit permutation test showed that correlations between AOA community structure and soil total C were highly significant (p = 0.007). Correlation between AOA structure and soil total N was also significant (p = 0.014). AOB structure did not correlate to any of the measured relevant environmental variables. The ratio between AOA and AOB abundance, assessed by quantitative real time PCR, displayed a linear correlation with carbon to nitrogen (C/N) ratio. The nitrification potential, a proxy for ammonia oxidizing activity, correlated to total nitrogen and with the abundance of ammonia oxidizing bacteria, but not with abundance of ammonia oxidizing archaea. In conclusion, in no-till systems the abundance and compositionof AOA communities exhibit a biogeographical pattern, whereas AOB appears to be shaped largely by environmental factors.