Response of the Soil Microbial Community to Fertilization Practices in Agricultural and Native Cerrado Systems in Brazil
Marirosa
Molina, U.S EPA, molina.marirosa@epa.gov
(Presenting)
Laura
Tillman
Viana, University of Brasilia, lviana@unb.br
Mercedes
Maria Cunha
Bustamante, University of Brasilia, mercedes@unb.br
Richard
G.
Zepp, U.S. EPA, zepp.richard@epa.gov
Agricultural practices in the Cerrado (tropical savannah) and Amazon regions in Brazil have increased drastically during the last decade causing dramatic changes in the nutrient and carbon cycling of native areas, and producing changes on the microbial community structure. We compared microbial communities under a range of management practices which included different native areas (savannah and forest), an agricultural site, and a Cerrado area subjected to fertilization treatments (N, P, N+P, Ca) using phospholipid fatty acid analysis (PLFAs) and fungal to bacterial ratios. In the native Cerrado, samples were collected 10, 20 and 40 days after fertilizer application from four plots (15 x15m) per treatment in a completely randomized design. Although the total PLFA concentration did not show significant differences among the sites, principal component analysis indicated that the structure of the microbial community varied as a function of the fertilization treatment and management practice (p<0.0001). In the fertilization experiment, N, P, and N+P treatments had a higher concentration of Gram positive biomarkers than the control and exhibited similar microbial communities. P amendments produced a higher fungal:bacterial ratio after 10 days of fertilization and was the only treatment showing a significant difference in the ratios. Fungal:bacterial ratios were also significantly higher in the pasture site when compared to the ratios observed in the native savannah and Amazon soils. The higher ratio in the pasture site correlated with lower availability of nitrogen and was a function of a decrease in the % composition of bacterial PLFAs. The results suggest a phosphorus limitation on the fungal community inhabiting native Cerrado soils, while in pastures, nitrogen seems to limit the bacterial community, but has no effect on the fungi.