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An exploration into the chemicalmakeup of soil and its influence
on microbial soil profiles. Howdoes this affect the validity of
using decomposition microbes
found in soil, as forensic tools?
Catherine L. Aindow : 200805506 Project Supervisor: Dr L.
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Aims of this presentation
Pesticide application
Carbon: Nitrogen cycle
Vegetation type and density
Effects upon microbial soil populations
Can microbial soil profiles be linked tosites of cadaver decomposition?
Could these variables renderhypothesis untrue?
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Soil Composition andVariables Soil is a complex matrix of inorganic
and organic compounds.
Supports the growth of a variety of
microorganisms. Variables that affect chemical and
microbial composition within soil.
Influences the carbon to nitrogen bio-cycle within soil.
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Carbon : Nitrogen CycleClimate
Temperature, SoilFertility, WaterContent. Etc.
Plant growth
Labile litter androot fluids low
C:N ratio
Recalcitrant litterhigh C:N ratio
Carbonallocation to
plant roots
Bacteria(sacrophytic)
Fungi(sacrophytic)
EM,ECMfungi
(symbiotic)
AM fungi
(symbiotic)
Bacteria
(symbiotic)
N, P (mineral)
N, P (organic)
N (air)
high low
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Cadaver Decomposition
Cadaverdecomposition altersnatural bio-cycle within
soil. Release of lipids,
proteins and aminoacids into soil.
Influences the growthof specific microbes.
Microbial profiling may
distinguish sites of
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Effects of Pesticide Applicationupon Soil Communities
Study conducted to showthe effects of commonpesticide Carbendazim
upon chemical makeup ofsoil.
A range of organisms were
examined includingnematode populations.
Employed use of
microcosmic conditions.
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Methodology (Microcosm)
Addition of artificalrainwater 12 hour light-dark
cycle maintined.
6 samples (30 kgeach)
Polyethylene pipes Nylon mesh for
leachate collection. Addition of 3
earthworms persample
Sown with approx.
10 wheat seeds Soil-pesticide
mixtures thoroughlymixed beforepacked.
Did not account for daylightsaving
Method does not correctlyimitate the way in whichpesticide would settle upon
the soil.
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Methodology (The Process)
Dose sampleslabelled T0 up to T5
T0 Ionized water
T10.76
T22.28
T3 6.84
T4 20.52
T5 61.56 (concs: a.i. kg-1 soil
dry mass)
400 ml sprayed
Nitrogen andammonium concsmeasured beforetreatment and after7,14,28 and 56 days.
Extraction
Colorimetric methodused for quantification(650 nm).
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Nitrate Concentrations afterTreatment
Dose levels T4 & T5 increase nitrate
concentrations significantly in comparison toother dose levels.
Soil chemistry able to recover after 56 days.
Recovery may be due to shoot growth.
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Vegetationgrowth and
NitrateConcentrations
Shoot growth (grams) after treatment with knownconcentrations of Carbendazim
Nitrate concentration after treatment with knownconcentrations of Carbendazim
Shoot growth increasesdramatically after 56days of treatment with
all concentrations ofCarbendazim. Increase in shoot
growth is also seen incontrol.
Therefore pesticide
application does notseem to hindervegetation growth.
Correlation betweenvegetation growth andnitrate concentrations.
State of homeostasisachieved.
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Conclusion from experiment
Pesticide application does alter chemical
makeup of soil. Increases nitrate concentrations. Potentially would influence microbial
populations that thrive in low C:N
environments. Would render influence of cadaver
decomposition upon soil profilesirrelevant.
Vegetation growth may combat adverseeffects.
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The effects of vegetation type anddensity upon microbial soil
populations Study took place within a forest in Sweden
(Betsele).
3 transects of land: 90m long & between 25m and
70m apart. Dwarf shrub (DS), short herb (SH) and tall herb
(TH) vegetation types were analysed.
DS
E.g. species: Vacciniummyrtillus
Open and of low productivity.
SH
E.g. species: Oxalicacetosella
Characterized by severalshort herbs
TH
E.g. species: Actae spicata
Dominated by pineas abies
forest & has high soil pH andnitrogen.
