Interactions between soil characteristics and soil microbiota influence soil ecosystem processes such as nitrification however, their complexity makes interpretation difficult. Furthermore, the impact of soil management systems on abundance and activity of soil microbial community is poorly understood, especially in the Neotropics. To investigate these interactions, the effects of tillage, inorganic fertilization, and plant cover on the abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were assessed by quantification of the marker gene (amoA) during different stages of soybean cultivation in a site under restoration from gravel extraction in the Central Brazilian Savanna (Cerrado). Results of molecular analysis and classic and isotope techniques showed that levels of organic C and NH4 +–N were higher in the soybean field during fallow than in an adjacent undisturbed field (Campo sujo). Ammonia oxidizer abundance and nitrification rates were also higher in the agricultural soil than in the undisturbed site, with the lowest ammonium/nitrate ratio in tilled soil. Soil δ15N was lower in the undisturbed soil than the agricultural soil. Both AOA and AOB were more abundant during soybean crop transitional stages, and this increase positively correlated with soil pH, particularly for AOB abundance, in tilled soil and within the soybean rhizosphere. The results suggest that AOB have more copiotrophic characteristics than AOA and are better able to change available ammonium in the soil. The combination of standard soil ecological methods and modern molecular analysis show the short-term modification of ammonia oxidizer abundance and soil N dynamics in a managed system within the Cerrado biome.
Bibliographical noteAcknowledgments: The authors are very grateful to Mr. Fabiano Bielefeld Nardotto, owner of the Tabapuã dos Pireneus farm, for allowing our free movement around the farm and collection of soil samples, as well as providing information about soybean cultivation. The authors also thank Dr. Plínio de Camargo, who performed the isotopic analysis in the CENA laboratory at the University of São Paulo (USP). This work was supported by grants from the National Council of Technological and Scientific Development (CNPq), Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES), and Foundation for Research Support of Distrito Federal (FAP-DF).
- Ammonia oxidizers
- Central Brazilian Savanna