Transcript 39.18-P.ppt

Effects of land use on soil microbial communities in
the Cerrado region
1Silva,
M. R. S. S., 1Bresolin, J. D., 2Krüger, R. H., 1Bustamante, M. M. C., 3 Reis Jr., F. B.
1 Departamento de Ecologia, Universidade de Brasília, Brasília, DF.
2 Universidade Católica de Brasília, DF.
3 EMBRAPA – Cerrados, Planaltina, DF.
The differences between burned and unburned plots were detected after the first rain events.
Introduction
FP (set/02)
The composition and activity of soil microbial communities largely determine
biogeochemical cycles, the turnover process of organic matter, and the fertility and
quality of soils. The intensification of agricultural activities in the Cerrado region
results in the replacement of native vegetation cover, changes in fire regime and
soil physical and chemical properties. Biomass burning can affect biogeochemical
cycles through direct transformation of the elements during combustion process
and through environmental changes that could affect the nutrient dynamics for
many years after fire. Our objective was to analyze the diversity of the soil
bacterial communities from native Cerrado areas (burned and unburned) and from
pasture areas using a molecular technique (PCR-DGGE).
UCS (out/02)
BC 10d (out/02)
BCS 30d (out/02)
UC (out/02)
BC (out/02)
UCS (set/02)
BC 2d (out/02)
BCS 10d (out/02)
Fig.1. Dendogram of PCR-DGGE analysis of the bacteria communities in Cerrado soils from
unburned and burned native areas (campo sujo and cerrado restricted sense) and pasture.
Samples FP represent fertilized pasture, UCS – unburned campo sujo, UB – burned campo
sujo, BC – burned cerrado, UC – unburned cerrado.
Material and Methods
The comparison between DGGE profiles from unburned native areas,
campo sujo and cerrado restricted sense, showed differences for
seasonality and vegetation types.
Soil sampling
FP (set/02)
UCS (out/02)
The soils are classified as Oxisols, very acidic, with high aluminum saturation and
low cation exchange capacity. Soils samples were taken from the Ecological
Reserve of the IBGE, Brasilia, Brazil and from Rio de Janeiro farm, Planaltina,
Brazil. Soils were taken from 0-5 cm depth in native Cerrado areas (campo sujo
and cerrado restricted sense) and in pasture areas {fertilizated pasture,
unfertilizated pasture, young pasture, mixed pasture (grass/legume)} . The
burned and unburned plots of the two native vegetation types were sampled 2, 10
and 30 days after burning. The samples were collected during the wet and dry
season as well as during the transition wet to dry season.
UCS (dez/02)
UC (out/02)
UC (dez/02)
UCS (set/02)
UCS (jul/02)
DNA extraction
PF (set/02)
CSNQ (out/02)
Soil DNA was obtained by direct extraction with a protocol which included
mechanical lyses of cells, phenol and chloroform extractions, a potassium
acetate precipitation and a final purification using the Wizard DNA clean up Kit.
Fig.2. Dendogram of PCR-DGGE analysis of the bacterial communities in Cerrado soils from
unburned native area (campo sujo and cerrado restricted sense) and pasture. Samples FP
represent fertilized pasture, UCS – unburned campo sujo, UC – unburned cerrado.
Pasture with grass/legume showed a DDGE profile similar from burned campo sujo native area.
PCR
The 16S rDNA primers used in PCR were 968F and 1401R, which are commonly
used to analyze bacterial communities.
FP (set/02)
YP (set/02)
DGGE
DGGE was carried out using a Bio-Rad Dcode Universal Mutation Detection
System at 70V and 60° C for 18 h in 0.5x TAE buffer. The 6% (w/v)
polyacrilamide gels were made with a denaturing gradient ranging from 40 to
70% and used with PCR products. After electrophoresis, gels were stained for 40
minutes with SYBR green I and photographed on a UV transilumination table
with a Kodak digital camera.
DGGE analysis
Gel pictures were manually converted to 1/10 matrices, which were used for
clustering by the unweighted pair group method with mathematical averages
(UPGMA; Dice coefficient of similarity), followed by tree inference.
MP (set/02)
BCS (dez/02)
UP (set/02)
BCS (abr/03)
BCS 10d (out/02)
Fig.3. Dendogram of PCR-DGGE analysis of the bacterial communities in Cerrado soils from
burned native area (campo sujo) and pasture. Samples FP represent fertilized pasture, YP –
young pasture, MP – mixed pasture (grass/legume), UP – unfertilized pasture, BCS –
burned campo sujo.
Results
A comparison of the DGGE profiles from soil from burned and unburned native
areas, showed no differences in the bacterial community between the areas
after the prescribed fire. The differences between burned and unburned plots
were detected after the first rain events (Fig.1). The comparison between DGGE
profiles from unburned native areas, campo sujo and cerrado restricted sense,
showed differences for seasonality and vegetation types (Fig. 2).
Analysis from DDGE profiles from soil from pasture showed differences between
treatments for pasture restoration. Pasture with grass/legume showed a DDGE
profile similar from burned campo sujo native area (Fig. 3).
Conclusions
The first rain effects were more important to determine differences in
the bacterial communities from native areas than burning.
In the wet season, bacterial communities profiles from unburned native
areas showed differences between vegetation types.
In the pasture areas, time of conversion (native areas to pasture), input
of P and consortium grass/legume were relevant to diferentiate
bacterial communities.