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Methodology
Aimed to identifychemical andmicrobiologicaldifferences betweenbiomes.
Soil samples taken in
triplicate on 18th
August2004
Samples were taken viaa 0.15m auger and thenincorporated into onebulk sample for eachtransect.
Samples were siftedthrough sieve
Chemical analysis
PLFA analysis
Sample storage
NOTE After sifting samples were weighed out into
appropriate amounts no value was stated. Extraction method Bligh & Dyer method PLFA analysis silica gel columns, then eluted
in sequence with chloroform acetone andmethanol.
Specific method of chemical testing was also
not stated.
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Results(Chemistry)
Soil chemistry observed in Betsele sites
Site ForestType
Treat-ment
pH C to NRatio
NH4-N(g g-1
o.m.)
NO3-N(g g-1
o.m.)
Betsele
DS - 4.0 38.1 4.6 0.9
SH - 4.6 22.9 5.2 0.7
TH - 5.3 14.9 15.9 3.4
P-value
- -
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PLFA Analysis No significant
difference withintotal PLFA massbetween biomes
Fungal bacteriamass decreased asvegetation thickened
Total amount ofbacteria increasesas vegetationthickened.
Due to an increasein gram negativebacterial levels.
Gram positivebacterial levels did
not alter significantly. Fungi to bacteria
ratio decreased asvegetationthickened.
Distinctive microbialprofiling betweendifferent biomes.
Combination of highpH and highnitrogen levelsfavours the growthof gram negativebacteria.
Deters growth offungi.
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Effects of nitrogen loading uponcarbon: nitrogen ratio Site in Sweden (Norrliden)
All sites DS
Total of 15 plots investigated(4 concs - 3 replicates foreach).
4 concentrations of nitrogen(in form of NH4NO4)
1 control (given aconcentration of 3kg N ha-1year-1)
N3 was discontinued at anearlier date to see how soilchemistry would recoverfrom loading
N0 control
N1 34 kg N ha-1 year-1 N2 68 kg N ha-1 year-1
N3 108 kg N ha-1 year-1
N1 & N2 treated from 1971-2004
N2 treated from 1971 1990 Samples were taken on 25th
August 2004
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NORRLIDEN RESULTS(CHEMISTRY)Site Forest
TypeTreatment pH C to N
ratioNH4-N(g g-1o.m.)
NO3-N(g g-1o.m.)
Norrliden
DS N0 4.1 37.5 0.5 0.7
DS N1 4.1 31.1 39.9 1.5
DS N2 4.2 27.7 88.4 7.3
DS N3 4.1 27.2 3.3 0.6
P-Value - -
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Nitrogen loadingPLFA results
(Norrliden site) Total PLFA contentdecreases with highlevels of nitrogenloading.
Fungal biomass also
decreases with theaddition of nitrogenhowever appears torecover aftertreatmentdiscontinuation.
No significant changeis seen within thebacterial populations,though there is aslight increase in
gram positivebiomarkers asnitrogen levelsincrease.
Fungi to bacteria
ratio decreases asfungi biomarkerlevels drop and grampositive bacteriabiomarkers increase(slightly).
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Discussion
Many similarities betweenmicrobial communities that havesame biome.
Gram positive markers able towithstand nitrogen loading and
therefore would withstandchanges made by pesticides.
Gram positive bacteriabiomarker levels did not differacross different biomes
Further study conductedshowed no change in gram
positive PLFA biomarkersacross a tree-girdlingexperiment. (Not affected bywater content).
Since gram positive bacteriado not change across biomes
and across different chemicalmakeups, could be a goodcandidate for a decompositionbiomarker.
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How would it work?
Decomposition ofcadaver wouldrelease intestinal
bacteria. Would also alter
chemical makeupof soil.
Which wouldinfluence changeswithin soil profiles
Increase in grampositive bacteriawithin soil samples
could only then beattributed tocadaverassociation
May also indicatewhere body hasbeen moved from.
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Problems
No concreteground for provingthis hypothesis.
More work wouldneed to be carriedout.
Too many
variables andinfluences.
No soil profile is
the same.
Just too much toconsider to rely on
decompositionmicrobes as aforensic tools.
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Any Questions?